Volume 15, Number 10
It seems like sitting should be good for the human body. There is little risk of musculoskeletal injury with sitting, and little stress on the cardiovascular and respiratory systems. However, study after study finds that being sedentary is associated with higher risk of numerous chronic illnesses and premature death. There also appears to be a dose-response pattern in which less physical activity is related to greater health risks.
“Use it or lose it” is an apt description for the systems of the human body, and from this perspective it becomes apparent why being sedentary is bad for health. Less evident is what is happening at the chromosomal level when persons are inactive. Research indicates that this is one place where the costs of sitting are paid.
Telomeres are DNA-protein complexes that cap the ends of chromosomes. When cells divide, the telomeres are not completely replicated so that telomeres become shorter with each cell division. In other words, the shortening of telomeres is a marker for biological aging. Oxidative stress and inflammation are believed to be among the determinants of telomere shortening. Telomere shortening is associated with a number of age-related diseases, including most cancers. Persons experiencing chronic stress have been found to have shorter telomeres. And, shorter telomere length is associated with being sedentary.
Hours spent watching television, one marker used by researchers to measure sedentary behavior, has been found to be inversely related to telomere length. Studies looking at exercise and telomere length have found that physically active individuals have longer telomeres compared to inactive persons.
Physical inactivity is common in the United States. It has been estimated that approximately one-third of US adults are sitting 9 or more hours each day, and only about one-quarter of adults get the recommended amount of physical activity. Screen time is just one of the reasons why persons may be sedentary; many jobs do not require physical activity. There is a trend in which more persons are choosing to stand at work when possible, rather than sitting, but standing itself does not appear to eliminate the costs of inactivity.
There is good news for persons who sit for many hours. Evidence is accumulating that regular physical activity can reduce, and perhaps eliminate, the costs of sitting. Getting approximately 150 minutes of moderate to vigorous physical activity each weeks lessens the harms of sitting, whereas 300 minutes per week is the level at which sitting costs may be fully offset. Regular physical activity is, of course, important for all, but it is especially important for those who want to minimize the additional health costs that come with extended sitting.
Paul J. Hershberger, Ph.D.
… is a clinical health psychologist. He is Professor, Director of Research, and Director of the Division of Behavioral Health, Department of Family Medicine, Wright State University Boonshoft School of Medicine.
The URL for the e-quilibrium blog is http://blogs.wright.edu/learn/paulhershberger/
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