A new analysis of activity and health in older women highlights sitting as an independent risk factor for cardiovascular disease (CVD). The study was published on April 9 in the Journal of the American College of Cardiology and found that women who reported sitting more than 10 hours per day were at an 18 percent increased risk for CVD compared to women who sit less than five hours per day regardless of physical activity levels. Women who spent more time sitting and also were physically inactive were at 63 percent higher risk for CVD.

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While it has long been known that lack of leisure-time physical activity increases the risk for coronary heart disease (CHD), the effect of sitting has been less clear. The Women's Health Initiative Observational Study looked at a total of 71,018 postmenopausal women without a history of CVD, aged 50 to 79 years at entry, who were enrolled in the study between 1994 and 1998 across 40 U.S. clinical centers. The women were followed for a median of 12.2 years using a baseline physical exam, medical record reviews and self-administered questionnaires at regular intervals.

The primary endpoints for the analysis were incident CHD, including nonfatal MI, fatal CHD, and stroke. Between study enrollment and September 2010, women in the group had a total of 2,411 incident cases of CHD, 2,050 incident strokes and 4,235 first CVD events. Both sitting time and decreased physical activity were positively associated with increased risk of CHD and stroke.

The hazard ratio for sitting more than 10 hours daily was 1.18 (p for <0.001) compared to sitting less than five hours daily. Using the highest physical activity group as the reference point, the hazard ratio for medium physical activity was 1.16; for low physical activity it was 1.30; for inactivity it was 1.47 (p for trend <0.001). The hazard ratio for physically inactive women who sat more than 10 hours daily was 1.63.

"Physiological responses associated with prolonged sitting, such as suppression of skeletal muscle lipoprotein lipase activity, which is necessary for triglyceride uptake and high-density lipoprotein cholesterol production, and reduced glucose uptake, might explain the independent effect of sedentary behavior on cardiovascular disease risk factors and also on cardiovascular disease risk," said Andrea Chomistek, ScD, Harvard School of Public Health, Boston. "In addition to reducing sitting time, taking breaks during prolonged periods of sitting, i.e. by standing up and taking short walks, might be beneficial in reducing cardiovascular disease risk. For individuals who are unable, or averse, to exercise, amount of time spent sitting may be more amenable to change than increasing levels of physical activity."

"Given the projected population growth of U.S. women and the relatively high prevalence of physical inactivity, the present findings have important public health implications," he added.

Keywords: Stroke, Muscle, Skeletal, Exercise, Women's Health, Coronary Disease, Risk Factors, Medical Records, Glucose, Prevalence, Cholesterol, Lipoprotein Lipase, Cardiovascular Diseases, Sedentary Behavior, Surveys and Questionnaires, United States

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