More exercise equals lower risk of ischemic stroke

Even in an Asian nation where people generally have higher levels of physical activity on the job than is typical in North America or Europe, those who walk more or engage in regular sports activity tend to have lower levels of ischemic stroke and coronary heart disease, according to a new study in the Nov. 1, 2005, issue of the Journal of the American College of Cardiology.

"The strength of the present study is a statistical power sufficient to detect the effects of physical activity on mortality from cardiovascular disease. We found a significant inverse association between time spent walking and the risk of ischemic stroke in addition to an inverse relationship between sports participation and risk of coronary heart disease in Asian countries, where job-related physical activity is generally higher than in Western countries," wrote the authors, including Hiroyuki Noda, M.D. and Hiroyasu Iso, M.D., from the University of Tsukuba in Ibaraki and the Graduate School of Medicine at Osaka University in Osaka, Japan.

The researchers used data collected as part of a large population study of cancer risk in Japan. Between 1988 and 1990, 31,023 men and 42,242 women aged 40 to 79 years in 45 communities across Japan were given a questionnaire about their lifestyles and medical histories. The participants had no history of stroke, coronary heart disease or cancer. Through 1999, almost 2,000 participants died of cardiovascular disease. For this analysis, the researchers separated the participants into four categories according to the amount of daily walking or weekly sports activity they reported.

Consistent with results of studies done in North America and Europe, those who walked a least an hour a day or engaged in sports at least five hours per week had age-adjusted death rates from cardiovascular disease that were 20 to 60 percent lower than those in the second-lowest category of reported physical activity. Specifically, physical activity was associated with reduced risk of ischemic stroke (stroke caused by a blood clot or other blood flow blockage), coronary heart disease and total cardiovascular disease. There was no statistically significant relationship between physical activity and the risk of a stroke caused by bleeding (either intraparenchymal hemorrhage or subarachnid hemorrhage).

"Limitations of the present study included the fact that we did not have systematic information on pre-clinical disorders that prevented the participants from walking or participating in sports. This might have lead to a bias of cause-effect reversal, even though most of the subjects were apparently healthy," the authors wrote.

In order to try to avoid such bias, the researchers used the group with the second-lowest activity level as the reference group, rather than compare those with high levels of physical activity to those with the lowest levels. Thus they hoped to prevent a possibly misleading comparison with people who didn't exercise because they were already ill. The researchers also analyzed the data after excluding anyone who died within two years of the beginning of the study, in order to allow a reasonable amount of lead time for physical activity to potentially have an effect on the health of study participants.

Interestingly, the analysis suggested that walking and sports may have different effects.

"Our data suggest a potential differential effect of walking versus sports participation on ischemic stroke and coronary heart disease risk. We found that participation in sports was associated with a reduced mortality due to coronary heart disease, but this association did not exist with walking time. Walking time, however, was associated with a reduced risk for mortality from ischemic stroke, but sports participation was not," they wrote.

By demonstrating an association between walking or sports and reduced cardiovascular disease deaths in this Asian population, similar to the results of studies in Western nations, despite differences in average levels of job-related physical activity, the researchers conclude that "the present study provides epidemiological evidence that engaging in physical activity through walking and sports participation might reduce risk of mortality from ischemic stroke and coronary heart disease among Japanese men and women."

Russell V. Luepker, M.D., F.A.C.C., at the University of Minnesota in Minneapolis, who was not connected with this study, noted the strengths of the study design and the valuable health message in the results.

"Important strengths of this study include the large number of participants, the inclusion of both leisure and work activity and the extended follow-up period. The use of prevalent cases, short-term mortality and the use of the second lowest exercise category as referent minimizes the effects of those who do not exercise because they are already ill. The graded reduction of coronary heart disease and stroke mortality associated with increasing levels of walking and sports sends a strong message supporting regular physical activity recommendations. The adjustment for other cardiovascular risk factors strengthens the relationship's validity," Dr. Luepker said.