Failing to regularly work up a sweat through exercise may raise risks for a stroke or transient ischemic attack (TIA), a new study confirms.

The study found that participants who were inactive had a 20% increased risk for stroke compared with those who exercised 4 or more times per week, and that those who were active 1 to 3 times a week were 16% more likely to suffer a stroke.

“The point here is that you should be exercising 4 times a week at least and doing it hard enough so that you’re getting a bit of a sweat,” lead author Michelle N. McDonnell, PhD, lecturer, rehabilitation, University of South Australia, Adelaide, toldMedscape Medical News.

The study was published online July 18 in Stroke.

Sweat Question

The Reasons for Geographic and Racial Differences in Stroke (REGARDS) is a population-based, longitudinal study of 30,239 Americans aged 45 years or older, with oversampling of blacks and residents of the Stroke Belt, an area in the southeastern United States that has a relatively higher stroke mortality rate.

 
Dr. Michelle N. McDonnell

Participants were asked how many times a week they engaged in physical activity intense enough to work up a sweat. Researchers categorized responses into 3 groups: no times per week, 1-3 times per week, and 4 or more times per week. One third of participants reported exercising less than once a week.

The question about exercise-related sweating is easy to answer, and responses correlate well with fitness level, said Dr. McDonnell. “It’s really biasing towards more vigorous activity, which we know is important.”

Researchers verified strokes through medical records and classified them into ischemic or hemorrhagic. The 27,348 participants, who were stroke free at the start of the study, were followed for a mean of 5.7 years.

The study found that compared with those who hit the gym, biked to work, or were similarly active at least 4 times a week, the hazard ratio (HR) for stroke/TIA for those undertaking no physical activity was 1.20 (95% confidence interval [CI], 1.02 – 1.42) after adjustment for age, sex, race, and age-race interaction. For 1 to 3 times per week, the HR was 1.16 (95% CI, 0.98 – 1.42).

After also controlling for region, urban/rural residence and socioeconomic status, the significant association remained, with similar HRs.

There seemed to be a dose-dependent relationship, with exercising 1 to 3 times per week providing less protection against stroke than for boosting that to 4 or more times a week.

Risk Factors

After adjustment for stroke risk factors, the effect was reduced by 30% to 1.14 (CI, 0.95 – 1.37) and was statistically insignificant. “This tells us that exercise seems to be working by reducing blood pressure and reducing obesity and perhaps helping with controlling diabetes, so exercise is working on lots of things all at the same time,” commented Dr. McDonnell.

Those in the study who were more physically active were generally more fit, had lower blood pressure; and were less overweight or obese judging from body mass index (BMI) data, although, unexpectedly according to the authors, they tended to drink more alcohol.

Physical activity also has direct biological effects that could be protective against stroke. According to Dr. McDonnell, it improves circulation and endothelial function, and reduces platelet activity to help prevent formation of blood clots, in addition to enhancing brain function.

Other research suggests that people who are more physically active who suffer a stroke have a less severe episode and will recover much better than those who are inactive, added Dr. McDonnell.

When looking at the effects of sex, the authors found that men who took part in physical activity 1 to 3 times per week had a greater incidence of stroke compared with those who exercised 4 or more times per week (HR for demographic model, 1.30; HR for socioeconomic status model, 1.26).

“In men, those who exercise 3 times a week didn’t have the same benefits as those who exercised 4 or more times a week, suggesting that for men in particular it’s that 4 times a week, rigorous activity that is really important,” said Dr. McDonnell.

In contrast, there was no significant association between physical activity and incident stroke in women, although there was a trend to a similar reduced risk for those who exercised at least some compared with none.

Results in this study were similar for ischemic and hemorrhagic strokes. The study found no interaction between race and physical activity.

Duration Question

The study does not settle the question of exactly how much exercise during those 4 weekly sessions is optimal to protect against stroke.

“There has been lot of research saying that if you cut smoking, this will be your benefit, or if you cut your blood pressure by 5 millimeters of mercury, you’re going to cut your risk by this much, but it’s much harder when it comes to physical activity,” said Dr. McDonnell. “We still need more research to determine, for example, whether if you do 15 minutes of exercise versus 30 minutes, you’re still going to get the same benefit.”

For ideal cardiovascular health, the American Heart Association recommends 150 minutes of moderate-intensity exercise per week, which could be 30 minutes 3 times per week. Some organizations suggest 30 minutes 5 days a week.

In addition to failing to quantify the duration or type of physical activity or the precise number of sessions, the study was limited in that stroke events occurred several years after classification of physical activity and activity habits may have changed in the interim. The study also didn’t capture persons who had a stroke but did not seek medical care.

As well, the sweat question used in the study prevented inclusion of such moderate-intensity physical activities as walking or cycling. This might explain the inability to find a stronger association between physical activity and stroke in women, said Dr. McDonnell.

REGARDS researchers are now doing additional in-home interviews with participants to try to tease out more useful information about length and levels of physical activity, said Dr. McDonnell.

The study results should encourage doctors to stress the importance of exercise when speaking with patients, Virginia Howard, PhD, senior author of the study from the School of Public Health, University of Alabama at Birmingham, said in a release from the National Institutes of Health, which funded the study.

“Physical inactivity is a major modifiable risk factor for stroke,” said Dr. Howard. “This should be emphasized in routine physical check-ups along with general education about the benefits of exercise on stroke risk factors including high blood pressure, diabetes and being overweight or obese.”

Accounting for Sedentary Behavior

Asked to comment on the study, Joshua Z Willey, MD, assistant professor, neurology, Columbia University, New York, said the results could affect clinical practice, although it would be even better to have information on optimal length of exercise sessions.

“It’s something simple that you can ask patients in the clinic — do you exercise 4 times a week enough to break a sweat?”

The message about the benefits of regular physical activity applies not just to stroke but to other conditions as well, for example, arthritis and cognition, Dr. Willey pointed out.

 

One benefit of the study was that it didn’t limit the physical activity to leisure time pursuits, said Dr. Willey. “The authors accounted for the exercise people could do at work or the exercise that people do when they commute, for example being on a bike.”

Dr. Willey noted that there are still unanswered questions regarding the effect of exercise on stroke risk. For example, he said, some studies suggest an effect of the amount of time spent in sedentary activities.

“Future analyses need to account for the percentage of sedentary behavior. What is the impact if you exercise once a week for 75 minutes but you spend the rest of your time sitting on the coach watching TV?”

Dr. McDonnell is supported by a National Health and Medical Research Council of Australia Fellowship. The study was supported by a grant from the National Institute of Neurological Disorders and Stroke.

Stroke. Published online July 18, 2013. Abstract