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 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. But most of these studies could not prove whether or how sitting actually causes ill health.
So for the most groundbreaking of the new studies, published in the British Journal of Sports Medicine, scientists in Sweden decided to mount an actual experiment for it. In particular the scientists were interested in whether changes in sedentary time would affect people?s telomeres ? the tiny caps on the ends of DNA strands.
Telomeres 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.
For the new experiment, the Swedish scientists recruited a group of sedentary, overweight volunteers, all aged 68, and drew blood to measure the length of telomeres. Then half of the volunteers began an individualised, moderate exercise programme, 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.
After six months, the volunteers all returned for a second blood draw. This showed that those in the exercise group were exercising more than they had been previously. But they were also sitting substantially less than before.
And the scientists also found that 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.
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.
Exactly what the volunteers did in lieu of sitting is impossible to say with precision, said Per Sj?gren, a professor of public health at Uppsala University in Sweden, who led the study. 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.
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.
If so, standing could be expected to increase health problems and premature death, as sitting has been shown to do.
To find out, Peter Katzmarzyk, a professor of public health at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, and an expert on sedentary behaviour, 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.
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.
– Gretchen Reynolds