Prevalence of child stunting in Sub-Saharan Africa and its risk factors

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Review

Prevalence of child stunting in Sub-Saharan Africa and its risk factors

Siri Hundstad Quamme

^a

, Per Ole Iversen

^a^,^b^,^c^,^*

aDepartment of Nutrition, University of Oslo, Oslo, Norway

bDepartment of Haematology, Oslo University Hospital, Oslo, Norway

cDivision of Human Nutrition, Stellenbosch University, Tygerberg, South Africa

a r t i c l e i n f o

Article history:

Received 16 October 2021 Accepted 31 January 2022 Available online 4 February 2022 Keywords:

Children Environment Food insecurity

Linear growth impairment Maternal empowerment Southern Africa

s u m m a r y

Background&Aims:Child stunting (impaired height-for-age) is a marker of chronic undernutrition and results from insufﬁcient energy and nutrient uptakes. Stunting has severe consequences for future physical and mental development. A WHO target is to reduce the prevalence of stunting by 40% within 2025. In contrast to other parts of the world, stunting has been a major public health problem in many African countries for a long time. Here we present a narrative review on stunting during the last 20 years among children5 years in Sub-Saharan Africa (SSA), where stunting is rampant.

Methods:We identiﬁed 13 articles from 2000-2020 based on pre- deﬁned criteria.

Results:Children in SSA are highly affected by stunting, with an average prevalence of 41%. Stunting is signiﬁcantly higher in children>1 year, in boys, in low birth weight, in shorter interpregnancy interval, in mothers with lower education, and in poor and food insecure households. Maternal education, feeding practices and environmental factors (e.g. climate change) are important risk factors.

Conclusions: Although the prevalence of stunting has been reduced over the last two decades, great effort remains to reach the global target. Policies and interventions should target

Abbreviations:BCG, Bacillus CalmetteeGuerin; DHS, Demographic and Health Survey; DTP1, Diphtheria, pertussis, and tetanus; DRC, Democratic Republic of the Congo; MV, Measles virus vaccine; SDG, Sustainable Development Goal; SSA, Sub- Saharan Africa.

*Corresponding author. Department of Nutrition, P.O. Box 1046 Blindern, 0317, Oslo, Norway.

E-mail addresses:[email protected](S.H. Quamme),[email protected](P.O. Iversen).

Contents lists available atScienceDirect

Clinical Nutrition Open Science

jo u r n a l h o m e p a g e :

w w w . c l i n i c a l n u t r i t i on o pe n s c i e nc e . c o m

https://doi.org/10.1016/j.nutos.2022.01.009

2667-2685/©2022 The Author(s). Published by Elsevier Ltd on behalf of European Society for Clinical Nutrition and Metabolism. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

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education for women, child feeding practices and environmental factors including climate change.

creativecommons.org/licenses/by/4.0/).

1. Introduction

Stunting, i.e. impaired linear growth-for-age, is usually deﬁned as two standard deviations or more below the WHO Child Growth Standards median [1]. The condition occurs primarily when the child's dietary intake is deﬁcient in energy and nutrients essential for growth and development [1]. It is a marker of chronic undernutrition that affects millions of children across the globe and poses a great risk to their health and future. For example, stunted compared to non-stunted children have higher mortality rates and are more likely to die from diseases like diarrhea, pneumonia, malaria, and measles [2]. Stunting is also more likely to affect children exposed to infections, in poor households and in children of mothers with poor diets prior to and during pregnancy [3]. Long-term consequences may include limited cognitive development, lower education level and subsequently lower work-wages [4].

Furthermore, the risk of overweight and non-communicable diseases later in life is increased, contributing to the double burden of malnutrition [5e7].

Pertinent to the challenge of malnutrition in all its forms, are the declarations issued by the UNs specialized agencies stating the universal right to food. Article 25 of The Universal Declaration of Human Rights states the right to an adequate standard of living, which ensures health and well-being, including food [8]. Article 24 of The Convention on the Rights of the Child specifies children's right to the highest attainable standard of health [9]. It emphasizes the importance of combatting disease and malnutrition through the provision of adequate foods. Article 24 also points out that one must consider the impact of environmental pollution, which affects food security. To grasp the magnitude of these problems, in 2019, it was estimated that 21.3% (144 million) of all children underfive years were stunted, 36% of them living in Sub-Saharan Africa (SSA) and Southern Asia [5,10]. From 2012 to 2019, the prevalence of stunting in SSA decreased from 34.5% to 31.1%, however not at a sufficient rate to meet the global target [5]. When considering the absolute number of children rather than percentage, SSA is in fact the only sub-region that has seen a rise in child stunting in the recent years [5].

To combat the issue of child stunting, the WHO and UN have set targets for development in nutrition status. The WHO has defined six global nutrition targets, one of which aims to reduce the number of children under the age offive who are stunted by 40% within 2025 [1]. In 2015, the UN Member States agreed on 17 Sustainable Development Goals (SDGs) to be reached by 2030. The second goal is to achieve zero hunger. More specifically, to“end hunger, achieve food security and improved nutrition and promote sustainable agriculture”[10]. SDG2 is further specified in several targets. One of them is to reduce the number of stunted children underfive years of age to 100 million by 2025 and to 83 million by 2030 [10]. To reach these targets through interventions and policies, it is essential to know what factors contribute to the risk of stunting. Previous studies have identified several possible risk factors, whereby some relate to the mother, some to the child and some to the child's household and environment [11,12]. Some studies have found that the risk of stunting is already affected by the mother's nutritional status before conception, and therefore suggest targeting women in reproductive age and pregnant women [13]. Other studies suggest interventions directed towards the child directly, for instance through infection treatment and provision of supplements [14]. As nutrition status is dependent on food access and food security, stunting prevalence may also be determined by household wealth, agricultural practices, political situation, and climate [15e17].

There is a paucity in compiling data of over time in child stunting in SSA, where stunting continues to be a rampant public health concern. Such information might be important, not only for the child's household members, but also for health personnel and other stake-holders and policy-makers. To address this knowledge gap, we here provide a narrative review to assess the prevalence of stunting in

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children in SSA under the age ofﬁve years, a critical period for growth and development including the transition from breast-feeding to complementary feeding. The second aim was to review risk factors of childhood stunting in this area to propose possible targets for interventions.

2. Materials and methods 2.1. Literature search

We decided to present our research as a narrative review. In line with this, our review provides an updated, focused overview of our chosen topic, and not an exhaustive review of all available literature.

Thus, a narrative review will be shorter and more concise compared with e.g. a systematic review or meta-analysis.

For this review, a structured literature search was conducted in the database PubMed. We wanted to identify original studies on the prevalence and risk factors of stunting among children underfive years of age in SSA, and the search was not limited to any particular study design, hence e.g. randomized trials and observational studies were eligible for inclusion. We did not include reviews or meta-analysis in the selected literature-search, however we did include other reviews and meta-analysis when discussing ourfindings. The search was conducted on March 1^st2021 and later repeated on October 1^st, 2021, however no additional studies were identified in the latter search. Using the Population, Expo- sure, Comparator and Outcomes (PECO) framework as a guideline, the following search combination of MESH words was formed:“(stunting OR undernutrition) AND under five AND Sub-Saharan AND prevalence”. As we wanted to identify novel areas of research, risk factors or exposures were not specified in the search.

2.2. Study-article selection

The studies were selected according to the following pre-defined criteria¶: The studies had to be written in the English language and be published in a peer-reviewed journal between the years 2000 and 2020. The studies also had to use the WHO definition of stunting, i.e. a height-for-age two standard deviations or more below the WHO Child Growth Standards median. The study area was limited to countries in SSA, which consists of 46 countries below the Sahara desert, as defined by the UNs Sta- tistics Department [18]. Studies that examined both single and multiple countries in SSA could be included. Furthermore, the study variables included the prevalence of stunting and/or the size of risk factors of stunting. Studies on stunting as a risk factor for other outcomes, for instance anemia or mortality, were not included.

2.3. Ethical approval and informed consent

Neither the Institutional Review Board of Stellenbosch University nor the Norwegian Regional Committee for Medical and Health Research Ethics require ethical approval and informed consent because our study is a review of published literature.

3. Results

3.1. Identiﬁed studies

The structured literature search identiﬁed in total 46 studies, of which 13 studies met the inclusion criteria. We present the selection process using theﬂowchart inFig. 1. Some studies were excluded because they examined wasting or overweight, and some were developing or testing a statistical model. Overall, the included studies covered 36 of the 46 sub-Saharan countries in Africa. More studies were from countries in East Africa than in the South, the West, and in Central Africa. Five of the studies assessed the prevalence of stunting in areas within a country, two studied a country as a whole, whereas six studies included multiple countries, 35 at the most.

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3.2. Data sources

Some studies conducted surveys and obtained anthropometric measurements independently, whereas most studies analyzed data from national Demographic and Health Surveys (DHSs). The DHSs are routinely conducted in several countries to monitor populations and their health and nutrition status. Depending on which country the survey is conducted in and what speciﬁc challenges that country faces, the survey can be adapted to include questionnaires on for instance malaria, women's status and domestic violence [19].

3.3. Prevalence of child stunting

The prevalence of stunting among children underﬁve years in Sub-Saharan Africa is still high (Table 1). A study covering 33 countries found an average prevalence of 41.1% (20). The highest prevalence was found in East and Central Africa, whereas the southern countries had the lowest prevalence [21,22].

One Eastern country with a particularly high prevalence was Burundi: Berendsenet al.found a prevalence of 58.3% whereas more recent studies reported about 55% [20e22]. The lowest prevalence was found in Senegal [21]. Two studies from Addis Ababa and Wolayta Sodo Town in Ethiopia reported a prevalence of about 20% [23,24] These were both from urban settings. A 2015 study estimated that over a third of children underﬁve years in two districts in Uganda were stunted [25]. In Rwanda and

Fig. 1.Flow chart illustrating the selection of study articles.

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Table 1

Summary of studies and the results on prevalence and risk factors of stunting among children aged 0e60 months in Sub-Saharan Africa.

Author Age Study site and

sample size

Prevalence of stunting

Risk factors of stunting Narrative summary of results OR (95% CI)

Berendsenet al.

2016 (20)

1e60 months 33 countries Total: 41.1%

Nigeria 39.2%

Ethiopia 50.8%

DRC 43.4%

Highest: Burundi 58.3%

Lowest:

Gabon 21.0%

Reduced risk if child received vaccine against BCG before 1 month old OR 0.92 (0.89e0.94), DPT1 before 1 months OR 0.73 (0.68e0.77) and MV before 6 months OR 0.78 (0.71e0.82). Increased risk if child received vaccine against BCG after 3 months old OR 1.64 (1.53 e1.76), DPT1 after 7 months OR 1.32 (1.24e1.41) and MV after 12 months OR 1.13 (1.08e1.19).

in SSA 368,450

Berhaneet al.

2020 (23)

<60 months Addis Ababa 19.6% Increased risk if motherﬁnished grade 9e12 vs. college OR 1.46 (1.19e1.80), in severely food insecure households OR 1.42 (1.14e1.76) and if the child was male, OR 1.22 (1.06e1.39). No signiﬁcance in household wealth.

in Ethiopia 5,822

Ekholuenetale et al.2020 (21)

<59 months 35 Countries 384,747

West 33.9% Increased risk if mother had no education (concentration index -0.0990, p<0.001), among the poorest (concentration index

-0.1032, p<0.001) and, independently of education and wealth, among rural households (p<0.001).

Central 37.8%

East 35.3%

South 26.5%

Highest: Burundi 54.6%

Lowest: Senegal 19.1%

Esheteet al.

2017 (24)

6e59 Wolayta Sodo

Town, Ethiopia 315

22.2% 3.8% of which severely stunted

Reduced risk if literate mother OR 0.37 (0.19e0.74), child's age 24e59 months OR 0.36 (0.17-0-77) and household wealth in the 5^thquintile OR 0.28 (0.20 e0.77). No signiﬁcance in mother's employment or age.

Gebremedhin et al.2015 (32)

<59 months 25 Countries in SSA

213,889

- Increased risk if multiple births, that is twins or more OR 1.83 (1.70e1.97).

Habaasaet al.

2015 (25)

<59 months Nakaseke and Nakasongola districts, Uganda, 104

38.5% Reduced risk in pastoralist mothers compared to peasant mothers, OR 0.12, p¼0.05.

No signiﬁcance in child's age or sex, mother's age, her education or marital status or birth interval.

Magadiet al.

2011 (31)

<59 months 18 Countries in SSA

55,749

- Increased risk in HIVþmothers OR 1.28 (1.16e1.42). Also increased in children

>1 year, male children, in multiple births, higher birth order, shorter birth interval, small birth size, if no breastfeeding or breastfeeding>6 months, in rural household, poor household, if mother had no education, if mother's age was 15e19 years old, if less HIV in the community and if GDP per capita was low.

McKennaet al.

2019 (29)

6e59 months DRC 3,721

35.2% Increased risk if the mother did not take part in decisions regarding her husband's income in western provinces of DRC, OR 1.28 (1.00e1.63). Joint decision about husband's income or not taking part in the decision as compared to the mother deciding alone, increased (continued on next page)

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Mozambique, the prevalence was also high, at almost 40% [26,27]. In a study conducted in Kenya, almost half of the children were stunted, and about half of these were severely stunted [28]. Because many of these countries have large population sizes, Ethiopia being the most populated in the region, they contributed greatly to the burden of child stunting. On average, 35.3% of East African children underﬁve years were stunted [21].

In Central Africa, two studies focused mainly on the Democratic Republic of the Congo (DRC). A 2019 study found that the prevalence was just above 30%, however the DHS upon which the study was based was from 2008 [29]. In more recent studies, the prevalence was closer to 50% (20,30). An average of 37.8% of Central African children underﬁve years were stunted [21]. The data obtained from western SSA were exclusively from DHS-based studies. In Cameroon, the prevalence of childhood stunting was approximately 30%, whereas in Nigeria, the prevalence was just above 40%. Nigeria is the study region's most populated country and therefore contributed largely to the overall burden of child stunting in SSA. On average, 33.9% of West African children underﬁve were stunted [21]. Southern Africa was the region with the lowest prevalence of stunting, with an average of 26.5% [21].

Table 1(continued)

Author Age Study site and

sample size

Prevalence of stunting

Risk factors of stunting Narrative summary of results OR (95% CI)

the risk, OR 1.59 (1.06e2.40) and OR 1.71 (1.14e2.57), respectively.

Increased risk in male children, children 1 year, birth interval<23 months, mothers with no education, mother's older than 15e19, in rural and in poor households.

Nshimyiryo et al.2019 (27)

<59 months Rwanda 3,594

38% Increased risk in male children, children

>6 months, birthweight<2.5 kg,

mother's height<145 cm, mothers with no education, no intake of parasite drugs during pregnancy and in poor households.

No signiﬁcance in highland households.

Ntoimoet al.

2014 (30)

<59 months Cameroon 5,053

Cameroon 32% Increased risk among non-widowed, single mothers in Cameroon and DRC, OR 1.79 (1.16e2.74) and 1.69 (1.19 e2.41), respectively. No signiﬁcance when controlled for economic and parental resources and health behaviour. No signiﬁcance in widowed mothers.

Nigeria 18,823 Nigeria 41%

DRC 3,777 DRC 44.5%

Olacket al.

2011 (28)

6e59 months Kenya 1,245

47% (44.2e49.8) Severely stunted:

23.4% (21.0e25.8)

Higher prevalence of stunting among boys (p<0.01) and children aged 36e47 months (p<0.01).

Renzaho, 2007 (26)

6e59 months Mozambique 874

37% (95% CI 33.8 e40.2)

Higher risk among current food aid beneﬁciaries, OR 1.57 (1.01, 2.43).

No signiﬁcance in child's age or sex, household size or if never been beneﬁciary of food aid.

Yayaet al.2020 (22)

<59 months 34 countries in SSA

299,065

Highest in Burundi 54.6%.

Increased risk if inter-pregnancy interval<24 months as compared to the recommended 24e36 months, OR 1.26 (1.21e1.31). Decreased risk if inter-pregnancy interval 37e59 months or>60 months, OR 0.88 (0.85 e0.91) and 0.74 (0.71e0.77), respectively.

Lowest in Ghana 19.2%.

Highest in Central and East Africa.

Lowest in the South.

OR: Odds ratio, CI: Conﬁdence interval, BCG: Bacillus CalmetteeGuerin, DPT1: Diphtheria, pertussis, and tetanus, MV: Measles virus, DRC: Democratic Republic of the Congo, GDP: Gross Domestic Product.

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3.4. Risk factors for child stunting

The studies covered a broad range of risk factors including child characteristics, factors relating to the pregnancy, mother's characteristics, her education and employment, her empowerment and household wealth.

3.4.1. Age

Five out of seven studies examining the role of child age found a higher risk among children who were no longer infants. One study in Rwanda reported higher risk in children aged 6 months or older, while a study in the DRC reported a higher risk in children aged 1 year or older [27,29]. The latter result was also found in a study from 18 different countries in SSA [31]. Olacket al.found the highest risk among children in the age group 36e47 months in Kenya [28]. In Ethiopia, the age group 24e59 months was the least stunted [24]. Overall, the highest prevalence of stunting was among children between one and four years of age.

3.4.2. Gender

Boys were at a greater risk for stunting than girls. This was found inﬁve out of seven studies examining gender [23,27e29,31]. The remaining two studies considering gender and conducted in Uganda and Mozambique, found no signiﬁcant difference [25,26].

3.4.3. Pregnancy, birth, and medical treatments

A higher number of children underﬁve years in the same household increased the risk of stunting according to several studies. For example, two studies found an increased risk in multiple births [31,32].

One study found an elevated risk in having three or more children underﬁve years in the same household [29]. Moreover, in three out of four studies on the effect of interpregnancy intervals, an interval shorter than the recommended 24e36 months increased the risk of stunting [22,29,31]. This was further supported by Yayaet al.in 2020, who discovered that intervals longer than the recom- mendation decreased the risk [22].

Birth size was examined in two studies that both found a smaller birth size to increase the risk of stunting [27,31]. In Rwanda, not taking deworming drugs during pregnancy, i.e. drugs to reduce hel- minth and parasite infections, led to a higher risk [27]. Berendsenet al.conducted in 2016 a large study on the effect of vaccine timing [20]. The vaccines studied were the Bacillus CalmetteeGuerin (BCG) against tuberculosis, the combination vaccine against diphtheria, pertussis, and tetanus (DTP1) and the measles virus vaccine (MV). Children receiving the BCG vaccine before the age of 1 month, the DTP1 vaccine before 1 month and MV before 6 months, had a reduced risk of stunting. Interestingly, receiving the BCG vaccine after the age of 3 months, DTP1 after 7 months and MV after 12 months, increased the risk. For all three vaccines, a turning point in time was found where the vaccine shifted from decreasing to increasing the risk of stunting. Whether the current covid-19 pandemic and/or the introduced vaccines will affect stunting, remains to be examined.

3.4.4. Maternal education and empowerment

The mother's education level, work situation and decision-making power, also played a role in child stunting. The children of mothers with no education were found to be at greater risk in four studies, and one study reported an increased risk in mothers who hadfinished grade 9e12 as compared to finishing college [21,27,29,31]. A study in Uganda found no significant effect of education level;

however the same study found a reduced risk in children of pastoralist mothers versus peasant mothers [25]. Conversely, in an Ethiopian study the children of literate mothers had a reduced risk of stunting, yet there was no signiﬁcant difference in employment [24].

Non-widowed single motherhood was associated with a higher risk of stunting in Cameroon and the DRC [30]. When controlled for economic resources, parental resources and health behavior, there was, however, no significant difference. The same study found no significant difference between widowed and married women. Habaasaet al.found in 2015 no significant effect of mother's marital status [25]. A study in the DRC examined specifically the effect of women's decision-making power on their children's risk of stunting. In western provinces, the risk rose significantly if the mother did not

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take part in decisions regarding her husband's income. In all of the DRC, both a joint decision about the husband's income and the decision made by the husband alone were associated with a higher risk than if the mother made such a decision by herself.

3.4.5. Household wealth

Several studies consistently found that increased household wealth decreased the risk of stunting.

Children in households with a wealth status in the 5^thquintile had a much lower risk for stunting than the 1^stquintile (24). A rich household was associated with a lower risk of stunting in four out offive studies comparing household wealth [21,27,29,31]. Being part of a severely food insecure household, which could be viewed as another facet of household wealth, was also associated with a greater risk of stunting [23]. Likewise, children of families who were current food aid beneficiaries were at higher risk [26]. Furthermore, an increased GDP per capita reduced the risk of stunting among children underfive years [31]. Children in rural households were also found to be at greater risk as compared to urban households [21,29,31].

4. Discussion

We found a high prevalence of stunting in under-five children in SSA. According to Berendsenet al., 41.1% were stunted in 2016 [20]. Most of the studies included were conducted in recent years or in small districts, making the estimation of any time-trend difficult. Comparison with other studies may, however, offer some insight. A 2008 study found a prevalence of 37.7% in Western Africa, 41.5% in Central Africa, 50.0% in Eastern Africa and 30.2% in Southern Africa [2]. This is consistent with our results showing that Central and Eastern Africa were the most affected. Ourfindings were also supported by a 2020 report, although showing a few percentage points lower prevalence in all regions but Southern Africa [33]. Western and Southern Africa fell in the category of having a high prevalence, i.e.

20 -<30%, whereas Central and Eastern Africa had a very high prevalence, i.e.30% [5,34].

In two Ugandan districts, almost 40% of the under-ﬁve children were stunted, but newer data from 2016 showed a prevalence just below 30% [21,22]. The national DHS included more participants and may be more representative of all regions. Another 2016 study conducted in South-Western Uganda found a prevalence of 25% [35]. Thus, the prevalence seems to have been reduced.

The prevalence of stunting in Ethiopia was approximately 20%. Forty percent of the children did not have an adequately diverse diet. This is possibly a result of the common belief that young children are not able to chew and digest meat and some dairy products and hence are not given these, thus missing out on important protein and micronutrient sources [23]. A 2011 DHS from Ethiopia showed that the prevalence of stunting was as high as 44% [6]. Since joining the Scaling Up Nutrition Movement however, Ethiopia has experienced a twenty percent drop in malnutrition, which is reﬂected in the 2016 DHS showing a stunting prevalence of 27% [22,36].

Altogether, viewing the prevalence of stunting in percentages, the trend was a reduction. The joint child malnutrition estimates in fact reported a reduction in child stunting in SSA from 43.1% to 32.7%

between 2000 and 2019 [33]. This represents a reduction of approximately 25%. Although the trend in the prevalence of child stunting is pointing downwards, the rate is too slow to reach the global nutrition target of a 40% reduction within 2025. Reaching the target is unrealistic, especially bearing in mind that these data do not cover the covid-19 pandemic. Action is needed to reduce stunting in SSA.

To create impactful policies, knowing the determinants of child stunting is essential.

This study identified several risk factors of stunting. Significant predictors were the child's age, gender, and birth weight, the interpregnancy interval, the number of children underfive years in the same household, the mother's education level as well as household wealth status. This is supported by a 2020 scoping review on risk factors associated with stunting and other malnutrition conditions in under-five children in SSA [37].

Male children were at higher risk of stunting than female children. This is consistent with a meta- analysis on 16 demographic and health surveys in 10 countries in SSA [38]. One reason could be biological, with boys having a higher energy requirement than girls [39]. There is also some evidence suggesting that male children are more prone to infections than their female counterparts [38].

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Infection may lead to a lower food intake which in turn increases the infection risk and this could become a vicious cycle [40].

Infants were found to be at lower risk than children. A 2017 review supports this result [41]. One explanatory factor could be breastfeeding in theﬁrst months of life. Breastmilk is optimized to meet the infant's needs through its composition of amino acids, fatty acids, vitamins, immune factors, and its energy content [39]. When breastfeeding is discontinued and/or complementary foods are introduced, an infant may receive a less energy and nutrient dense diet. This may compromise their growth and development. Furthermore, without breastmilk and its immune factors, the infant is no longer offered the same protection against infections [39]. After exclusive breastfeeding, it is important to offer the child nutritious meals multiple times a day due to their small stomach. Knowledge about feeding practices varies among parents. Moreover, some women are required to return to work early to support their familiesﬁnancially, and hence the child is left in another family member or an older child's care. A lack of such knowledge among parents or caretakers could thus contribute to the higher risk in children.

The timing of the BCG, DTP1 and MV vaccines decreased the risk of stunting if given early and increased the risk if given late. This might be due to the anti-inflammatory profile of the neonatal immune system that changes towards a pro-inflammatory profile as the infant grows into a child.

Confounding variables could have inﬂuenced the result, as children who are early vaccinated also had higher educated mothers and received more healthcare overall [20]. While such vaccines will reduce important infections that can hamper child linear growth, enteric dysfunction increases the risk of child stunting [42], and the gut microbiota has emerged as a factor that can affect stunting, but data are inconsistent. For example, studies have demonstrated a causative role of an altered gut microbiota in undernourished children, and correction to an adequate gut microbiota may promote healthy growth [43]. However, in a randomized nutritional intervention trial in rural Uganda we did notﬁnd any association between gut microbiota-composition and child stunting [44]. Similarly, in their hospital- based randomized trial examining the effect of co-trimoxazole prophylaxis, Berkleyet al.found no statistical difference in Kenyan child anthropometry between the intervention and control group [45].

Households with several children underﬁve living together increased the risk of stunting in those children. That is reasonable because the food available must be distributed between family members, which particularly increases the risk of undernutrition in less resourceful households. Having twins or more also increased risk, as it naturally puts an additional pressure on the caretakers and the household resources as compared to a singleton. Short interpregnancy intervals contribute to having more children underﬁve in the same household and was also independently associated with a higher risk of stunting. If the mother is nutritionally depleted after a pregnancy, a short birth interval would impede the restoration of her nutritional status. That could compromise the nutrient need of the growing fetus, increasing the risk of low birth weight and thus the risk of the child becoming stunted [46]. Of interest, a Zambian study showed that maternal height predicts the height of their offspring [47]. One study found that maternal nutrition and infection accounted for 12.2% of stunting cases among two year old children in SSA in 2011 [11]. In the same study, teenage motherhood and short birth intervals accounted for only 2%, whereas fetal growth restriction and preterm birth were associated with the largest burden of stunting, explaining 30.6% of the cases. Besides, short interpregnancy intervals could be associated with less family planning abilities or the mother having less decision- making power. Both could be indications of fewer resources being available and lower household wealth, thereby offering another explanation of the increased stunting risk.

Maternal education level played a significant role in stunting risk in SSA. Strengthening thisfinding, a scoping review found maternal education to be the strongest predictor of stunting in most studies covering parental factors [37]. One possible explanation could be that higher education requires literacy, and literacy enables the mother to receive more health information. Maternal literacy and education has been associated with better feeding practices and nutrition status in Ugandan children [48]. Naet al.found that empowered women, especially economically empowered women, were more likely to fulfill recommended infant and young child feeding practices [49]. Berhaneet al.found that higher educated mothers gave their children a more diversified diet [23]. Moreover, higher education gives access to a higher income, increasing household wealth.

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Adding to the issue of maternal impact on their children's linear growth, are transgenerational effects mediated by epigenetic programming [50]. Although still in its infancy, research on epigenetic mechanisms regulating growth may reveal important avenues for optimizing child growth [51].

Household wealth was signiﬁcantly associated with stunting in several studies. A 2020 review on Ethiopian children found that low economic class may predispose childhood stunting [52]. One possible explanation is that higher household wealth can increase access to healthcare for both mother and child. This may positively inﬂuence the mother's nutrition status and overall health status, enabling a safer and more growth promoting pregnancy. Healthcare facilities may provide breastfeeding encouragement and support, monitor the child's growth, and give treatment for infections.

Another explanation lies in the access to proper sanitation, because being able to wash one's hands, drink clean water and prepare food in a clean environment protects against infection. A Ugandan study found that the main predictors of child stunting were household sanitation, poverty, and low dietary diversity [35].

Closely related to household wealth, food security was a signiﬁcant predictor of child stunting. Food secure households have been found to provide their children a diet twice as diversiﬁed as food insecure households [23]. The 2020 FAO report on the state of food security and nutrition in the world con- textualizes the issue of food insecurity. In 2019, 227.5 million people were severely food insecure in SSA. Food security consists of availability, access, utilization, and stability. The cost of a nutrient adequate and a healthy diet lies 1.7 and 3.2 times above the poverty line in SSA, respectively. Although a nutrient adequate diet represents less than the average daily food expenditures per capita (91%), the affordability varies across regions. In Eastern, Middle and Western Africa, a healthy diet is not affordable. In fact, 53% cannot afford a nutrient adequate diet in SSA. Furthermore, access to refrig- eration and other food conservation varies among households and communities. Thus, the impact of household wealth on stunting was unsurprising [5].

Climate change is another environmental factor that threatens food security and thus could increase child stunting [16,53]. The Convention on the Rights of the Child clearly states that the impact of environmental pollution must be considered when securing the child's right to adequate nutrition [9].

Extreme weather, drought, and loss of biodiversity are some examples of events that increase in fre- quency and severity through climate change. It is estimated that climate change could cause the consumer price of maize and other coarse grains to rise by 150e200 percent between 2010 and 2030, putting more households into poverty and increasing the number of stunted children [5]. Households that are already poor and vulnerable to extreme weather will become even less resilient in the future.

Consequently, disparities in socioeconomic status and health will be exacerbated. A 2016 study found that 27% of stunting cases among two year old children in SSA were attributable to environmental factors [11]. This is likely to increase over the next years. The impact of climate change must be accounted for when making policies [54].

Maternal education, child feeding practices and environmental factors are the most important targets for interventions to prevent child stunting. Maternal education was strongly associated with stunting in several of the studies. Through education, women gain access to a higher wage, also increasing empowerment, household wealth and health seeking behaviors [55]. Furthermore, higher paying jobs as compared to for instance cultivating ﬁelds are often less physically demanding, increasing the likelihood of better maternal nutrition status, and making breastfeeding more available.

Child feeding practices vary greatly between communities. False beliefs about digestion abilities or the child's small size being normal, and prioritization of male family members put women and children in disadvantageous positions. In addition, knowledge about the beneﬁts of breastfeeding is key to ensuring proper nutrition in theﬁrst months of life. Targeting these practices enables families to provide diverse and nutritious foods for their children and to make more health-promoting prioriti- zations when necessary [56]. Climate change is an external factor that threatens food security, exac- erbating any negative effect of poor household wealth or improper feeding practices. The consequences of doing nothing are great and increase over time [16]. Hence, policies made locally, nationally, and globallyeincluding in industrialized countries that pollute and exploit the resources of developing countrieseshould target these three determinants.

The strengths of this study include that most of the countries in SSA are represented, including the most populated countries. Most studies included were based on national DHSs. These are routinely

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conducted, meaning that recent data was available for most countries. The surveys were standardized, and conducted by trained staff, enabling comparison of the results. In addition, most surveys included several items on risk factors, strengthening the data basis. Furthermore, including both small- and large-scale studies uncovered more details about the determinants of child stunting, including local infant and young child feeding practices.

This study had several limitations. All studies included were cross-sectional and can therefore highlight associations, but not prove causality. Most studies were based on DHSs, which give a large population number, however they may not be representative because there is a lack of birth regis- trations in SSA. The incomplete registration could lead to wrong age data or children not being included in studies. The result is most likely an underestimation of undernutrition [57,58]. Furthermore, household wealth in DHSs is measured through an approximation based on assets, not household income and -expenditure. This may also lead to an underestimation, as assets could have been bought in times of economic well-being or be inherited, but not necessarily contribute to food access in the present moment or in recent years. Moreover, we did not have speciﬁc criteria according to whether a possible confounding factor could be present, and we did not include the STROBE grading for quality of the studies.

In conclusion, the prevalence of stunting in children underﬁve years of age in Sub-Saharan Africa has been reduced over the last two decades and currently lies at approximately forty percent. However, the reduction rate has been slow, and if kept the same, we will not reach the WHO global nutrition target of a 40% reduction within 2025. Child stunting is caused by a complex set of factors relating to the mother's nutritional status, health and education, interpregnancy interval, the child's birth weight, vaccinations and infections, infant and young child feeding practices, household wealth, food security and other environmental factors. Policies and interventions should target education for women, child feeding practices and environmental factors including climate change, as these are the strongest determinants.

Funding

POI received funding from the Throne Holst Foundation and the Centre for Global Health at the University of Oslo's Research ExceLlence and Innovation in Global HealTh (RELIGHT) programme.

Declaration of competing interest

The authors declare no potential conﬂicts of interest.

Acknowledgments

We thank Dr. Ane Westerberg for critically reviewing the manuscript.

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