Physical Activity Frequency and Risk of Incident Stroke in a National US Study of Blacks and Whites

McDonnell MN, Hillier SL, Hooker SP et al.
Stroke. 2013;44. DOI: 10.1161/STROKEAHA.113.001538

Background

Stroke is a leading cause of disability and mortality in the United States [1]. Healthy life style choices are known to reduce stroke risk [2]. An important component of a healthy life style is physical activity (PA). A recent investigation revealed that 49% of Americans do not meet the PA guidelines [3].
A multinational case-control study (INTERSTROKE) revealed that physical inactivity was the second leading risk factor for stroke after hypertension, with a population-attributable risk of 28.5% [4]. The precise amount and type of exercise required to reduce stroke risk is unknown, meta-analyses suggested that regular PA reduces  the risk of stroke by 25-30% in comparison to the least active people [5,6].
Recent evidence suggests that the effect of vigorous PA on stroke risk may differ between men and women, with a lack of risk reduction in women [7]. This study aims to investigate the potential for self-reported PA to reduce incident stroke in a large, multiracial prospective cohort of men and women. Data of 29017 participants of the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study were used for this analysis. During a mean follow-up of 5.7 years, 918 incident stroke and TIAs occurred. 

Main results

• After correction for age, sex, race and age-race interaction, the HR for stroke/TIA for those not undertaking PA, as compared to people who engaged in PA >4x per week, was 1.20 (95%CI: 1.02-1.42). People who did PA 1-3x per week, showed HR: 1.16 (95%CI: 0.98-1.42). Further adjustment for region, urban/rural residence and socioeconomic status hardly changed these associations.
• No statistically significant interaction between sex and PA was seen in this analysis (P=0.22), possibly due to insufficient power.
  When stratifying the results by sex, men with 1-3x PA per week had a greater incidence of stroke than men who exercised >4x per week (HR: 1.30, 95%CI: 1.05-1.61 and HR: 1.21, 95%CI: 0.95-1.53 for 0 PA per week, P=0.09 for trend in the demographic model, and in the socioeconomic status model: HR: 1.26, 95%CI: 1.00-1.59 and HR: 1.16, 95%CI: 0.90-1.49 for men not engaging in PA, no changes upon further correction for stroke risk factors).
  In women, however, no significant association was seen between PA and incident stroke, except for a trend towards a reduced risk upon 1-3x or >4x PA per week, as compared to none.

Conclusion

These findings confirm that regular physical activity is associated with a decreased risk of incident stroke and TIA. The extra protective effect of >4x PA per week, in comparison to 1-3x, did not reach statistical significance. PA appears to interact with other risk factors for stroke, as the effect was attenuated slightly upon correction for other common risk factors. This was the first large cohort that studied the effect of PA on stroke that included as many men as women. No protective effect of PA on stroke risk was seen for women, while in men trends were seen for higher risks for 1-3x PA per week, as compared to >4x per week, but not for 0 PA.

References

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