Live slow die young
Sedentary lifestyles could make you old before your time.
Active people could be up to 10 years 'younger' than couch potatoes, at least according to one measure of biological age.
Tim Spector, director of the Twin Research Unit at St Thomas’ Hospital in London, looked at the levels of physical activity of 2,401 twins and assessed the length of their telomeres - the 'caps' on the ends of their chromosomes that help to protect the DNA from wearing down during the replication process that replenishes cells. Telomeres shorten over an individual’s lifetime and are thought to function as a marker for ageing. Smokers and obese people were already known to have shorter telomeres than their healthier counterparts.
The team found that, on average, telomeres in the most active group (who took more than 3 hours 20 minutes of exercise a week) were 200 nucleotides longer than that of the least active group (who took less than 16 minutes exercise a week).
“This difference suggests that inactive subjects may be biologically older by 10 years compared with more active subjects,” say Spector and colleagues in their paper in Archives of Internal Medicine1.
Exercise is good for you
The researchers also looked at matched pairs of twins and found an average difference of 88 nucleotides between the more and less active siblings.
The group cannot be certain from this that activity levels are having a direct impact on telomere length. “We can’t prove that," admits Spector. But they think it is the most likely explanation; the researchers corrected their statistics for the impact of smoking, obesity, social status and a whole host of other possible confounding factors. "It’s very hard to think of anything else that would be a confounder that we haven’t measured,” he says.
If inactivity is to blame, Spector can think of a couple of ways in which it might work. It is known that the faster cells are replenished, the faster telomeres shrink, and it's possible that physically inactive people are for some reason experiencing a high cell turnover. Another possible explanation lies in oxidative stress — in which more reactive oxygen atoms or oxygen molecules are created and stress the cells. “It’s possible we need exercise to damp down oxidative stress,” says Spector. Alternatively, it could be that a little bit of oxidative stress is caused by exercise, but that this little bit of harm does some good to our cells.
In an editorial alongside Spector’s paper, Jack Guralnick, chief of the Epidemiology and Demography Section at the National Institute on Aging in the United States, says more work is needed to pin down whether there is a causal link2.
“It’s a provocative finding,” he says. “The statistical association is there; it’s quite clear in the work.” But other diseases that weren’t corrected for could be causing the association, he says. “Proving causality in this kind of study is nearly impossible,” says Guralnick.
Spector admits that his findings will excite debate in researchers who study ageing; the idea that telomere length is directly related to ageing isn't fully accepted. “There’s still controversy,” he says. “When I write that in papers you get one in three reviewers being angry about it.”
Whether or not the results of Spector’s team are confirmed by future work, researchers say they are likely to trigger an increase in research in this area. “This is kind of an opening salvo,” says Guralnik.
- Cherkas, L., et al. Arch. Intern. Med., 168, 154-158 (2008).
- Guralnik, J. Arch. Intern. Med., 168, 131-132 (2008).