Substitution of sedentary time with light physical activity is related to increased bone density in U.S. women over 50 years old. An iso-temporal substitution analysis based on the National health and Nutrition Examination Survey.

U.S. women are ageing. This is causing rises in osteoporosis prevalence and risk of fracture with related increases in health care costs. Replacing sedentary time with light physical activity may represent a cost effective public health solution to osteoporosis in elderly women. The National Health and Nutrition Examination Survey conducted over the period 2003-2006 provided cross-sectional data on bone mineral density and objectively assessed physical activity among 1,052 women aged 50-85 years old. Substitution analysis was applied to estimate increased bone mineral density and reduced osteoporosis for those women replacing 30 min of sedentary time with an equivalent amount of light physical activity. Substitution of 30 min of sedentary time with an equal amount of light physical activity was associated with increased bone mineral density of about 3 mg/cm2 and a 12% reduced risk of osteoporosis in the spine. When considering overweight women and women over 65 years of age, this association was reinforced and it extended to the pelvis, legs and trunk, resulting in a consistent bone mineral density increase of about 3-6 mg/cm2. The substitution of 30 min of sedentary time with an equal amount of light physical activity appears a possible primary prevention method to reduce osteoporosis and related increases in risk of fracture, mortality, and health care costs in women over 50 years old.