Replacing Sedentary Time With Light Physical Activity Can Improve BMD, Reduce Osteoporosis Risk

Substituting 30 minutes of sedentary time with light physical activity may improve bone mineral density (BMD) and reduce the risk for osteoporosis in postmenopausal women, according to study results published in European Journal of Sport Science. Furthermore, the benefit was more pronounced in older and overweight women.

Previous studies have shown physical activity is associated with increased BMD and may assist in the efforts to prevent osteoporosis. However, there are no data regarding the effects of substituting sedentary behavior with different types of physical activity on the risk for osteoporosis, and data are scarce about the quantity of time and intensity of physical activity required to have an impact on BMD in older women.

In this study, the researchers used data from the National Health and Nutrition Examination Survey (NHANES) to assess the effects of replacing sedentary time with physical activity on BMD. Substitution analysis was applied to estimate BMD and osteoporosis risk for women replacing 30 minutes of sedentary time with 30 minutes of light physical activity.

The study included individuals who participated in the NHANES surveys conducted from 2003 to 2006. Of 20,470 participants, the researchers identified 2382 women aged ≥50 years. They excluded patients with missing data on physical activity, BMD measurements, or other covariates. The final study cohort included 1052 women (median age, 59.1; 58.5% white; 70% overweight).

Replacing 30 minutes of sedentary time with an equal amount of light physical activity was associated with increased BMD (2.70 mg/cm² in the total body, 3.75 mg/cm² in the pelvis, 2.44 mg/cm² in the trunk, 3.17 mg/cm² in the thoracic spine, and 1.97 mg/cm² in the legs). The benefits of substituting sedentary time with physical activity were more pronounced in overweight and older women.

In a similar fashion, replacing 30 minutes of sedentary time with physical activity was associated with a 12% reduced risk for osteoporosis in the entire cohort. In women age >65, the risk reduction was greater, including a 22% reduced risk for thoracic spine osteoporosis. In overweight women, there was a 16% risk reduction for thoracic spine osteoporosis after substituting 30 minutes of sedentary time with physical activity.

There was no statistically significant interaction between the time spent in light physical activity and osteoporosis risk according to age or body mass index. In addition, there was no clear benefit for BMD associated with substituting sedentary time with moderate to vigorous physical activity.

The researchers acknowledged several limitations of this study, including the cross-sectional design and observational nature, which do not allow establishment of causality.

“The present work implies an improvement in bone mineral density for postmenopausal women who substitute 30 min of sedentary time with an equal amount of light physical activity,” concluded the researchers.

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Reference

Ricci C, Gervasi F, Havemann-Nel L, Smuts CM, Kruger SH, Leitzmann MF. 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. Eur J Sport Sci. doi:10.1080/17461391.2019.1600588