Mark R. Etherton, MD, PhD
In this entry, I discuss a recent publication by Joshua Willey and colleagues regarding the protective effects of physical activity on stroke risk.
A beneficial role of physical activity in the prevention of cardiovascular disease and ischemic stroke has been consistently demonstrated. An outstanding question, however, is how changes in physical activity impact incident stroke risk. The authors of this manuscript, therefore, set out to investigate the association between changes in self-reported physical activity at two time points and incident stroke risk.
The authors used the California Teachers Study cohort, which is a large prospective cohort of female teachers in the state of California, and examined self-reported physical activity at two time points (1995 and 2005-6). In total, 61,256 participants were included in the analysis with notable exclusion criteria, including history of stroke or age less than 26 years old. Exercise was reported as moderate (e.g. brisk walking) or strenuous (e.g. swimming, running) and quantified as hours per week and months per year in the past 3 years. The authors used this data to then establish average minutes/week and dichotomized the measures by the AHA recommendations for moderate (150 minutes/week) or strenuous (75 minutes/week) activity. Using these metrics of physical activity, the authors assessed incident stroke risk.
First, they explored the association between incident stroke risk and physical activity reported at the 10-year follow-up questionnaire. Interestingly, engaging in moderate but not strenuous physical activity was associated with a lower risk of total stroke (HR 0.84, 95%CI 0.73-0.96) when adjusted for hypertension, diabetes, hyperlipidemia and tobacco use. This observation was driven by a reduced risk in ischemic (HR 0.0.82, 95%CI 0.70-0.96) rather than hemorrhagic stroke (HR 0.93, 95%CI 0.70-1.23).
The authors then investigated the impact of longitudinal physical activity on incident stroke risk. In those individuals that met the AHA recommendations for moderate exercise at both time points, there was a reduced risk of fatal stroke (HR 0.62, 95%CI 0.43-0.90). Interestingly, in individuals that only met the AHA recommendations for moderate exercise on follow-up, there was a reduced risk of all and ischemic stroke (HR 0.70, 95%CI 0.55-0.88) compared to individuals that did not meet recommendations at both time points. Individuals that met the AHA guidelines at baseline but not on follow-up, however, did not demonstrate any reduced risk in incident stroke.
The results of this study further support the argument that physical activity has a beneficial contribution on incident stroke risk reduction. There are several questions regarding the results of this analysis, however, that merit consideration in the overall interpretation of the results. First, why was moderate but not strenuous physical activity associated with reduction in risk of total and ischemic stroke? Secondly, why was there no observed risk reduction in stroke for individuals that met AHA recommendations at both time points? The authors suggest that it may be a power issue given that most participants endorsed moderate activity, rather than strenuous activity, and only 1/3 of participants met the AHA recommendations for physical activity at both time points. This discrepancy, however, does complicate the interpretation and certainly merits further investigation. Ultimately, what can be inferred from these results is that later life, moderate physical activity has a beneficial effect on incident stroke risk. Clinicians should, therefore, continue to emphasize the importance of physical activity as one part of a multi-faceted approach to stroke prevention.