Abstract
Evaluation of: Sattelmair JR, Kurth T, Buring JE, Lee IM. Physical activity and risk of stroke in women. Stroke 41(6), 1243–1250 (2010).
Several meta-analyses support the importance of participation in regular, leisure-time physical activity for the primary prevention of stroke and cardiovascular disease, as well as other associated health benefits. Whether both men and women benefit is not clear, in part owing to there being relatively fewer women in relevant observational and case–control studies. Data from the Women’s Health Study have now been used to address this question in a large cohort of women. After multivariable adjustment, increasing levels of leisure-time physical activity in women tended to be associated with lower stroke risk, with a particular benefit of regular, brisk walking for those who did not vigorously exercise. The results reinforce recommendations that both men and women participate in regular, leisure-time physical activity.
Methods & results
The Women’s Health Study (WHS) was a randomized trial of low-dose aspirin and vitamin E for primary prevention of cardiovascular disease and cancer Citation[1]. The study included 39,876 initially healthy women aged greater than 45 years followed for 10-years, with a primary outcome of nonfatal myocardial infarction, nonfatal stroke and cardiovascular death. Aspirin 100 mg on alternate days had no effect on the overall primary outcome (2.4% with aspirin vs 2.6% with placebo, relative risk [RR] 0.91; 95% CI: 0.80–1.03; p = 0.13), but a 17% reduction in the risk of stroke (1.1% with aspirin vs 1.3% with placebo; RR: 0.83; 95% CI: 0.69–0.99; p = 0.04).
Data from the WHS were used for a secondary analysis of the impact of exercise on the risk of a first stroke Citation[2]. Unlike other observational studies that generally record the level of exercise based on a single baseline assessment, women participating in the WHS also completed questionnaires providing information about their physical activity after 36, 72, 96, 125 and 149 months. As would be expected, women who exercised more at baseline were generally healthier than those who did not participate in regular, leisure-time physical activity. A total of 579 strokes occurred over 11.9 years of follow-up. After multivariable adjustment, increasing levels of leisure-time physical activity tended to be associated with lower stroke risk (p for trend = 0.06), with the effect attenuated after further adjustment for other conditions (BMI, history of diabetes, history of elevated cholesterol and history of hypertension; p for trend = 0.21). For women who did not exercise vigorously, both increasing amount of leisure-time walking (p for trend = 0.002) and walking pace (p for trend = 0.007) were associated with lower stroke risk. Women who walked more than 2 h per week had a 30% lower risk of stroke (adjusted RR: 0.70; 95% CI: 0.52–0.94; p = 0.002). As in other studies using similar designs, the data may be affected by recall bias, and there could be unmeasured factors that could confound the analyses. Too few women changed their level of activity to assess its impact on stroke risk.
Discussion
Lifestyle factors, such as diet, moderation of alcohol consumption, abstinence from cigarette smoking and avoidance of second-hand tobacco smoke, and regular exercise, are recommended as means of preventing a first stroke Citation[3]. These recommendations are primarily based on observational studies, as randomized trials – except for certain lifestyle interventions, such as diet – are ethically or logistically unfeasible.
Based on a systematic literature review, a 1995 US National Institutes of Health Consensus Panel recommended, “regular physical activity at a level appropriate to physical capacity, needs, and interest for children and adults with a goal of at least 30 minutes of moderate-intensity physical activity on most, and preferably, all days of the week” Citation[4]. Reinforcing the importance of early exercise, a subsequent case–control study assessed the impact of participation in vigorous sports or other physical activities between the ages of 15 and 25 years on later stroke risk Citation[5]. Those who did not exercise had a threefold increased chance of stroke in later life (odds ratio [OR]: 3.0; 95% CI: 1.8–5.5), with a population attributable risk of 0.33 (95% CI: 0.16–0.46).
A systematic review identified 23 studies (18 cohort and five case–control) meeting inclusion criteria listed in MEDLINE between 1966 and 2002 Citation[6]. Combining both types of studies, highly active individuals had a 27% lower risk of stroke or death as compared with persons with lower levels of activity (RR: 0.73; 95% CI: 0.67–0.79), with a similar benefit in those engaging in moderate activity (RR: 0.80; 95% CI: 0.74–0.86). The effects were similar for reductions in ischemic and hemorrhagic stroke, with no statistical heterogeneity among studies overall or based on study type. Although studies including women were included, the data for men and women were not analyzed separately, and the types of activities were not addressed.
A second systematic review identified 31 relevant cohort (n = 24) or case–control (n = 7) studies listed in PUBMED up to December 2001 Citation[7]. As compared with those who were inactive, there were meaningful reductions in stroke risk for both those who engaged in high (RR: 0.78; 95% CI: 0.71–0.85) and moderate (RR: 0.85; 95% CI: 0.78–0.93) levels of activity, with no difference between the two activity levels (RR: 0.95; 95% CI: 0.68–1.32). There was no overall statistical heterogeneity among studies, although there was a greater benefit in studies conducted in Europe (RR: 0.47; 95% CI: 0.33–0.66) as compared with the USA (RR: 0.82; 95% CI: 0.75–0.90). Again, the results for men and women and the types of activities were not analyzed. The results of the two meta-analyses, however, were substantially similar.
Data from studies specifically addressing the potential effects of leisure-time physical activity on stroke risk in women as compared with men are limited. In contrast to the benefits suggested by the meta-analyses, the Atherosclerosis Risk in Communities Study found no overall relationship between leisure-time physical activity and stroke risk in men or women Citation[8]. By contrast, there was a reduction in stroke risk associated with physical activity in the Framingham cohort, but the effect was limited to men Citation[9]. Similarly, the beneficial effect of physical activity on stroke risk was restricted to men in the Northern Manhattan Stroke Study (NOMASS) cohort Citation[10]. Moderate- to heavy-intensity physical activity was associated with a 35% lower risk of ischemic stroke (hazard ratio [HR]: 0.65; 95% CI: 0.44–0.98), an effect present in men (HR 0.37; 95% CI: 0.18–0.78), but not women (HR: .92; 95% CI: 0.57–1.50). The 95% confidence intervals for men and women overlap, and the lack of statistical benefit in women might have been due to a type II error related to low power, or other unique features of the cohort.
Data showing a specific reduction in stroke associated with physical activity in women have been lacking. Although the overall benefit is of marginal statistical significance, the results of the WHS analysis Citation[2] are generally consistent with prior observational studies and meta-analyses, extending these results by supporting the benefit of leisure-time physical activity in reducing the risk of stroke in women. There is a particular benefit of brisk walking for those women not engaging in vigorous physical activity.
The effect of exercise on stroke risk might be mediated directly or indirectly through effects on other vascular risk factors such as obesity/overweight, diabetes/glucose intolerance and hypertension. Regardless of mechanism, the WHS findings reinforce those of the 2008 Physical Activity Guidelines Advisory Committee indicating that, “the least active people generally have the highest risk of a variety of negative health outcomes” and that, “although the minimum amount of activity needed to produce a benefit cannot be stated with certainty, nothing would suggest a threshold below which there are no benefits” Citation[11].
Engaging in regular, leisure-time physical activity is associated with a variety of health benefits, with the weight of the evidence reflecting a reduction in stroke risk. Further observational data is likely to be forthcoming over the next 5 years, but are unlikely to change this overall conclusion. Both men and women should be advised accordingly by their healthcare providers as part of a general strategy to lower their risk of a first stroke.
Key issues
• Engaging in regular, leisure-time physical activity is associated with a variety of health benefits, with the weight of the evidence reflecting a specific reduction in stroke risk.
• Data showing a specific benefit of leisure-time physical activity in women have been lacking.
• Data from the Women’s Health Study were used for a secondary analysis of the impact of exercise on the risk of a first stroke.
• After multivariable adjustment, increasing levels of leisure-time physical activity tended to be associated with lower stroke risk (p for trend = 0.06), with the effect attenuated after further adjustment for other conditions.
• Increasing amounts of leisure-time walking (p for trend = 0.002) and walking pace (p for trend = 0.007) were associated with lower stroke risk in women who do not vigorously exercise.
• Both men and women should be advised accordingly by their healthcare providers as part of a general strategy to lower their risk of stroke.
Financial & competing interests disclosure
The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.
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