In a recent study published in the Scientific Reports Journal, researchers compared the associations of sedentary and physical activities with factors such as body fat percentage and bone mineral density among the United States (U.S.) population.
Study: Correlation between sedentary activity, physical activity and bone mineral density and fat in America: National Health and Nutrition Examination Survey, 2011–2018. Image Credit: baranq/Shutterstock.com
Background
Osteoporosis, characterized by the reduction in bone density and bone microstructure deterioration and the consequent increase in the incidence of skeletal fractures, is a growing health burden in the U.S. and worldwide.
The factors that result in the decrease in bone mineral density are multifaceted and involve substantial changes in nutrition and sex hormones. Other factors such as physical activity levels, smoking behavior, and dietary intake also influence the development of osteoporosis with age.
Processes such as homeostasis and bone turnover are influenced by periods of bed rest or reduced gravity, and studies have reported that physical activity or sedentary habits result in varying effects on bone density in males and females.
While some findings indicate that physical activity is associated with improvements in hip bone mineral density among men, others report no such correlations in women.
In contrast, some studies also report a negative correlation between sedentary activity and bone mineral density among women. Furthermore, sedentary and physical activities are also associated with changes in the total fat percentage in the body, but the results for different age groups have been inconsistent.
About the study
In the present study, the researchers analyzed data from the National Health and Nutrition Examination Survey (NHANES), which conducted multistage sampling to examine the health and nutrition status of the civilian population of the U.S.
From the data spanning the years between 2011 and 2018, the study excluded participants for whom information on lumbar spine bone density measurements and time spent doing sedentary activities was missing.
Data on participants with diseases such as cancer, rheumatoid arthritis, thyroid disease, and liver disease, which could impact bone mineral density, were also excluded.
Sedentary and physical activity were the independent variables in the analysis, while bone mineral density and total fat percentage were the dependent variables.
The information on physical and sedentary activities was collected through structured questionnaires. It was determined based on the hours spent a day performing vigorous or moderate physical activity or being sedentary, respectively. Dual-energy x-ray absorptiometry measured the total fat percentage and bone mineral density.
Sociodemographic information on age, sex, race and ethnicity, and education levels were also obtained, as were data on smoking behavior and alcohol intake. Blood biochemical tests measured cholesterol, calcium, total protein, urea nitrogen, blood phosphorous, vitamin D, and serum uric acid levels.
Multiple linear regression models were used to evaluate the association between the independent and dependent variables while adjusting for confounding variables.
Results
The results reported that sedentary activity was positively correlated with total fat percentage while showing negative associations with lumbar bone mineral density after adjusting for confounding factors such as age, race and ethnicity, smoking, alcohol intake, body mass index, and levels of total protein, blood urea nitrogen, blood phosphorous, vitamin D, and serum uric acid levels.
Furthermore, physical activity showed a negative association with total body fat and a positive correlation with bone mineral density.
The researchers also discussed how the increase in sedentary activity could exacerbate the loss of bone mineral density by reducing exposure to sunlight and disrupting homeostasis in the skeletal system.
Other studies have also reported the increased production of the parathyroid hormone due to sedentary behavior, which impacts the calcium metabolism essential for bone formation.
The decrease in mechanical stimulation due to sedentary habits is also believed to be linked to weakened periosteal attachment and bone density loss, with the lack of physical activity having a direct negative impact on osteogenesis.
The results found the association between physical activity and bone mineral density to be stronger in men than women, which could potentially be explained by the coupled association between muscle mass and bone remodeling as described by Wolfe’s law on bone formation.
Conclusions
Overall, the findings suggested that sedentary lifestyles and habits had a negative impact on bone mineral density and increased the total fat percentage of the body.
At the same time, physical activity was linked to an increase in bone mineral density and lower total fat percentage.
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