Leisure time, occupational, and commuting physical activity and the risk of stroke

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Activity and the Risk of Stroke

Gang Hu, PhD; Cinzia Sarti, PhD; Pekka Jousilahti, PhD; Karri Silventoinen, PhD;

Noe¨l C. Barengo, MD; Jaakko Tuomilehto, PhD

Background and Purpose—The role of physical activity, especially that of occupational and commuting physical activity, in the prediction of stroke risk is not properly established. We assessed the relationship of different types of physical activity with total and type-specific stroke risk.

Methods—We prospectively followed 47 721 Finnish subjects 25 to 64 years of age without a history of coronary heart disease, stroke, or cancer at baseline. Hazard ratios (HRs) for incident stroke were estimated for different levels of leisure time, occupational, and commuting physical activity.

Results—During a mean follow-up of 19.0 years, 2863 incident stroke events were ascertained. The multivariate-adjusted (age, sex, area, study year, body mass index, systolic blood pressure, cholesterol, education, smoking, alcohol consumption, diabetes, and other 2 types of physical activity) HRs associated with low, moderate, and high leisure time physical activity were 1.00, 0.86, and 0.74 (Ptrend⬍0.001) for total stroke, 1.00, 0.87, and 0.46 (Ptrend⫽0.011) for subarachnoid hemorrhage, 1.00, 0.77, and 0.63 (Ptrend⫽0.024) for intracerebral hemorrhage, and 1.00, 0.87, and 0.80 (Ptrend⫽0.001) for ischemic stroke, respectively. The multivariate-adjusted HRs associated with none, 1 to 29, andⱖ30 minutes of active commuting were 1.00, 0.92, and 0.89 (Ptrend⫽0.043) for total stroke, and 1.00, 0.93, and 0.86 (Ptrend⫽0.028) for ischemic stroke, respectively.

Occupational activity had a modest association with ischemic stroke in the multivariate analysis (Ptrend⫽0.046).

Conclusion—A high level of leisure time physical activity reduces the risk of all subtypes of stroke. Daily active commuting also reduces the risk of ischemic stroke.(Stroke. 2005;36:000-000.)

Key Words:incidence 䡲 exercise 䡲 stroke

T

here is good evidence that regular physical activity reduces the risk for cardiovascular disease.¹ However, the protective effect of physical activity on stroke risk is less clear, and the results are inconsistent. Several studies have found an inverse association between regular physical activity and the risk of stroke,^2–7whereas others have indicated a U-shaped association or no association.^{8 –12}In addition, it is not clear whether other types of physical activities, such as occupational and daily commuting physical activity on foot or by bicycle, are independently related to the risk of stroke.

These studies have focused on total stroke risk, and few studies have assessed the association between physical activity and different subtypes of stroke.^3,7,11A recent meta-analysis comprising 23 studies indicated that a high level of physical activity is associated with a reduced risk of total, ischemic, and hemorrhagic strokes.¹³The aim of this study is to assess whether leisure time, occupational, or commuting physical activity is independently associated with a reduced risk of total and different types of stroke.

Methods

Subjects

Between 1972 and 1997, every 5 years, 6 independent population surveys were performed in 5 geographic areas of Finland among the population 25 to 64 years of age. The sampling methods have been described previously in detail.¹⁴ The total sample size of the 6 surveys was 52 058. The participation rate varied by year from 74%

to 88%.¹⁴After excluding 2002 subjects with a history of coronary heart disease, stroke, or cancer at baseline, and 2335 with incomplete data on any required variables, the present analyses include 22 841 men and 24 880 women. These surveys were conducted according to the ethical rules of the National Public Health Institute, and the investiga- tions were performed in accordance with the Declaration of Helsinki.

Baseline Measurements

A self-administered questionnaire was mailed to participants including questions about smoking, alcohol consumption, socioeconomic factors, medical history, and physical activity: leisure time, occupational, and commuting physical activity. Details have been presented previously,^15–22and these questions were similar to those used and validated in the Seven Countries Study.²³ In addition, physical activity has been successfully used previously, showing a high

Received February 9, 2005; final revision received June 2, 2005; accepted June 19, 2005.

From the Department of Epidemiology and Health Promotion, National Public Health Institute, Helsinki, Finland (G.H., C.S., P.J., J.T.); Department of Public Health, University of Helsinki, Finland (G.H., C.S., P.J., K.S., J.T.); Department of Public Health and General Practice, University of Kuopio, Finland (N.C.B.); and South Ostrobothnia Central Hospital, Seina¨joki, Finland (J.T.).

Correspondence to Gang Hu, MD, PhD, Department of Epidemiology and Health Promotion, National Public Health Institute, Mannerheimintie 166, FIN-00300 Helsinki, Finland. E-mail hu.gang@ktl.fi

Strokeis available at http://www.strokeaha.org DOI: 10.1161/01.STR.0000177868.89946.0c

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by guest on April 20, 2018http://stroke.ahajournals.org/Downloaded from

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correlation with physical fitness, as measured by maximal oxygen uptake.²⁴Self-reported leisure time physical activity was classified into 3 categories: (1) low (almost completely inactive, eg, reading, watching television, or doing some minor physical activity that was not of a moderate or high level), (2) moderate (some physical activity for⬎4 hours per week, eg, walking, cycling, light gardening, but excluding travel to work), and (3) high (vigorous physical activity for⬎3 hours per week, eg, running, jogging, swimming, heavy gardening, or regular exercise or competitive sports several times per week). Occupational physical activity was classified as: (1) light (physically very easy, sitting office work, eg, secretary), (2) moderate (standing and walking, eg, store assistant, light industrial worker), and (3) active (walking and lifting, or heavy manual labor, eg, industrial or farm work). The daily commuting return journey was categorized into 3 categories: (1) using motorized transportation or no work (0 minutes of walking or cycling), (2) walking or bicycling 1 to 29 minutes, and (3) walking or bicycling forⱖ30 minutes. Measurements of height, weight, systolic blood pressure (SBP), and serum total cholesterol were made at baseline examination using a standardized protocol.¹⁴

Prospective Follow-Up

The study cohorts were followed until the end of 2003 through computer- ized register linkage by identification numbers. Mortality data were obtained from Statistics Finland and data on nonfatal events from the National Hospital Discharge Register. The Eighth, Ninth, and Tenth Revisions of the International Classification of Diseases(ICD) were used to identify subarachnoid hemorrhage (430 and I60), intracerebral hemorrhage (431 and I61–I62), intracerebral infarction (432 to 438 and I63–I66), and any stroke (430 to 438 and I60–I66) events. ICD-9 code 432 was classified as an intracerebral hemorrhage. Stroke events that occurred before the baseline survey were identified from the Hospital Discharge Register and excluded from the analyses. The validity of the diagnosis of acute stroke in Finland is good for hospital discharge register (agreement in 90%) and death register (agreement in 97%).²⁵End points during follow-up were incident stroke events, defined as either the first nonfatal stroke event or stroke death without a preceding nonfatal event. Altogether, we identified cerebrovas- cular 2863 events (260 subarachnoid hemorrhage, 339 intracerebral hemorrhage, and 2264 ischemic) during a mean follow-up of 19.0 years.

Statistical Analyses

Independent samplesttests and␹²tests were used to compare the mean levels of continuous variables and the prevalence of categorical variables between subjects with and without incident stroke. We assessed correlations of any 2 types of physical activity through partial correlation coefficients and estimated the association of physical activity with stroke risk by Cox proportional hazard models. Physical activity categories were included in the models as dummy and categorical variables, and the significance of the trend over different categories of physical activity was tested in the same models by giving an ordinal numeric value for each dummy variable. The proportional hazards assumption in the Cox model was assessed with graphical methods and with models including time-by-covariate interactions (time-dependent, all types of physical activity).²⁶In general, all proportionality assump- tions were appropriate across different types of stroke with different types of physical activity. The analyses were first performed adjusting for age, area, and study year, and further for education (tertiles), body mass index (BMI), SBP, total cholesterol, smoking (never, past, and current), alcohol consumption (yes/no), history of diabetes (yes/no), and the other 2 types of physical activity. Because the interactions between sex and each type of physical activity on stroke risk were not statistically significant, data for men and women were combined in some analyses.

Results

General characteristics of the study population at baseline are presented in Table 1. Age-, sex-, area-, and study year–

adjusted correlations were 0.19 for occupational and commuting physical activity (P⬍0.001),⫺0.03 for occupational and leisure time physical activity (P⬍0.001), and 0.07 for commuting and leisure time physical activity (P⬍0.001).

Leisure Time Physical Activity and the Risk of Stroke Age-, area-, and study year–adjusted hazard ratios (HRs) of stroke incidence associated with low, moderate, and high leisure time physical activity were 1.00, 0.80, and 0.59 (P_trend⬍0.001) in men, 1.00, 0.82, and 0.67 (P_trend⬍0.001) in women, and 1.00, 0.81, and 0.62 (Ptrend⬍0.001) in men and women combined (adjusted also for sex), respectively (Table 2). Further adjustment for other risk factors (education, BMI, SBP, cholesterol, smoking, alcohol consumption, and diabetes) and even for occupational and commuting physical activity affected the results only slightly (allP_trend⬍0.05).

Occupational Activity and the Risk of Stroke There was a nonsignificant inverse association between occupational activity and the stroke risk in men and women. In both sexes combined, the inverse association was significant after adjustment for age, sex, area, study year, and other risk factors (the HRs associated with light, moderate, and active occupational activity were 1.00, 0.90, and 0.87, respectively;

Ptrend⫽0.007) but no longer after additional adjustment for leisure time and commuting physical activity (P_trend⫽0.060).

When moderate and active occupational activity were combined, the HR at moderate/active occupational activity versus light occupational activity was 0.91 (95% CI, 0.84 to 0.99;

P⫽0.027) after adjustment for all confounding factors, including leisure time and commuting physical activity.

Commuting Physical Activity and the Risk of Stroke Daily commuting physical activity on foot or by bicycle was modestly and inversely associated with the risk of stroke among men (Ptrend⫽0.047) and women (Ptrend⫽0.018) after adjustment for age, area, study year, and other risk factors. In both sexes combined, the inverse association remained modest after adjustment for sex, other risk factors, leisure time, and occupational physical activity (the HRs associated with none, 1 to 29, andⱖ30 minutes of active commuting were 1.00, 0.92, and 0.89, respectively;Ptrend⫽0.043).

All Three Types of Physical Activity and the Risk of Stroke

In the multivariate analyses, we estimated joint effects of all 3 types of physical activity on stroke risk (Table 3). We dichotomized all 3 types of physical activity at low/light versus moderate to high/active levels for leisure time and occupational physical activity and for commuting physical activity (any versus none). Compared with the subjects who reported low levels of leisure time, occupational, and commuting physical activity, the participants who reported 2 or 3 types of moderate to high physical activity had a 21% to 31%

decreased risk of stroke, and the participants who reported only 1 of 3 types of moderate to high physical activity had a 14% to 21% decreased risk of stroke.

Physical Activity and the Risk of Stroke Subtypes After adjustment for age, sex, other risk factors, and occupational and commuting physical activity, the HRs associated with low, moderate, and high leisure time physical activity were 1.00, 0.87, and 0.46 (Ptrend⫽0.011) for subarachnoid hemorrhage, 1.00, 0.77, and 0.63 (P_trend⫽0.024) for intrace-

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rebral hemorrhage, and 1.00, 0.87, and 0.80 (Ptrend⫽0.001) for ischemic stroke, respectively (Table 4). Modest associations between occupational activity and ischemic stroke (Ptrend⫽0.046) and between commuting physical activity and ischemic stroke (Ptrend⫽0.028) were found in the multivariate analyses. When we used nonfatal stroke events as outcome, these inverse associations between leisure time physical activity and each type of subarachnoid hemorrhagic, intracerebral hemorrhagic, and ischemic stroke, modest associations between occupational activity and ischemic stroke, and between commuting physical activity and ischemic stroke did not appreciably change (data not shown).

Discussion

A high level of leisure time physical activity reduced the risk for total and different subtypes of stroke incidence, including subarachnoid hemorrhagic, intracerebral hemorrhagic, and ischemic strokes. Moderate level of leisure time physical activity reduced the risk for intracerebral hemorrhagic and ischemic strokes. Daily commuting physical activity on foot or by bicycle reduced the risk of ischemic stroke. A simultaneous engagement in 2 or 3 types of physical activity showed a slightly stronger protective effect than having only 1 type of activity.

The findings from the previous prospective studies on the association between leisure time physical activity and stroke risk are inconsistent. Some studies,^2–7 but not all,^{9 –12} have indicated a significant inverse association between leisure time physical activity and stroke risk. Moreover, studies on women are sparse,^{4 –7,12} and only 3 of them have found a significant inverse association between leisure time physical activity and stroke risk.^5–7 Small sample sizes and few stroke events, especially among women, may have contributed to the inconsistent observations. Our study with a large sample size and the largest number of stroke events during follow-up reported thus far provides strong evidence for the benefits of leisure time physical activity on the prevention of stroke in men and women.

The incidence rates of total stroke were 3.56 per 1000 person years in men and 2.81 per 1000 person years in women in this population, which is higher than other populations.^7,10

Only 2 studies have assessed the association between occupational activity and stroke risk, and no significant association was found.^8,12 We showed that active occupational activity was modestly associated with a lower risk of total stroke incidence when both sexes were combined but neither in men nor in women separately. This indicates that the magnitude of the effect is not very large (⬇10%) and thus requires a large sample size like in our study to be detected.

TABLE 1. General Characteristics of Study Subjects at Baseline According to the Stroke Outcome During the Follow-Up*

Men

PValue†

Women

PValue†

Nonstroke (n⫽21 344)

Stroke (n⫽1497)

Nonstroke (n⫽23 514)

Stroke (n⫽1366)

Age, y 42.8 49.5 ⬍0.001 43.5 52.0 ⬍0.001

BMI, kg/m² 26.1 26.9 ⬍0.001 25.9 28.0 ⬍0.001

SBP, mm Hg 142 152 ⬍0.001 138 155 ⬍0.001

Total cholesterol, mg/dL 237 257 ⬍0.001 232 262 ⬍0.001

Education, % 0.027 0.19

Tertile 1 25.7 26.7 30.3 29.1

Tertile 2 34.8 37.5 33.3 35.6

Tertile 3 39.5 35.8 36.4 35.3

Alcohol drinker, % 66.3 62.9 0.008 36.4 21.9 ⬍0.001

Current smoker, % 42.7 48.7 ⬍0.001 17.7 14.3 0.001

Diabetes, % 1.7 4.6 ⬍0.001 1.6 4.5 ⬍0.001

Leisure time physical activity, % ⬍0.001 ⬍0.001

Low 28.2 36.7 37.1 50.8

Moderate 51.4 52.5 49.4 42.2

High 20.4 10.8 13.5 7.0

Occupational activity, % 0.003 ⬍0.001

Light 34.0 36.0 40.8 44.8

Moderate 22.7 18.9 32.5 26.7

Active 43.3 45.1 26.7 28.5

Walking or cycling to/from work, % 0.001 ⬍0.001

0 min/day 50.0 51.4 42.9 54.8

1–29 min/day 32.8 28.6 33.7 25.1

ⱖ30 min/day 17.2 20.0 23.4 20.1

*Characteristics are defined at baseline examination (see Methods); †ttest for continuous variables and␹²test for categorical variables.

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TABLE 2. HRs of Total Stroke According to the Levels of Leisure-Time, Occupational, and Commuting Physical Activity

Cases, No. Person Years

HRs (95% CI)*

Model 1 Model 2 Model 3

Men

Leisure time physical activity

Low 550 121 111 1.00 1.00 1.00

Moderate 786 216 297 0.80 (0.72–0.89) 0.83 (0.75–0.93) 0.84 (0.75–0.94)

High 161 83 323 0.59 (0.50–0.71) 0.72 (0.60–0.86) 0.72 (0.60–0.87)

Pfor trend ⬍0.001 ⬍0.001 ⬍0.001

Occupational activity

Light 539 123 097 1.00 1.00 1.00

Moderate 283 99 895 0.84 (0.72–0.97) 0.89 (0.77–1.03) 0.93 (0.80–1.08)

Active 675 197 739 0.91 (0.81–1.02) 0.89 (0.79–1.00) 0.90 (0.80–1.03)

Pfor trend 0.050 0.12 0.30

Walking or cycling to/from work, min/day

0 770 194 766 1.00 1.00 1.00

1–29 428 144 765 0.86 (0.77–0.97) 0.91 (0.81–1.03) 0.94 (0.83–1.06)

ⱖ30 299 81 200 0.82 (0.71–0.93) 0.85 (0.74–0.97) 0.88 (0.77–1.02)

Pfor trend 0.004 0.047 0.22

Women

Low 696 197 076 1.00 1.00 1.00

Moderate 577 229 716 0.82 (0.73–0.91) 0.86 (0.77–0.97) 0.87 (0.78–0.98)

High 93 59 099 0.67 (0.54–0.83) 0.75 (0.61–0.94) 0.77 (0.62–0.97)

Pfor trend ⬍0.001 0.007 0.013

Light 612 179 762 1.00 1.00 1.00

Moderate 365 163 588 0.87 (0.76–0.99) 0.90 (0.79–1.03) 0.95 (0.83–1.09)

Active 389 142 541 0.88 (0.77–1.00) 0.86 (0.75–0.98) 0.89 (0.78–1.03)

Pfor trend 0.059 0.065 0.28

0 745 200 918 1.00 1.00 1.00

1–29 343 165 912 0.83 (0.73–0.94) 0.86 (0.75–0.98) 0.88 (0.77–1.01)

ⱖ30 278 119 061 0.80 (0.70–0.93) 0.85 (0.73–0.97) 0.87 (0.75–1.01)

Pfor trend 0.001 0.018 0.093

Men and women combined†

Low 1246 318 187 1.00 1.00 1.00

Moderate 1363 446 013 0.81 (0.75–0.87) 0.85 (0.79–0.92) 0.86 (0.79–0.93)

High 254 142 422 0.62 (0.54–0.72) 0.73 (0.64–0.84) 0.74 (0.64–0.85)

Pfor trend ⬍0.001 ⬍0.001 ⬍0.001

Light 1151 302 858 1.00 1.00 1.00

Moderate 648 263 484 0.85 (0.77–0.94) 0.90 (0.82–0.99) 0.94 (0.85–1.04)

Active 1064 340 280 0.90 (0.82–0.98) 0.87 (0.80–0.95) 0.89 (0.81–0.98)

Pfor trend 0.003 0.007 0.060

0 1515 395 684 1.00 1.00 1.00

1–29 771 310 677 0.84 (0.77–0.92) 0.89 (0.82–0.98) 0.92 (0.84–1.01)

ⱖ30 577 200 261 0.81 (0.73–0.89) 0.85 (0.78–0.94) 0.89 (0.80–0.98)

Pfor trend ⬍0.001 0.002 0.043

*Model 1, Adjusted for age, area, and study year; model 2, additionally adjusted for BMI, SBP, cholesterol, education, smoking, alcohol consumption, and diabetes; model 3, models 2 and also adjusted for other 2 types of physical activity. †Also adjusted for sex.

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Occupational physical activity also modestly reduced the risk of ischemic stroke when both sexes were combined.

We found that daily commuting activity on foot or by bicycle may reduce total stroke risk. This is an important finding because daily active commuting is a major source of total physical activity in some populations, it can be imple- mented virtually everywhere, and is inexpensive. For in- stance, in urban China, ⬎90% of people walk or cycle to work daily.²⁷ In our study, ⬎40% of the Finnish subjects reported walking or cycling to work daily. Several studies have shown that regular active commuting is related to lower levels of cardiovascular risk factors^15,28and reduces mortality among diabetic patients.¹⁸

Few studies have examined the association between physical activity and the risk of different subtypes of stroke, and the results are inconsistent.^3,7,11In the Honolulu Study,³active men experienced a lower risk of subarachnoid hemorrhagic or intracerebral hemorrhagic stroke compared with inactive men, but no significant association of physical activity on thromboembolic stroke risk was found. In the Physicians’ Health Study,¹¹ an inverse association of leisure time physical activity on hemor-

rhagic stroke risk disappeared after adjustment for other confounding factors, and no significant association with ischemic stroke was present. In the Nurses’ Health Study,⁷regular leisure time physical activity was associated with a reduced risk of ischemic stroke only but not with subarachnoid hemorrhagic or intracerebral hemorrhagic stroke. These studies usually have a relatively small number of hemorrhagic stroke cases. The present study is, to our knowledge, the first that has found an inverse association of leisure time physical activity on the risk of each type of subarachnoid hemorrhage, intracerebral hemorrhage, and ischemic stroke. A recent meta-analysis comprising 6 ischemic and 3 hemorrhagic stroke studies indicated that highly active individuals had a reduced risk of ischemic and hemorrhagic strokes than low-active individuals,¹³in keeping with our results. However, it did not separately analyze subarachnoid hemorrhagic stroke and intracerebral hemorrhagic stroke.¹³In- terestingly, only leisure time physical activity protected from subarachnoid hemorrhagic. Occupational activity often includes isotonic bouts of activity that are known to trigger the rupture of aneurysms and the onset of subarachnoid hemorrhagic stroke.

TABLE 3. HRs of Total Stroke According to Combined Levels of Leisure Time, Occupational, and Commuting Physical Activity*

HRs (95% CI)

Low Leisure-Time Physical Activity Moderate or High Leisure-Time Physical Activity

No Active Commuting

Walking or Cycling to/from

Work⬎1 min/day No Active Commuting

Walking or Cycling to/from Work⬎1 min/day

Light occupational activity 1.00 0.79 (0.63–0.98) 0.81 (0.71–0.93) 0.69 (0.57–0.82)

Moderate or active occupational activity 0.86 (0.74–1.00) 0.79 (0.69–0.90) 0.69 (0.60–0.81) 0.69 (0.61–0.79)

*Adjusted for age, sex, area, study year, BMI, SBP, cholesterol, education, smoking, alcohol consumption, and diabetes.

TABLE 4. HRs of Different Subtypes of Stroke According to the Level of Leisure Time, Occupational, and Commuting Physical Activity*

Subarachnoid Hemorrhagic Stroke Intracerebral Hemorrhagic Stroke Ischemic Stroke Cases,

No.

Person y

HRs

(95% CI) Cases, No.

Person y

HRs (95% CI)

Cases, No.

Person y

HRs (95% CI) Leisure time physical

activity

Low 110 324 241 1.00 151 324 419 1.00 985 319 003 1.00

Moderate 132 452 864 0.87 (0.67–1.13) 158 453 088 0.77 (0.61–0.97) 1073 447 135 0.87 (0.79–0.95)

High 18 143 775 0.46 (0.27–0.76) 30 143 766 0.63 (0.42–0.95) 206 142 492 0.80 (0.68–0.93)

Pfor trend 0.011 0.024 0.001

Light 81 308 150 1.00 130 308 242 1.00 940 303 376 1.00

Moderate 77 266 857 1.22 (0.88–1.69) 84 267 072 1.05 (0.78–1.40) 487 264 135 0.90 (0.80–1.01)

Active 102 345 873 1.06 (0.77–1.46) 125 345 959 0.91 (0.69–1.20) 837 341 119 0.88 (0.80–0.98)

Pfor trend 0.48 0.63 0.046

0 115 403 050 1.00 174 403 276 1.00 1226 396 592 1.00

1–29 78 314 770 0.93 (0.69–1.26) 93 314 754 0.93 (0.71–1.21) 600 311 187 0.93 (0.84–1.03)

ⱖ30 67 203 060 1.17 (0.85–1.60) 72 203 243 0.96 (0.72–1.28) 438 200 851 0.86 (0.76–0.96)

Pfor trend 0.39 0.85 0.028

*Adjusted for age, sex, area, study year, BMI, SBP, cholesterol, education, smoking, alcohol consumption, diabetes, and other 2 types of physical activity.

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The protective effect of physical activity may partly mediate through its effect on other risk factors of stroke.²⁹ Physical activity has a favorable effect on blood pressure, lipid profile, insulin sensitivity, body weight, blood coagulation, and fibrino- lysis10,15,17,28,30,31and also reduces the risk of hypertension and diabetes.^15,17,19 In our study, the inverse associations between physical activity and stroke risk remained significant also after controlling for the major cardiovascular risk factors.

There are several strengths and limitations in our study. Our study is population based, comprising a large number of men and women from a homogeneous population. The mean follow- up, 19.0 years, was long enough that the largest number of stroke events were ascertained without loss of follow-up. Not only leisure time physical activity but also occupational and commuting physical activities were included in the analysis.

Moreover, the subtypes of stroke were also analyzed. A limitation of our study was the self-report of physical activity.

Using a questionnaire to assess habitual physical activity is always crude and imprecise. We do not have data on possible changes in physical activity during follow-up. Misclassifica- tion, particularly over-reporting the amount of physical activity at baseline and changes in the activity during follow-up, probably lead to an underestimation of the association between physical activity and the outcome. We cannot completely exclude either the effects of residual confounding attributable to the measurement error in the assessment of confounding factors or some unmeasured dietary factors.

In conclusion, our study demonstrates that a higher level of leisure time physical activity reduces total and different subtypes of stroke risk. Commuting physical activity is inversely associated with ischemic stroke but not for subarachnoid and intracerebral hemorrhagic strokes.

Acknowledgments

This study was supported by grants from the Finnish Academy (46558, 204274, and 205657), the Ministry of Education, and the Finnish Foundation for Cardiovascular Research.

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