Sit Less, Live Longer?
If people need motivation to get up from their office chairs or couches and become less sedentary, two useful new studies could provide the impetus. One found that sitting less can slow the aging process within cells, and the other helpfully underscores that standing up — even if you are standing still — can be good for you as well.
For most of us nowadays, sitting is our most common waking activity, with many of us sitting for eight hours or more every day. Even people who exercise for an hour or so tend to spend most of the remaining hours of the day in a chair.
The health consequences of this sedentariness are well-documented. Past studies have found that the more hours that people spend sitting, the more likely they are to develop diabetes, heart disease and other conditions, and potentially to die prematurely — even if they exercise regularly.
But most of these studies were associational, meaning that they found a link between sitting and illness, but could not prove whether or how sitting actually causes ill health.
So for the most groundbreaking of the new studies, which was published this month in the British Journal of Sports Medicine, scientists in Sweden decided to mount an actual experiment, in which they would alter the amount of time that people spent exercising and sitting, and track certain physiological results. In particular, with this experiment, the scientists were interested in whether changes in sedentary time would affect people’s telomeres.
If you are unfamiliar with the componentry of your genes, telomeres are the tiny caps on the ends of DNA strands. They shorten and fray as a cell ages, although the process is not strictly chronological. Obesity, illness and other conditions can accelerate the shortening, causing cells to age prematurely, while some evidence suggests that healthy lifestyles may preserve telomere length, delaying cell aging.
For the new experiment, the Swedish scientists recruited a group of sedentary, overweight men and women, all aged 68, and drew blood, in order to measure the length of telomeres in the volunteers’ white blood cells. Then half of the volunteers began an individualized, moderate exercise program, designed to improve their general health. They also were advised to sit less.
The other volunteers were told to continue with their normal lives, although the scientists urged them to try to lose weight and be healthy, without offering any specific methods.
After six months, the volunteers all returned for a second blood draw and to complete questionnaires about their daily activities. These showed that those in the exercise group were, not surprisingly, exercising more than they had been previously. But they were also, for the most part, sitting substantially less than before.
And when the scientists compared telomeres, they found that the telomeres in the volunteers who were sitting the least had lengthened. Their cells seemed to be growing physiologically younger.
Meanwhile, in the control group telomeres generally were shorter than they had been six months before.
But perhaps most interesting, there was little correlation between exercise and telomere length. In fact, the volunteers in the exercise group who had worked out the most during the past six months tended now to have slightly less lengthening and even some shortening, compared to those who had exercised less but stood up more.
Reducing sedentary time had lengthened telomeres, the scientists concluded, while exercising had played little role.
Exactly what the volunteers did in lieu of sitting is impossible to say with precision, said Per Sjögren, a professor of public health at Uppsala University in Sweden, who led the study, because the researchers did not track their volunteers’ movement patterns with monitors. But “it’s most likely,” he said, that “sitting time was predominantly replaced with low-intensity activities,” and in particular with time spent standing up.
Which makes the second new study of sedentary behavior particularly relevant. Standing is not, after all, physically demanding for most people, and some scientists have questioned whether merely standing up — without also moving about and walking — is sufficiently healthy or if standing merely replaces one type of sedentariness with another.
If so, standing could be expected to increase health problems and premature death, as sitting has been shown to do.
To find out whether that situation held true, Peter Katzmarzyk, a professor of public health at the Pennington Biomedical Research Center in Baton Rouge, La., and an expert on sedentary behavior, turned to a large database of self-reported information about physical activity among Canadian adults. He noted the amount of time that the men and women had reported standing on most days over the course of a decade or more and crosschecked that data with death records, to see whether people who stood more died younger.
The results, published in May in Medicine & Science in Sports & Exercise, are soothing if predictable. Dr. Katzmarzyk found no link between standing and premature death. Rather, as he writes in the study, “mortality rates declined at higher levels of standing,” suggesting that standing is not sedentary or hazardous, a conclusion with which our telomeres would likely concur.
This blog was originally published in the New York Times.