Moderate fitness levels protect against stroke

Men and women with moderate levels of cardiorespiratory fitness may be at significantly reduced risk of stroke, according to the findings of a large, prospective study with long-term follow-up.

More than 46,000 men and nearly 15,300 women aged 18-100 years participated in the study and were followed for an average of 18 years. Participants underwent a baseline physical examination between 1970 and 2001 and at enrollment, had no known history of MI or stroke, had a normal resting electrocardiogram, and could achieve at least 8.5 percent of the age-predicted maximal heart rate during a treadmill exercise test, it was reported at International Stroke Conference 2008.

During the follow-up period, 692 strokes occurred in the men, and 171 occurred in the women. Significant linear trends between fitness levels and the rates of total strokes and nonfatal stroke were found in both men and women, and between fitness levels and the rate of fatal stroke in men, after adjustment for such demographic and biological factors as age examination year, smoking, family history of cardiovascular disease, and body mass index.

The risk of total stroke was reduced by 40 percent in men in the highest fitness level quartile, compared with those in the lowest quartile, and by 43 percent in women in the highest fitness quartile, compared with those in the lowest (hazard ratios of 0.6 and 0.57, respectively), director of the Prevention Research Center at the University of South Carolina, Columbia, noted at the conference, sponsored by the American Stroke Association.

The risk of nonfatal stroke was reduced by 38 percent in men and 44 percent in the women (HR 0.62 and 0.56, respectively) when comparing those in the highest and lowest fitness quartiles.

As for the fatal stroke rates, 186 fatal strokes occurred in men, and only 55 occurred in women in the study. The risk of men in the highest, compared with the lowest, fitness quartiles was significantly reduced by 50% (HR 0.5), but the difference between the rates in women in those quartiles (nearly 60%, HR 0.42) was not significant, most likely because the study wasn’t powered to detect a significant difference because of the small number of fatal strokes in women.

They (saw) noticeable drop in the rate of stroke at a fitness level associated with 7-8 METs (metabolic equivalents) based on their maximal treadmill test to exhaustion. Interestingly, beyond that point, there is no further decline in total stroke rate. Noting that pattern was the same in men and women.

The study was the first to show a significant independent association between cardiorespiratory fitness and fatal and nonfatal stroke in men and nonfatal stroke in women, and one of few to use objective measures of fitness rather than self-reported physical activity levels. It shows a dramatic reduction in stroke incidence at those fitness levels, which are actually low levels of fitness for younger patients and moderate levels for older patients and which were seen in the lowest fitness quartile in the men and the second lowest in the women in this study.

Basically, if folks are participating in some kind of physical activity that would meet current guidelines and recommendations for adults, brisk walking for 30 minutes 3 times a week they would probably be able to attain and/or maintain that level of fitness, so there’s some hope here for a lot of people out there.

The study has a number of strengths but is limited by the fact that nonfatal strokes were self-reported (although in those for whom medical records were verified, the agreement rate between self-reports and records was 89 percent), the inability to adjust for dietary and medical issues and changes in fitness levels over time, and the fact that participants were most white, well-educated, and had middle to upper level incomes, thus limiting the generalizability of the findings to populations.

Among those strengths were the use of a baseline examination to detect clinical disease, the number of measured risk factors, and the large number of person-years of follow-up (about 800,000 for men and 250,000 for women).