Cardiovascular Benefits of Exercise Depend Little on Weight Loss

BOSTON, Oct. 23 -- Visible improvements in weight may be less important to the cardiovascular benefit of regular exercise than modest improvements in inflammation and hemostasis, researchers found.Weekly physical activity was associated with a 27% to 41% reduction in women's cardiovascular disease risk, according to an analysis of the Women's Health Study reported online in Circulation: Journal of the American Heart Association.
But body mass index changes contributed only 10% of the improvements in cardiovascular risk, said Samia Mora, M.D., M.H.S., of Harvard and Brigham and Women's Hospital, and colleagues.
Surprisingly, inflammatory and hemostatic biomarkers accounted for about one-third of the reduced risk. Blood pressure effects accounted for another quarter of the risk reduction.
"Until this study, the way physical activity results in cardiovascular benefits long-term has really been a black box," Dr. Mora said in an interview with MedPage Today.
These findings should "encourage patients that even if they don't lose weight, physical activity has many other benefits on a number of different pathways, all of which combine together to lower cardiovascular events," she said.
The researchers analyzed outcomes for 27,055 participants in the larger Women's Health Study of low-dose aspirin and vitamin E for primary prevention of cardiovascular disease.
The women were apparently healthy female healthcare professionals 45 or older and free of self-reported cardiovascular disease and cancer at baseline from 1992 through 1995 and who provided a blood sample and completed a questionnaire on physical activity. Participants completed follow-up questionnaires every six or 12 months.
Over a mean 10.9 years of follow-up, there were 979 first cardiovascular disease events, which were mostly coronary heart disease events (253
MIs, 398 percutaneous coronary interventions, and 219 coronary artery bypass grafts) but also included 266 ischemic strokes.
Only modest changes were seen in individual risk factors with physical activity (about 5% for blood lipids, 3 to 5 mm Hg for blood pressure, and 1% for hemoglobin A1c).
But, there were large improvements in cardiovascular disease risk.
Compared with 200 kcal or less exercise per week, incident cardiovascular disease risk decreased linearly as physical activity increased to 200 to 599 kcal, 600 to 1,499 kcal, and 1,500 kcal or more per week (27%, 32%, and 41% reduction, respectively, P<0.001 for trend).
Overall, 59% of the association between physical activity and cardiovascular disease risk was explained by traditional and novel risk factors measured in the study. The proportion of risk attributed to each factor was:
32.6% for inflammatory and hemostatic biomarkers (high-sensitivity C-reactive protein, fibrinogen, and soluble intracellular adhesion molecule-1)
27.1% for blood pressure
15.5% for novel lipid parameters (lipoprotein [a] and apolipoprotein A1 and B-100)
19.1% for traditional lipid parameters (total, LDL, and HDL cholesterol)
10.1% for body mass index
8.9% for hemoglobin A1c and diabetes status
Less than 1% for homocysteine and creatinine
Less of the coronary heart disease risk reduction was explained by these risk factors (35.5% versus 59.0% for cardiovascular disease overall), but the pattern of contributing factors was similar.
Likewise, results were similar when activity was calculated in MET-hours per week instead of kilocalories per week, except that body mass index became a more important contributor to risk reduction (21.9%) as did hemoglobin A1c and diabetes (12.2%).
"The mechanisms underlying the chronic anti-inflammatory and hemostatic effects of exercise are not well defined and are only partially related to body weight," the researchers noted.
The remainder of the risk reduction unexplained by these known risk factors could be attributed to unmeasured factors, such as heart rate and heart rate recovery, or could be explained by the same risk factors if they were better measured, said Dr. Mora.
She and her colleagues concluded that even moderate levels of exercise-"at least 600 kcal per week, or the equivalent of just over 2 hours per week of brisk walking, consistent with current guideline recommendations"--lowers risk of clinically important cardiovascular disease events.
While the results need to be confirmed for men as well, moderate exercise "may have important downstream consequences for the primary prevention of cardiovascular disease," they wrote.
The analysis was supported by grants from the Donald W. Reynolds Foundation, Leducq Foundation, and Doris Duke Charitable Foundation. The Women's Health Study is supported by grants from the National Heart, Lung, and Blood Institute and the National Cancer Institute and philanthropic support from Elisabeth and Alan Doft and their family.

Primary source: Circulation: Journal of the American Heart AssociationSource reference: Mora S, et al "Physical Activity and Reduced Risk of Cardiovascular Events: Potential Mediating Mechanisms" Circulation 2007 ; 116.