Source: American Physiological Society. A new New Year's reason to work out: Exercise improves three measures of heart protection
For decades, hormone replacement therapy (HRT) was prescribed for postmenopausal women to protect them from cardiovascular disease (CVD). However, results from the Women's Health Initiative questioned its effectiveness, which has led to more caution in prescribing and using HRT for this purpose. So, are there other ways women can decrease their risk of heart disease? Yes – and new evidence shows that exercise may be the easiest.
According to a new study, women who are more physically fit have better blood clotting profiles than women who are unfit. These positive results were evident in three different measures of the hemostatic (blood clotting) system that have previously been linked to heart attacks. Lead author Linda Szymanski explains: "Everyone benefits from being physically fit, regardless of whether they are on HRT or not. This is particularly good news for women who are either unwilling or unable to take HRT because they can gain cardioprotective benefits by becoming physically fit. You want as many reasons as you can to get people out there to exercise. "In our study, fitness provided benefits that are not as obvious and are not usually measured by doctors or health clubs, unlike cholesterol, blood pressure, or body weight."
Szymanski got the idea for this study because "We all know exercise is linked with reduced heart attacks. Everyone says this is because exercise lowers your cholesterol, etc., but the bottom line is it's usually a blood clot that causes a heart attack." The researchers thought exercise must have other benefits and so they tested blood-clotting variables, including clotting and fibrinolysis – the ability to prevent or break up blood clots. The study, "Relationship of physical fitness, hormone replacement therapy and hemostatic risk factors in postmenopausal women," was conducted by Linda M. Szymanski, Craig M. Kessler and Bo Fernhall. The research appears in the online edition of the Journal of Applied Physiology, published by the American Physiological Society. In this study, a number of blood clotting variables were studied in four groups of women (12 in each group) – women on HRT who were fit and unfit, and women not taking HRT who were fit and unfit, before and after a maximal exercise test. The well-known "stress test" is usually used to diagnose or test for heart disease, or to find out how fit someone is before allowing him or her to embark on an exercise program. In this case the stress test was to check how the blood clotting system reacted – and unfit women didn't respond well by any measure. Tissue plasminogen activator (TPA), an enzyme made by the body that breaks up blood clots, was higher in physically fit women compared to unfit women. Plasminogen activator inhibitor-1, a blood substance that inhibits TPA, was lower in physically fit women. And, a marker that indicates blood clot activation — prothrombin fragment 1+2 — was also lower in fit women. Together these results suggest that exercisers may be better able to prevent the formation of blood clots, and may be one reason why exercisers are less likely to have heart attacks.
Next steps The authors note that although the correlations in the study between general fitness and healthy blood clotting measurements are very strong, the results are essentially a "snapshot" of current health conditions and associations, but don't prove a cause-and-effect relationship. The authors are currently conducting longitudinal studies to further examine the relationship between exercise and blood clotting, and other cardiovascular risk factors. Szymanski, who now is a third-year resident in gynecology and obstetrics, noted that the "Women's Health Initiative made everyone think more carefully about hormones and many women are now more cautious about starting hormones. Therefore, other ways to improve heart disease risk are needed." Despite the inherent limitations to the cross-sectional study, the authors emphasize that their research shows that "increased physical fitness is associated with risk reducing hemostatic profiles in postmenopausal women, which may lead to significant health benefits."
Source and funding The study, "Relationship of physical fitness, hormone replacement therapy and hemostatic risk factors in postmenopausal women," was conducted by Linda M. Szymanski, Craig M. Kessler and Bo Fernhall. The research appears in the online edition of the Journal of Applied Physiology, published by the American Physiological Society. The study was carried out when the three authors were at George Washington University, Washington D.C. Currently, Szymanski is at the Department of Gynecology and Obstetrics at Johns Hopkins Medical Center, Baltimore; Kessler is at Georgetown University Medical Center, Washington, D.C.; Fernhall is at the University of Illinois, Champaign (and was at Syracuse University when the paper was submitted). Research was supported in part by a grant from the Life Fitness Academy, which supports research by young faculty and graduate students. Life Fitness, which makes exercise equipment, is a subsidiary of Brunswick Corp.
The American Physiological Society was founded in 1887 to foster basic and applied bioscience. The Bethesda, Maryland-based society has more than 10,000 members and publishes 14 peer-reviewed journals containing almost 4,000 articles annually. APS provides a wide range of research, educational and career support and programming to further the contributions of physiology to understanding the mechanisms of diseased and healthy states. In May, APS received the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring (PAESMEM).