Bone mineral density in archaeological populations of Norway: Temporal patterns of bone loss related to age, sex, and socioeconomic status in the 8th - 19th centuries AD

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Bone mineral density in archaeological populations of Norway

Temporal patterns of bone loss related to age, sex, and socioeconomic status in the 8th - 19th centuries AD

Doctoral thesis Elin T. Brødholt by

Division of Anatomy

Institute of Basic Medical Sciences Faculty of Medicine

UNIVERSITY OF OSLO

2023

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© Elin T. Brødholt, 2023

Series of dissertations submitted to the Faculty of Medicine, University of Oslo

ISBN 978-82-348-0174-7

reproduced or transmitted, in any form or by any means, without permission.

Cover: UiO.

Print production: Graphics Center, University of Oslo.

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Special thanks go to my supervisor and co-author, Per Holck, at the Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, who took me in as a visiting master’s student in 2004, introduced me to the Schreiner Collection, taught me all about pathology, and encouraged me to use my skills as a forensic anthropologist.

I would also like to acknowledge the contribution of my supervisor and co-author, Torstein Sjøvold, Stockholm University, for all support and encouragement from the time of my master thesis at Gotland University College/Stockholm University onwards.

I thank my principal supervisor Trygve Brauns Leergaard for keeping an overview of the thesis work, article revisions, and practical advice. I am grateful to my other co-authors, Kaare M.

Gautvik, the Unger-Vetlesen Institute, Lovisenberg Diaconal Hospital, for support, discussion, and paper improvements. Clara-Cecilie Günther at the Norwegian Computing Center for statistical analysis, advice, and discussions. For valuable contributions and support, Ole Jørgen Benedictow, the Department of Archaeology, Conservation and History, University of Oslo.

I thank Haakon Breien Benestad at the Section of Anatomy, Institute of Basic Medical Sciences, University of Oslo, for undertaking the midterm review.

I want to acknowledge the contribution of all reviewers; Kari Ormstad, Department of Forensic Sciences, Oslo University Hospital, and Inger Karlberg at the Department of Archaeology,

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- 2 - Viken County Municipality. Thank you for thoroughly evaluating the manuscript and your insightful comments and positivity.

Special thanks go to my colleagues at the Institute of Basic Medical Sciences, specifically at the Photo and Graphics Services and the Mechanical Workshop, for including me and sharing numerous cups of coffee and cake. These years of thesis work would not have been the same without all members of our wine tasting and tapas club. Thank you for many great experiences, conversations, and happy moments. I sincerely thank the office Canary, for always being there, for all support and mischief. You are the best!

I am grateful for my colleagues at my second job, the Department of Forensic Sciences, Oslo University Hospital. Thank you for your open arms, challenges, interest, and support.

Finally, I am grateful to my family, the only ones that matter.

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PAPERS

Paper I

Brødholt, E. T., Günther, C.-C., Gautvik, K. M., Sjøvold, T., & Holck, P. (2021). Bone mineral density through history: Dual-energy X-ray absorptiometry in archaeological populations of Norway. Journal of Archaeological Science: Reports, 36, 102792.

https://doi.org/:10.1016/j.jasrep.2021.102792

Paper II

Brødholt, E. T., Gautvik, K., Günther, C.-C., Holck, P., & Sjøvold, T. Social stratification reflected in bone mineral density and stature: Spectral imaging and osteoarchaeological findings from medieval Norway (under review).

Paper III

Brødholt, E. T., Gautvik, K., Benedictow, O. J., Günther, C.-C., Sjøvold, T., & Holck, P.

Female skeletal health and socioeconomic status in Medieval Norway (11th-16th centuries AD): analysis of bone mineral density and stature (under review).

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SYNOPSIS

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INTRODUCTION AND BACKGROUND

BRIEF HISTORY OF RESEARCH Contemporary relevance

Osteoporosis is a significant health concern in modern society, leading to fragility fractures and representing a major population health problem with substantial social and economic challenges (Hernlund et al., 2013). The current clinical and epidemiological knowledge of osteoporosis has been acquired during the past 70 years (Curate, 2014). Osteoporosis was for a long time believed to be a modern disease; however, paleopathological examinations of archaeological remains have demonstrated its existence throughout human history (Agarwal, 2008; Agarwal, 2021; Agarwal & Grynpas, 1996; Curate, 2014; Turner-Walker, Syversen, &

Mays, 2017).

The insights produced by these paleopathological studies have strengthened the modern clinical understanding of bone loss leading to osteoporosis. They offer a window into the natural history of bone loss and aging in populations from biological, social, and cultural contexts that differ significantly from most contemporary societies (Agarwal, 2021). These investigations have demonstrated that the patterns of bone loss are not uniform and provided insight into the diachronic evolution of this condition (Curate, 2014).

Bone loss in archaeological populations

Examinations of bone mineral density (BMD) in past populations have provided valuable information to improve our understanding of living conditions and quality of life in past populations and complement other archaeological sources (Turner-Walker et al., 2017). Many methods have been used to investigate bone loss in archaeological skeletal material; however, Dual-Energy X-Ray Absorptiometry (DXA) is considered the gold standard when assessing BMD in a clinical setting (Brickley, Ives, & Mays, 2020). The earliest paleopathological studies of bone loss in past populations carried out in the 1970-80s documented a homogenous pattern of sex and age-related bone loss, characterized by greater bone loss in females (Curate

& Tavares, 2018). Later research on European skeletal material, mainly from contexts considerably different from most modern societies, uncovered various degrees of bone loss in past populations, but the findings have been inconsistent (Agarwal, 2021; Agarwal & Grynpas, 1996; Mays, 1999). Some studies detected less bone loss in past populations than in modern populations (Drusini, Bredariol, Carrara, & Rippa Bonati, 2000; Lees, Molleson, Arnett, &

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- 6 - Stevenson, 1993; Mays, 2000; Rewekant, 2001) or insignificant to no bone mass reduction with age in one or both sexes (Agarwal, Dumitriu, Tomlinson, & Grynpas, 2004; Brickley &

Howell, 1999; Ekenman, Eriksson, & Lindgren, 1995; Poulsen, Qvesel, Brixen, Vesterby, &

Boldsen, 2001). Several studies have shown early (premenopausal) bone loss in females (Holck, 2007; Mays, Turner-Walker, & Syversen, 2006; Mays, 2006; Poulsen et al., 2001;

Rewekant, 2001; Turner-Walker et al., 2017). Other examinations revealed a notable postmenopausal bone loss similar to the pattern observed in modern populations (Curate, Lopes, & Cunha, 2010; Glencross & Agarwal, 2011; Hammerl, Protsch, Happ, Frohn, & Hör, 1991; Kneissel et al., 1994; Mafart, Fulpin, & Chouc, 2008; Mays, Lees, & Stevenson, 1998;

Mays, 1996; McEwan, Mays, & Blake, 2004; Zaki, Hussien, & El Banna, 2009).

Research on bone mass variation in archaeological skeletal material from Norway has mainly focused on the medieval period (Mays et al., 2006; Turner-Walker, Syversen, & Mays, 2000; Turner-Walker et al., 2017), with few conclusive results regarding long-term trends and patterns of BMD changes comparing prehistoric and modern populations. In Norway, Holck (2007) examined temporal BMD variation in prehistoric, Viking Age, and medieval femur samples using DXA-analysis and found no significant differences in femur neck mean BMD between these periods (p = 0.151). The results were interpreted to indicate that the study cohorts experienced similar physical strains and skeletal loading in these periods. Furthermore, the study did not detect a significant difference in mean BMD between the sexes (p = 0.554, p = 0.353 and 0.371). Females experienced a rapid decrease in BMD until the age of 40, followed by an immediate increase, while males experienced a slower, more gradual bone loss. The medieval bones showed a significantly higher mean BMD than the modern reference population (p = 0.001). The skeletal remains from the medieval period were separated into urban, rural, and monastic populations, and the analysis detected a significant difference in average BMD between the monastic and the rural population. The monastic group (Dominican friars) had higher BMD values than the rural peasants, and this result was discussed in relation to the assumed level of physical activity in these groups.

Turner-Walker, Syversen, et al. (2000); (2017) compared the age-related bone loss in two medieval populations, one from Trondheim, Norway, and the second from Wharram Percy, England, using DXA-analysis of the femur bone. They found no significant differences and concluded that modern-day differences in the occurrence of osteoporosis and fracture incidence between these two countries might not reflect genetic differences but environmental factors.

Moreover, they reported a significant early bone loss in reproductive females, followed by an

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- 7 - increase in BMD after the age of 35, leading to a postmenopausal bone loss characteristic for modern females.

Mays et al. (2006) examined skeletal material from medieval Trondheim (femur, DXA) and compared the results to previously reported results from Wharram Percy, England, demonstrated that peak BMD and age-related loss of BMD were similar in these groups.

Accordingly, the authors concluded that the current differences in BMD between the Norwegian and British populations are of recent origin. For the females, they hypothesized that age-related bone loss in women started earlier than today. This early (pre- or perimenopausal) bone loss was seen in connection with a different practice regarding childbearing: early onset, high parity, and late weaning compared to modern populations. The males from medieval Trondheim displayed a significant difference in BMD between young adults (18-29 years) and the other two age groups (30-49 and 50+ years). However, the lack of significant late bone loss, similar to the age-related bone loss experienced in modern males, could be due to small sample sizes.

The factors involved in bone loss in past populations are multiple, complex, and often symbiotic, sensu Weaver (1998). Therefore, it is difficult to fill the gaps between the past and the present (Curate & Tavares, 2018). To address the observed patterns in any given past population, a multidisciplinary, in-depth mapping of cumulative factors possibly influencing BMD over the life course, positively or negatively, is imperative and requires contextualization at the individual and population level (Agarwal, 2021). The existing findings regarding temporal trends and BMD changes in past populations in Scandinavia and Norway, in particular, are few, inconsistent, and inconclusive. The present study attempts to fill this knowledge gap and discuss previous and current research.

BONE MINERAL DENSITY General overview

BMD is a measure of the inorganic component of bone tissue (mainly hydroxyapatite) and is often assessed by DXA in a clinical setting (Curate & Tavares, 2018; Litak et al., 2022). Adult individuals experience a daily removal of small amounts of bone mineral (resorption), balanced by an equal deposition of new mineral (formation). The continuous process of replacing old bone tissue is called remodeling and is designed to maintain bone structure and strength.

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- 8 - However, when this balance is disturbed by excessive resorption, the structure deteriorates bones over time and becomes fragile and osteoporotic. The risk of developing osteoporosis is greatly affected by non-modifiable and modifiable factors (IOF, 2021).

Non-modifiable risk factors

Non-modifiable (fixed) risk factors cannot be controlled or changed, but preventive strategies can lessen their effect. Non-modifiable risk factors include female gender (females are more susceptible to bone loss), age (50 years or older), heredity (osteoporosis has a significant genetic component), ethnicity (Caucasian and Asian populations are affected to a larger degree), menopause (loss of estrogen) (IOF, 2021; Pouresmaeili, Kamalidehghan, Kamarehei,

& Goh, 2018) and height (tall people have a higher risk) (Meyer, 2016).

Modifiable risk factors

Modifiable risk factors are related to personal lifestyle choices and can be avoided or ameliorated. Most of them directly impact bone and result in decreased BMD, which may increase the risk of fracture. These risk factors include physical inactivity (a sedentary lifestyle), smoking (reduced bone density and increased risk of fracture), alcohol (high intake causes secondary osteoporosis), poor diet (low dietary calcium intake), and vitamin D deficiency (insufficient sun exposure) (IOF, 2021; Pouresmaeili et al., 2018). Lifestyle choices influence 20-40 % of the maximum attained bone mass in adulthood (Weaver et al., 2016).

SEX- AND AGE-RELATED BONE MASS VARIATION Childhood and Puberty

The amount of bone mass acquired from birth to adulthood follows distinct age- and sex- specific patterns (Heaney et al., 2000). The most rapid skeletal growth occurs within two years after birth, and a second skeletal growth burst corresponds to prepuberty. The increase in bone mass during puberty is greater in boys than in girls due to a more prolonged period of accelerated growth (Bonjour, 2001; Bonjour, Theintz, Law, Slosman, & Rizzoli, 1994, 1995).

Before puberty, boys and girls acquire bone mass at similar rates. After puberty, however, men

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- 9 - tend to acquire a greater bone mass than women (NIH, 2015), apparently due to a prolonged bone maturation period (Bonjour et al., 1994).

Peak bone mass

Peak bone mass (PBM) refers to the maximum amount of bone an individual has accrued during young adulthood (Weaver et al., 2016), precisely a few years after the fusion of the long bone epiphyses (Heaney et al., 2000). PBM is usually higher in men than women; however, both sexes acquire bone mass at similar rates up until puberty (NIH, 2015). The development of an individual's PBM is under substantial genetic control (60–80 %) (Nguyen, Howard, Kelly,

& Eisman, 1998; Weaver et al., 2016) and show ethnic differences. PBM is modified by pre- and post-natal determinants, e.g., nutrition, vitamin supply, and presence of chronic diseases.

Kersh, Martelli, Zebaze, Seeman, and Pandy (2018) state that physical activity is perhaps the single most important lifestyle factor influencing PBM. The benefits of physical activity/weight-bearing exercise and mechanical loading on bone mass during the growing years are widely documented. Failure to obtain the genetically determined maximum (peak) bone mass during development and maturation is strongly associated with the risk of developing osteoporosis (Heaney et al., 2000; Hernandez, Beaupre, & Carter, 2003).

Adulthood

Actual adult bone mass equals the PBM attained during young adulthood minus the amount of bone loss occurring afterward (Rizzoli, Bonjour, & Ferrari, 2001). The reduction of bone mass is a natural part of the aging process in both sexes but is especially marked in women after menopause (Agarwal & Stout, 2003; Aufderheide & Rodríguez-Martín, 1998). Natural bone mass reduction occurs gradually after age 30 (Karaguzel & Holick, 2010). Modern women tend to experience little change in total bone mass between age 30 and the onset of menopause (in their late 40s or early 50s), followed by a more rapid bone loss. This rapid bone loss slows down 8-10 years after menopause (NIH, 2015). Men, however, experience a more gradual bone loss throughout their adult life, from age 40 onwards (Clarke & Khosla, 2010). Suboptimal lifestyle factors, especially between the ages of 10 to 18, may result in reduced bone mass and strength in adulthood (Bonjour, 2001; Khosla & Riggs, 2005; Weaver et al., 2016). While PBM is predominantly genetically determined, our age-dependent bone mass is influenced by various variables such as sex, nutrition, endocrine factors, mechanical strain, disease, and

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- 10 - exposure to risk factors (Bonjour et al., 1994; Khosla & Riggs, 2005). Age-related bone loss also occurs secondary to most chronic diseases, excessive alcohol intake, smoking, and reduced physical activity (Falch, Kaastad, Bohler, Espeland, & Sundsvold, 1993; Hollenbach, Barrett- Connor, Edelstein, & Holbrook, 1993; Naessen, Parker, Persson, Zack, & Adami, 1989;

Paganini-Hill, Chao, Ross, & Henderson, 1991; Turner-Walker et al., 2017). Lack of weight- bearing exercise, sunlight exposure (Healthline, 2021), vitamin D deficiency, and steroid use (Holck, 2007; Meyer, Falch, O'Neill, Tverdal, & Varlow, 1995) are other factors of influence.

As noted by Agarwal (2012), our skeletons are influenced by multiple biocultural influences throughout life, and preceding life events can alter the trajectory of bone development later in life.

OSTEOPENIA AND OSTEOPOROSIS General overview

Osteopenia denotes lower than normal bone density and is usually a precursor to osteoporosis.

The diagnostic difference between osteopenia and osteoporosis is based on the measure of BMD by DXA, as defined by the World Health Organization (WHO) (Kanis, Melton, Christiansen, Johnston, & Khaltaev, 1994; Karaguzel & Holick, 2010). Osteoporosis (meaning

“porous bone”) is a progressive and silent disease, usually not discovered until the incidence of a fragility fracture (NIH, 2019). It is characterized by bone tissue microarchitectural deterioration and bone mass loss (Clynes et al., 2020). Women are more susceptible to osteoporosis than men due to their lower attainment of PBM and the amplified bone loss following menopause (NIH, 2015, 2019). While bone loss is an age-related and postmenopausal phenomenon, the risk of developing osteoporosis is greatly affected by independent factors, such as physical activity, parity, and lactation (Agarwal & Glencross, 2010) and also shows genetic variability (Cauley, 2011; Pothiwala, Evans, & Chapman- Novakofski, 2006). Osteoporosis and age-related fractures are closely associated, and research has shown that low BMD heightens the risk of almost all types of fractures (Cooper et al., 2011). Fracture rates exhibit a positive correlation with socioeconomic status (SES), level of education, and health (Cauley, Chalhoub, Kassem, & Fuleihan Gel, 2014) and are seemingly associated with a Western lifestyle (Rosengren, Bjork, Cooper, & Abrahamsen, 2017).

The time until BMD falls under the threshold for osteoporosis is, to a large degree, dependent upon the maximum (peak) attained bone mass (Bonjour et al., 1994, 1995; Heaney

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- 11 - et al., 2000), more so than the rate of age-related (non-menopausal) bone loss or time of menopause (Hernandez et al., 2003).

Prevalence in modern populations

In the European Union, 22 million women and 5.5 million men are estimated to have osteoporosis. The economic burden of fragility fractures related to osteoporosis is substantial (€ 37 billion) and is expected to increase due to aging populations (Hernlund et al., 2013). The population in most countries and areas is growing older due to increased longevity combined with lower fertility (UN, 2019). It is estimated that 240 000 – 300 000 Norwegians have osteoporosis, and ca. 9000 individuals fracture their hip each year (Meyer, 2016). In Scandinavia, the number of hip fractures in women is among the highest in the world, although the cause of this high fracture incidence is largely unknown. One possible explanation for the high incidence of hip fractures in Norwegian women could be that they are generally taller and have lower body weight; however, this is by far the only reason (Meyer, 2016; Meyer et al., 1995). Research on hip fractures in Norway and Sweden has demonstrated a secular increase in fracture rates in both sexes since the 1960s (Falch et al., 1993; Naessen et al., 1989). In Norway, the hip fracture risk has declined since the millennium, although the total annual number of fractures has remained stable due to the growing number of elderly (Meyer, 2016).

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THESIS AIMS AND RESEARCH QUESTIONS

Information regarding temporal variation in BMD related to age, sex, and SES in archaeological populations in Norway is insufficient and partly contradictory (see page 9). This study addresses this subject by aiming to bridge the present knowledge gap and expand the current field of knowledge. The study spans the 8th – 19th centuries AD in Norway and combines osteology and DXA-analysis to present the most extensive skeletal material examined so far. Finally, the results are discussed in relation to modifiable and non-modifiable factors.

AIMS

1. To study the long-term historical pattern of BMD variation in archaeological populations of Norway, spanning from the 8^th to 19^th century.

2. To explore possible associations between BMD and SES in medieval Norway.

3. To examine bone loss in female skeletal remains from medieval Norway in relation to information about SES.

RESEARCH QUESTIONS

Paper I What are the long-term trends and patterns of age- and sex-related variation in BMD in archaeological populations of Norway?

How does the age- and sex-related variation in BMD and patterns of bone loss compare to the pattern observed in modern populations?

Paper II Can distinct SES be reflected in BMD variation and patterns of bone loss in medieval Norwegian skeletal remains (11^th – 16^th centuries AD)?

Paper III Can female skeletal health and SES be associated with bone loss and stature patterns in medieval Norway (11^th – 16^th centuries AD)?

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MATERIALS AND METHODS

The skeletal material included in this study consists of inhumation burials and is part of the Schreiner Collection at the Division of Anatomy, University of Oslo. We examined femur bones from 222 adult individuals from Eastern Norway, spanning the 11-19^th Century, with DXA (Fig. 1, Table 1). In addition, data from a previous DXA study (Holck, 2007) of 137 individuals dating to the Late Iron Age and medieval period in Norway were included in the study. All skeletal material included in the study underwent osteological analysis before DXA scanning to evaluate sex, age, stature, pathology, and injuries pertaining to each skeleton, in addition to state of preservation and completeness. Overall, 1256 skeletal finds (anthropological numbers) from the medieval period and 188 from the post-Reformation period were examined osteologically and assessed according to the DXA-analysis inclusion criteria.

Damaged or incomplete femora and bones exhibiting pathologies known to influence BMD were excluded from the DXA analysis. The principal material was femur bones, and the femur neck (collum femoris) was defined as the region of interest (Fig. 2). Comprehensive technical details concerning the DXA analysis, inclusion criteria, soft tissue substitute, standardization, validation of precision, and cross-calibration are described in detail in paper

Fig. 1. Burial sites in Eastern Norway included in the study. Adapted from Brødholt, Gautvik et al. (2021).

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- 14 - Time Period Burial site, County SES n Sex Age Total

YA MA OA

Medieval Church of St. Mary, Oslo High F 8 8 3 19

(1030-1536 AD) M 16 20 14 50

Total 69

Hamar Cathedral, Innlandet Parish F 9 16 29 54

M 25 15 13 53

Total 107

Total MP F 17 24 32 73

M 41 35 27 103

Total 176

Post-Reformation Christiania Tukthus, Oslo Low F 11 1 0 12

(1537-1880 AD) M 7 8 1 16

Total 28

Tangen Church, Viken High F 2 4 2 8

M 3 4 3 10

Total 18

Total PRP F 13 5 2 20

M 10 12 4 26

Total 46

Total F 30 29 34 93

M 51 47 31 129

Total 222

HOLCK (2007)

Late Iron Age Scattered burials High F 11 4 2 17

(750-1030 AD) M 7 12 12 31

Total LIA 48

Medieval Period Church of St. Mary, Oslo¹ High F 2 5 1 8

(1030-1536 AD) M 5 2 3 10

Total 18

St. Clemens Church, Oslo Parish F 4 2 4 10

M 5 2 2 9

Total 19

St. Olav's Monastery, Oslo Mixed F 5 2 2 9

M 5 4 3 12

Total 21

Prestgardskirken, Innlandet Parish F 2 5 8 15

M 2 4 10 16

Total 31

Total MP F 13 14 15 42

M 17 12 18 47

Total 89

Total Holck (2007) F 24 18 17 59

M 24 24 30 78

137

TOTAL SAMPLE F 54 47 51 152

M 75 71 61 207

Total 359²

¹ Overlapping burials excluded after cross-calibration.

² 25 burials excluded after DXA-analysis.

Table 1. Demographic data skeletal sample included in the study. Reproduced from Brødholt, Günther et al. (2021).

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- 15 - I. The following section gives an overview of the procedures leading up to the analyses and the methods employed in the osteological analysis and DXA scanning.

ETHICAL CONSIDERATIONS

All investigations were performed in accordance with the Guidelines for Research Ethics in the Social Sciences, Humanities, Law, and Theology and Guidelines for Research Ethics on Human Remains issued by The Norwegian National Research Ethics Committees. Ethical approval was obtained from the National Committee for Research Ethics on Human Remains (2015/396 and 2016/304). Furthermore, all necessary permits were obtained for the described study, which complied with all relevant regulations.

The human remains were treated with due respect and handled with care. The choice of solely non-destructive analysis methods was based on the limited and invaluable nature of the human remains included in the study. All skeletal material was well documented and considered unproblematic regarding origin. Skeletal material with known identity and possible identifiable descendants, as well as skeletal material of Sami origin, were excluded from the study.

OSTEOLOGICAL DATA COLLECTION

All skeletal material included in the study underwent macroscopic analysis and evaluation of sex, age, stature, trauma, and pathologies prior to DXA analysis.

The Schreiner Collection database and archive literature provided osteological and contextual data on the skeletal remains. Complete osteological profiles of the skeletal material from the Late Iron Age and the Church of St. Mary were obtained from previous analyses by the authors (Brødholt, 2006, 2007a, 2007b, 2016; Brødholt & Holck, 2012). In addition, the skeletal material from the post-Reformation period, Christiania Tukthus and Tangen Church, underwent a complete osteological analysis. Osteological data on the skeletal material from Hamar Cathedral were

Fig. 2. The region of interest: the femur neck (collum femoris). Redrawn from Jmarchn, DXA femoral neck with osteoporosis, CC BY-SA 3.0

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- 16 - provided by Sellevold (2000); (2001), while data on the skeletal material from the Church of St. Clemens, St. Olav's Monastery, and Prestgardskirken (incorporated sample) were provided by Holck (2007) as well as The Schreiner Collection database and archive literature.

The osteological analysis was performed in accordance with methods given by Buikstra and Ubelaker (1994); the sexing of crania (Acsádi & Nemeskéri, 1970), the assessment of pelvic features (Phenice, 1969), the pubic symphysis (Brooks & Suchey, 1990; Todd, 1921), and the estimation of age-at-death was performed by evaluating suture closure as described by Meindl and Lovejoy (1985). The age groups Young Adult (20-35 years), Middle Adult (35-50 years), and Old Adult (50+) were applied, as per Buikstra and Ubelaker (1994). Pathology and trauma were registered according to Ortner (2003) and Aufderheide and Rodríguez-Martín (1998).

Stature was estimated according to Trotter and Gleser (1952); (1958).

DUAL-ENERGY X-RAY ABSORPTIOMETRY

A Lunar iDXA (GE Healthcare Lunar, Madison, WI, USA) was used for the BMD measurements. BMD was measured at the femur neck (collum femoris) as the loss of bone at this site is a good indicator of the risk of osteoporosis and fractures. Measurement of BMD at this site also facilitates comparison with previous examinations of bone loss in archaeological populations of Norway. If available, both femora from one individual were measured.

Normative data from the National Health and Nutrition Examination Survey III (NHANES III) were used as an international reference standard for describing osteopenia and osteoporosis in postmenopausal women and men over 50 years. The World Health Organization’s (WHO) definition of osteopenia by DXA is a BMD between -1.0 and -2.5 SD below the young female adult mean (young adult Caucasian women aged 20-29 years). A BMD equal to or lower than -2.5 SD is defined as osteoporosis (GE, 2014; Genant et al., 1999; Kanis, 2002; Kanis et al., 2008; WHO, 2007). For extensive details on the procedure, inclusion criteria, and cross- calibration, see paper I.

Soft tissue substitute

Due to the lack of soft tissue and bone marrow, the DXA analysis method was modified in order for it to be applied to archaeological specimens (Chappard et al., 2004; Lees et al., 1993).

A combination of water and plastic boards was used as a soft-tissue substitute. The weight was set according to estimated stature, and the soft tissue substitutes were adjusted to obtain the

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24.9 kg/m² (WHO, 2018).

Standardization

A specially constructed frame with plastic boards inside and a container of water on top was used and was created to allow the positioning of a femur between the boards and the water.

The water level in the container was set to 14.5 cm. The femur was positioned with the anterior surface facing up, with the neck in a horizontal plane and the diaphysis oriented parallel to the scanner's axis. An angled mirror in the proximal end facilitated the horizontal orientation of the proximal femur.

A QA (quality assurance) procedure was performed daily, using a calibration block consisting of tissue-equivalent material with three bone-simulating chambers of known BMD content. This daily QA procedure calibrated the machine and performed quality control measurements. A phantom, simulating L2–L5, was used as a separate control measure and quality control in addition to the QA (GE, 2014).

Validation of precision

Each femur in the DXA sample was scanned three times to assess the measurements' precision and repeatability. According to the manufacturer of the Lunar iDXA, the expected precision error for repeated measurement of femur BMD is ≤ 1.0% (% CV), or ≤ 0.010 g/cm² (GE, 2014).

The observed precision error in this study was 0.7% or 0.007 g/cm².

Incorporated skeletal sample and cross-calibration

The study adopted BMD data from the DXA analysis by Holck (2007), which were retrieved from the database associated with the Lunar Prodigy (GE Healthcare Lunar, Madison, WI), located at Lovisenberg Diakonale Hospital, Oslo. Seventy-one individuals with scans in accordance with the DXA analysis criteria were included in the study. These BMD values were cross-calibrated to reduce any systematic differences in average BMD measurements between scanners (see Brødholt, Günther, Gautvik, Sjøvold, and Holck (2021) for the Bland-Altman plot and further details). In addition, a control group was set up to assess the compliance of

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- 18 - measurements between these two studies. Fifteen femora from the Church of St. Mary, previously scanned with the Lunar Prodigy, were scanned with the Lunar iDXA.

STATISTICAL ANALYSES Paper I

A multivariate linear regression model was fitted to the complete dataset, with mean BMD as the dependent variable and time period, age group, age group, sex, and SES as independent variables. In this model, the effect on mean BMD was estimated simultaneously for all independent variables. The interpretation of the model is thus that the estimated effect of, e.g., the medieval period is the increase or decrease in mean BMD (g/cm²) compared to the Late Iron Age when the other explanatory variables remain constant, i.e., for the same sex, age and SES group. To compare the mean BMD between time periods for specific age groups for females or males or between age groups of females or males within a time period, we used a two-sample t-test. In addition, a one-sample t-test was applied to compare the mean BMD levels from the Late Iron Age, medieval and post-Reformation period samples to the modern reference values for each sex and age group (calculated from the manufacturer’s reference values for USA/Northern Europe (GE, 2014). When performing many statistical tests, the problem of multiple testing needed to be addressed. We applied the Benjamini-Hochberg procedure to control the false discovery rate at the 10% level, and thus comparisons with FDR q-value less than 0.10 were considered significant. The statistical analysis was performed using R (R Core Team, 2014).

Paper II

The variation in neck mean BMD and stature were modeled using linear regression. The distributions of neck mean BMD and stature were first visually inspected by histograms and QQ-plots and found to be approximately normally distributed. With neck mean BMD as the response variable, age group (Young, Middle, and Old Adult), sex, and SES (High-status burials and Parish population burials) were used as explanatory variables. When stature was the response variable, sex and SES group were the explanatory variables. Two sample t-tests were applied to compare the mean stature in the two SES groups and the mean BMD between SES groups for a specific age group for females or males. Model assumptions of independence

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- 19 - and normality were checked using residual plots. The analyses were conducted in R (R Core Team, 2014), and the boxplots were created using the package ggplot2 (Wickham, 2016).

Paper III

Two sample t-tests were used to test whether the stature differed significantly between the high status and parish population groups and whether the mean BMD or stature differed between the burial sites within each group. Pearson's chi-square test was used to test whether the proportion of osteopenia/osteoporosis was equal in the high-status and parish groups. The analyses were conducted in R (R Core Team, 2014), and the boxplots were created using the package ggplot2 (Wickham, 2016).

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SUMMARY OF RESULTS

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PAPER I

Brødholt, E. T., Günther, C.-C., Gautvik, K. M., Sjøvold, T., & Holck, P. (2021). Bone mineral density through history: Dual-energy X-ray absorptiometry in archaeological populations of Norway. Journal of Archaeological Science: Reports, 36, 102792. https://doi.org/:10.1016/j.jasrep.2021.102792

In paper I, we report long-term historical trends and patterns of BMD variation and age-related bone loss in males and females in Norway from the Late Iron Age, Medieval period, and post-Reformation Period. The observed BMD variation and bone loss were compared to the pattern observed in modern populations. Using osteological analysis and DXA, we present results of BMD measurements of 222 individuals from four burial sites representing the medieval and post-Reformation periods. Existing BMD data from 137 individuals dating to the Late Iron Age and the medieval Period were incorporated into the study. We found that mean BMD increased significantly from the Late Iron Age to the medieval period (p = 0.0002), followed by a significant decline from the medieval to the post-Reformation period (p = 0.014). Young medieval females had the highest mean BMD of all time periods, including the modern female population, and significantly higher mean BMD than young females from the Late Iron Age (p = 0.02;

q = 0.093). Overall, our results revealed a significant BMD variation through Norway's prehistoric and historical time periods. The patterns of age-related bone loss observed in the archaeological populations were diverse, with substantial temporal changes suggesting a transition towards a modern pattern. The bone loss often exceeded that observed in the population today.

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PAPER II

Brødholt, E. T., Gautvik, K., Günther, C.-C., Holck, P., & Sjøvold, T. Social stratification reflected in bone mineral density and stature: Spectral imaging and osteoarchaeological findings from medieval Norway (under review).

In paper II, we demonstrated a significant difference in BMD related to SES by examining skeletal remains from five burial sites in medieval Norway. Results from DXA-analysis and osteological analyses were seen in relation to SES and estimated stature. We detected that socioeconomic status significantly affected bone mineral density and stature. Individuals of high status had higher bone mineral density (0.07 g/cm^², p = 0.003) and taller stature (1.85 cm, p = 0.017) than individuals from the parish population. We detected no significant relationship between young adult BMD and SES. For males, high young adult BMD and stature varied concordantly in both status groups, while females of high status were significantly taller than females in the parish population. The age-related pattern of bone variation also demonstrated quite different trajectories for the two SES groups for both sexes. We discussed sociocultural practices possibly explaining these differences in BMD related to SES, demonstrating the impact of living conditions and nutrition on growth and skeletal development. Overall, our results indicate that femur neck BMD may be a valuable skeletal indicator of SES.

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PAPER III

Brødholt, E. T., Gautvik, K., Benedictow, O. J., Günther, C.-C., Sjøvold, T., & Holck, P. Female skeletal health and socioeconomic status in Medieval Norway (11th-16th centuries AD): analysis of bone mineral density and stature (under review).

In paper III, we showed the impact of SES on female skeletal health and the occurrence of osteopenia and osteoporosis at five burial sites in medieval Norway. We compared results from DXA-analysis and osteological analyses to the SES of 101 females.

Previous research by the authors (Paper II) prompted us to investigate whether SES differences in the medieval population of Norway had a greater impact on female health. We investigated female bone loss in relation to SES and whether young adult femur neck BMD and estimated attained stature could be used as skeletal indicators of SES. We found that the parish population females had a significantly higher occurrence of osteopenia and osteoporosis in old adulthood (p = 0.003). Young adult females of high status were taller than parish population females (5.3 cm, p = 0.01), while their femur neck BMD did not differ significantly between the two status groups (p = 0.127).

We hypothesize that the lower attained young adult BMD in parish population females, combined with accumulated negative environmental influences during adult life, resulted in earlier onset of osteoporosis and increased bone loss by old adulthood.

Altogether, our findings demonstrated a pattern of bone loss in our SES groups possibly related to the attainment of BMD in young adulthood.

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DISCUSSION

LONG-TERM HISTORICAL VARIATION AND PATTERNS Temporal trend in BMD

Research on archaeological skeletal material from Norway (Holck, 2007; Mays et al., 2006;

Turner-Walker, Syversen, et al., 2000; Turner-Walker et al., 2017) has focused mainly on the medieval period and led to few conclusive results regarding long-term trends, patterns and changes from prehistoric to modern times. In paper I, we examined the long-term historical trend regarding BMD over the course of three archaeological time periods (8th – 19th centuries AD) in Norway and compared our findings to the modern population (Table 2). Our results showed that mean BMD increased significantly from the Late Iron Age to the medieval period (p= 0.0002). This was followed by a significant decline from the medieval to the post- Reformation period (p= 0.014). The overall results revealed significant BMD variation and substantial temporal changes through Norway's prehistoric and historical time periods.

Compared to modern reference levels, young adult females in the medieval period had higher mean BMD (p = 0.02, q-value 0.13), while the middle adult males in the Late Iron Age and old adult males in the post-Reformation period showed lower mean BMD (p = 0.01, q-value 0.12 and p = 0.01, q-value 0.12, respectively). However, none of these results were significant after adjusting for multiple testing. Few previous research studies and the lack of BMD data in consecutive archaeological populations rendered it difficult to contextualize our results. We interpreted the observed variation as the result of the interplay of complex and exogenous variables influencing BMD in these specific populations, which require further investigation in a broader context.

LIA MP PRP M

n BMD g/cm² SD % n BMD g/cm² SD % n BMD g/cm² SD % BMD g/cm² %

F Young Adult 11 0.936 0.12 100 26 1.051 0.14 100 12 0.991 0.19 100 0.985 100

Middle Adult 4 0.825 0.12 88 31 0.901 0.20 86 5 0.967 0.14 98 0.943 96

Old Adult 2 0.830 0.20 89 44 0.830 0.15 79 2 0.816 0.04 82 0.843 86

M Young Adult 7 1.099 0.19 100 49 1.116 0.17 100 9 1.057 0.13 100 1.080 100

Middle Adult 12 0.905 0.13 82 38 1.039 0.14 93 9 0.985 0.14 93 1.020 94

Old Adult 12 0.929 0.14 85 39 0.959 0.15 86 4 0.856 0.03 81 0.940 87

F= females, M= males. LIA= Late Iron Age, MP= Medieval period, PRP= post-Reformation period, M= modern.

Table 2. Summary overview of the skeletal material presented by femur neck BMD values per sex, age, and time period. BMD is also given in percent of the Young Adult value. Reproduced from Brødholt, Günther et al. (2021).

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- 25 - The two previous studies investigating temporal BMD variation in Scandinavian skeletal material (Bennike & Bohr, 1990; Holck, 2007) detected an inconsistent pattern of BMD variation. Bennike and Bohr (1990) examined skeletal material from the Neolithic to the medieval period (4200 BC – 1536 AD). They found the highest values (bone mineral content in the femur diaphysis, dual photon absorptiometry) in the Neolithic and the lowest in the medieval period. Compared to modern autopsy cases, the values in these time periods were significantly higher and lower, respectively. These findings were not further discussed by the authors but were later interpreted by Poulsen et al. (2001, p. 456) as a lack of support for the hypothesis of "a consistent millennial trend toward lower BMD in the Scandinavian population." Holck (2007) found no significant differences in mean femur neck BMD between the prehistoric (5000-1800 BC), Viking age (800-1050 AD), and medieval material (1050-1536 AD) from Norway (p = 0.151). Only the medieval bones (sexes combined) showed a significantly higher mean BMD than the modern reference population (p = 0.001). The results were interpreted to indicate similar physical strains and life struggles experienced in these time periods.

Other studies on skeletal material from Scandinavia have measured BMD limited to a single time period and compared these values to the contemporary population. Ekenman et al.

(1995) examined skeletal material from medieval Stockholm, Sweden (1300-1530 AD) and detected slightly higher bone density (femur diaphysis, radiographic and dual photon absorptiometry) in men compared to modern-day Stockholm. However, no difference was seen in women. The higher BMD in medieval men was interpreted as being caused by daily physical activity, including frequent standing and walking. Poulsen et al. (2001) examined skeletal remains from the medieval village of Nordby, Denmark (femoral neck, DXA). The results revealed that medieval men of all ages had significantly higher BMD (p = 0.02) than contemporary males. This difference was explained by men's higher level of physical activity as compared to modern-day men. Women had significantly lower BMD than modern females (p = 0.04); however, this finding was reversed for older women. This result was interpreted as being related to fertility and reproductive factors. Overall, previous studies describing long- term historical variation and patterns have demonstrated diverse and inconclusive results.

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- 26 - Temporal age-and sex-related BMD variation

The femur neck mean BMD values calculated for each sex, age group, and time period in paper I revealed a diverse pattern and substantial temporal changes. The age-related patterns of bone loss in both sexes in the Late Iron Age were characterized by marked early bone loss (from young to middle adulthood) but only significant for males (p = 0.03, q-value 0.09). In the medieval period a significant early bone loss occurred in both sexes (p = 0.0014, q-value 0.025 in females and p = 0.02, q-value 0.09 in males), while significant late bone loss (from middle to old adulthood) was observed exclusively in males (p = 0.017, q-value 0.09). Both sexes in the post-Reformation period experienced minor early bone loss followed by marked late bone loss (significant only in males, p = 0.03, q-value 0.09). The temporal pattern and variation were novel observations that lack parallel in previous research on archaeological populations, rendering it challenging to contextualize our results. We interpreted the results to indicate that the age- and sex-related pattern of bone loss shifts towards a more modern pattern characterized by marked bone loss late in life. This transition may be related to societal and/or economic changes, such as improved living conditions, increased life expectancy, and an altered reproductive pattern.

Early (pre- or peri-menopausal) bone loss in females, such as that observed in the Late Iron Age and medieval period in our study, are observed and discussed in several previous studies (Agarwal & Grynpas, 1996; Curate, 2014; Mays, 2008) and has led to the hypothesis that age-related bone loss in females started earlier in archaeological time periods than today.

This pattern is often in connection with a different practice regarding the onset of childbearing, characterized by high parity and late weaning compared to the modern-day population (Mays et al., 2006; Turner-Walker, Syversen, et al., 2000; Turner-Walker et al., 2017). Curate and Tavares (2018, p. 233) argued that BMD in young females should be viewed as a complex trait resulting from the "interplay between reproductive factors, genetics, nutrition, physical activity and age at menarche." Studies on bone loss in archaeological populations of Scandinavia discussed the stresses of pregnancy and lactation in relation to insufficient nutrition (Holck, 2007; Mays et al., 2006; Poulsen et al., 2001; Turner-Walker et al., 2017). In this study, the early bone loss observed in males from the Late Iron Age and medieval period is remarkable and has few parallels in the archaeological record. This phenomenon is difficult to explain without further examination of specific risk factors pertaining to these populations and time periods. The early bone loss in both sexes from this time period could indicate that the factors influencing BMD also affected health in the general population. We hypothesized that such a

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- 27 - pattern of early bone loss could be related to a shorter life expectancy (Mays et al., 1998; Mays, 1996), arduous work, poor nutrition, and generally demanding living conditions.

To our knowledge, the pattern of late (postmenopausal) bone loss observed in females from the post-Reformation period in our study, similar to the pattern observed in modern populations, has never been described previously in archaeological skeletal material from Norway. However, this pattern of bone loss in females has been reported in a number of examinations of prehistoric and historic skeletal material (Hammerl et al., 1991; Kneissel et al., 1994; Lees et al., 1993; Mays, 2006). Minor peri- or premenopausal and pronounced postmenopausal bone loss in females were discussed in relation to a higher degree of physical activity, possibly combined with the effect of parity in conserving bone mass (Lees et al., 1993). In our study, the males from the medieval and post-Reformation periods exhibited late bone loss similar to that observed in the modern population. However, the medieval males also experienced early bone loss, which was an unprecedented finding. Mays et al. (1998) described a comparable pattern of late bone in males, similar to or even exceeding that observed in modern populations, and argued to support the hypothesis that lifestyle factors may be less imperative than previously thought. The similarity in the pattern of bone loss between the medieval and modern populations was surprising in light of the notion that lifestyle factors are widely held to influence the severity of bone loss. We believe that the pattern of late bone loss in males from the medieval and post-Reformation periods in our skeletal sample results from multiple factors influencing BMD and bone loss in these periods compared to the Late Iron Age. Some of these factors are yet to be identified.

USE OF BMD AS A SKELETAL INDICATOR OF SES

In paper II, we revealed that the extensive social stratification present in the medieval period in Norway was reflected in BMD variation as detected in measurements of skeletal remains from five representative burial sites. Individuals from the parish population showed significantly lower BMD than individuals of high status, affecting both males and females (Table 3). These results indicated that femur neck BMD might be a valuable skeletal indicator of SES.

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- 28 - Patterns of BMD variation across the adult life span

Males

The patterns of age-related bone loss observed in males in the two SES groups differed. The parish population group appeared to follow a modern trajectory, as the age-related bone loss for males in this group followed the same pattern as modern-day males, with minor early followed by significant late bone loss (GE, 2014). We documented a similar pattern of age- related bone loss in paper I in a high-status population from the post-Reformation period in Norway. It was likely the result of multiple factors, some of which are unidentified. Mays et al. (1998) detected a significant late bone loss for males from medieval Wharram Percy, England, similar to or even exceeding that observed in modern males. The authors interpreted the results to indicate that lifestyle factors were less important in relation to bone loss than previously assumed.

Interestingly, the marked early bone loss detected in high-status males in paper I and further discussed in paper II are rarely observed in the archaeological literature. We remarked that this bone loss is similar to that detected in parish females from young to middle adulthood and suggestive of distinct environmental stresses or factors in the two groups during this life phase. We assumed that the high social status of these males entailed good housing conditions, access to a varied and wholesome diet, and better sanitary conditions. Their status probably led to a more sedentary life, which could lead to activation of bone loss. Their lifestyle risk factors increased the risk for “modern diseases” such as metabolic syndrome and diabetes 2. Research on alcoholism in medieval England showed that excessive consumption of alcohol was widely spread in all classes of society but prevailed among the clergy and university students ("Alcoholism in Medieval England," 1933). In paper I, we detected significant early bone loss

High status Parish population Modern*

n BMD g/cm² SD %** n BMD g/cm² SD %** BMD g/cm² %**

FEMALES YA 12 1.094 0.09 100 14 1.014 0.16 100 0.985 100

MA 9 0.898 0.15 82.2 22 0.902 0.22 89 0.943 96

OA 4 0.975 0.07 89.1 40 0.815 0.15 80.4 0.843 86

MALES YA 17 1.185 0.19 100 32 1.08 0.14 100 1.08 100

MA 18 1.046 0.13 88.3 20 1.033 0.15 95.6 1.02 94

OA 15 0.998 0.15 84.2 24 0.935 0.15 86.6 0.94 87

* Reference value for USA/Northern Europe (GE, 2014).

* The age-related changes are given as percent of the mean BMD in the Young Adult age category.

Table 3. Femur neck BMD values per sex, age and SES-group in medieval sample as well as modern BMD values. Reproduced from paper II (Brødholt, Gautvik, Günther, Holck, & Sjøvold).

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- 29 - (p = 0.03, q = 0.09, two-sample t-test, Benjamini-Hochberg procedure) in males in a skeletal material dated to the Late Iron Age in Norway. This early bone loss was followed by a slight increase in BMD from middle to old adulthood. Many of these burials were considered characteristic of the upper social strata at the time. A shorter life expectancy and generally demanding living conditions were considered possible explanatory factors.

The degree of late bone loss in high-status males was markedly less than that observed in parish males and modern men, possibly indicating more favorable conditions for elderly males of high social status than for elderly males in the parish population. This could entail better housing, dietary practices, and the ability to pay for provent and care in old age.

Interestingly, the overall reduction in BMD by old adulthood appeared rather similar for males in our two status groups and comparable to the bone loss observed in modern men by old adulthood.

Females

We detected that females in the two SES groups also portrayed different trajectories regarding the age-related reduction in BMD: the high-status females displayed distinct early bone loss followed by an increase in BMD, while the parish females displayed a non-distinct and similar decrease in BMD early and late in life. Marked early bone loss has been linked to the nutritional strain of childbirth and lactation, so-called reproductive stress (Holck, 2007; Mays, 2006;

Poulsen et al., 2001; Turner-Walker et al., 2017), although a strict reproductive interpretation should be avoided (Curate, 2014). Such pre- or peri-menopausal bone loss, as evident in the high-status females, was observed in several previous studies of archaeological populations (Agarwal & Grynpas, 1996; Mays, 2008; Mays et al., 2006; Turner-Walker, Syversen, et al., 2000; Turner-Walker et al., 2017). Compared to the modern population, the onset was earlier than today, the parity was high, and the lactation period was prolonged (Agarwal & Grynpas, 1996; Curate, 2014; Holck, 2007; Mays, 2008; Mays, 2006; Turner-Walker, Syversen, et al., 2000; Turner-Walker et al., 2017). Most epidemiological studies documented a transient decrease in BMD connected to pregnancy and lactation (Curate & Tavares, 2018; Karlsson, Ahlborg, & Karlsson, 2005). Interestingly, first pregnancy in adolescence and a shorter reproductive lifespan between menarche and menopause were associated with reduced BMD (Stride, Patel, & Kingston, 2013).

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- 30 - In paper II, we interpreted the marked early bone loss in high-status females as an indication of a greater depletion of bodily resources in this phase of life, perhaps linked to (at least partly) early and multiple pregnancies. It is possible that a more sedentary lifestyle, with considerable less physical activity among high-status females, resulted in or contributed to a delayed recovery after each pregnancy. The parish population females likely experienced demanding physical labor connected to everyday activities. This hard labor may have reduced the bone loss accompanying pregnancy. Lees et al. (1993) linked the non-significant premenopausal bone loss in parish females buried at Christ Church, Spitalfields (18-19^th century London) to a high level of physical activity, both at work (weaving industry) and outside (walking), coupled with the bone conserving effects of parity. The pattern of late rather than an early bone loss in women is not a recent trait. It has been described in skeletal material from the Early Bronze Age (4000 BP) in Austria (Kneissel et al., 1994), in a 3^rd- 4^th century CE population from Ancaster, England (Mays, 2006), and in a Merovingian population (5^th – 7^th century CE) from Bockenheim, Germany (Hammerl et al., 1991).

We also compared mean BMD between SES groups for each specific gender and age group (paper II) and could only detect a significant difference between old adult females: the high-status females showed a significantly higher mean BMD than parish females. We suggested that the increased BMD in elderly females in the high-status group could reflect nutritional and lifestyle factors influencing BMD already from an early age. High-status females had favorable living conditions, enabling them to recover from years of multiple pregnancies and depletion of bodily resources to a much larger degree than the parish population females. They could also pay for upkeep and personal care in old age and probably had the means to enjoy a varied and nutritious diet.

Early life conditions

The development of an individual's maximal bone mass (PBM) is 60–80 % genetically determined (Nguyen et al., 1998; Weaver et al., 2016) but is modified by both pre- and post- natal determinants, e.g., nutrition, vitamin supply, and presence of chronic diseases. The most rapid skeletal growth occurs within two years after birth, and a second skeletal growth burst corresponds to puberty. Thus, our age-dependent bone mass is influenced by several variables such as sex, nutrition, endocrine factors, mechanical strain, disease, and exposure to risk factors, while PBM is predominantly genetically determined (Bonjour et al., 1994; Khosla &

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Bone mineral density in archaeological populations of Norway: Temporal patterns of bone loss related to age, sex, and socioeconomic status in the 8th - 19th centuries AD