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Physical activity and stroke incidence: the Harvard Alumni Health Study.

BACKGROUND AND PURPOSE
Physiologically, it appears plausible for physical activity to decrease stroke risk; however, epidemiological studies have produced mixed findings. Furthermore, few studies have examined specific kinds and intensities of activities. The purpose of this study was to examine the association between physical activity, including its various components (walking, climbing stairs, participation in sports and recreational activities), and stroke risk.


METHODS
This was a prospective cohort study of 11 130 Harvard University alumni (mean age, 58 years) without cardiovascular disease and cancer at baseline. Men reported their walking, stair climbing, and participation in sports or recreation on baseline questionnaires in 1977. Stroke occurrence was assessed with another questionnaire in 1988. Death certificates were obtained for decedents through 1990 to determine strokes not previously reported (total strokes=378). We used Cox proportional hazards regression to estimate the relative risks and 95% CIs for stroke occurrence associated with physical activity.


RESULTS
After adjustment for age, smoking, alcohol intake, and early parental death, the relative risks of stroke associated with <1000, 1000 to 1999, 2000 to 2999, 3000 to 3999, and >/=4000 kcal/wk of energy expenditure at baseline were 1.00 (referent), 0.76 (95% CI, 0.59 to 0.98), 0.54 (0.38 to 0. 76), 0.78 (0.53 to 1.15), and 0.82 (0.58 to 1.14), respectively; P=0. 05 for linear trend. Walking >/=20 km/wk was associated with significantly lower risk, independent of other physical activity components. Climbing stairs and activities of at least moderate intensity (>/=4.5 METs, or multiples of resting metabolic rate) each showed U-shaped relations to stroke risk, with the risk being significantly lower at the nadir of the curve. Light intensity activities (<4.5 METs), however, were unrelated to stroke risk.


CONCLUSIONS
Physical activity is associated with decreased stroke risk in men. A decreased risk was observed at energy expenditures of 1000 to 1999 kcal/wk, with further risk decrement seen at 2000 to 2999 kcal/wk but not beyond. Confirmation of the U-shaped relation observed in these data requires similar observations in other populations.