Elderly women who sit for more than 10 hours a day with low physical activity have cells that are biologically older by eight years compared to women who are less sedentary, University California San Diego School of Medicine researchers report.
The study found that elderly women with less than 40 minutes of moderate-to-vigorous physical activity per day and who remain sedentary for more than 10 hours per day have shorter telomeres. Tiny caps found on the ends of DNA strands, like the plastic tips of shoelaces, telomeres protect chromosomes from deterioration and progressively shorten with age.
As a cell ages, it’s telomeres naturally shorten and fray, but health and lifestyle factors, such as obesity and smoking, may accelerate that process. Shortened telomeres are associated with cardiovascular disease, diabetes and major cancers.
Sedentary Lifestyle And Telomeres
Aladdin Shadyab, PhD, lead author of the study with the Department of Family Medicine and Public Health at UC San Diego School of Medicine, said:
“Our study found cells age faster with a sedentary lifestyle. Chronological age doesn’t always match biological age."
Shadyab and his research team believe they are the first to objectively measure how the combination of sedentary time and exercise can impact the aging biomarker.
Nearly 1,500 women, ages 64 to 95, participated in the study. The women are part of the larger Women’s Health Initiative, a national, longitudinal study investigating the determinants of chronic diseases in postmenopausal women.
The participants completed questionnaires and wore an accelerometer on their right hip for seven consecutive days during waking and sleeping hours to track their movements.
“We found that women who sat longer did not have shorter telomere length if they exercised for at least 30 minutes a day, the national recommended guideline,” said Shadyab. “Discussions about the benefits of exercise should start when we are young, and physical activity should continue to be part of our daily lives as we get older, even at 80 years old."
Cross-sectional Study
This cross-sectional study used data from women taking part in the Women’s Health Initiative. Cross-sectional studies can find correlations between different factors – in this case, sitting time and telomere length.
But because this type of study only looks at one point in time, researchers can’t say which factor happened first, so it’s not very useful for telling us whether one causes the other.
It’s not news to anyone that being more physically active and spending less time sitting around is likely to keep people in better health. But this study has many limitations that make it difficult for us to rely on its results.
While they are used as a marker for ageing cells, telomeres are not a direct measure of ageing. Although shortened telomeres have been linked to certain diseases, everyone’s telomeres shorten over time.
Saying shorter telomeres make someone “biologically older” doesn’t mean much. This hasn’t stopped the emergence of private companies offering to measure your telomeres – but it’s unclear what exactly you could usefully do with that information.
And the only cells studied in this research were blood cells, so we don’t know whether the results would have held for brain cells, muscle cells or any other cells in the body.
Physical Activity
Doctors have tried to disentangle the effects of physical activity from the effects of being sedentary before without much success. Generally, as in this study, research seems to show that if you get plenty of moderate to vigorous physical exercise, the amount of time you spend sitting or lying down doesn’t make much difference.
The researchers carried out a lot of comparisons and used multiple models to try to show sedentary time was linked to telomere length. In most of these models, once you take account of women’s age, ethnicity, body mass index and long-term illnesses, there was no link.
Only when the researchers stratified the results by how much physical activity women did could they show a link in one category: those who did the least physical activity.
That suggests sedentary behavior is not the strongest factor to affect telomere length.
Another problem with the study is it only looked at telomere length and physical activity at one point in the women’s lives. We don’t know how much physical activity they’d done throughout their lives, or whether their telomeres had shortened faster than other women recently or at an earlier stage in life.
The study doesn’t add much to what we already know: physical activity is likely to be beneficial for people at all stages of life, and everyone should aim to get at least the recommended level of 30 minutes of moderate to vigorous physical activity a day.
The research was supported by the National Heart, Lung, and Blood Institute, and the National Institute of Arthritis and Musculoskeletal and Skin Diseases.
Aladdin H. Shadyab et al.
Associations of Accelerometer-Measured and Self-Reported Sedentary Time With Leukocyte Telomere Length in Older Women
American Journal of Epidemiology, January 2017 DOI: 10.1093/aje/kww196