May 19, 2010, 12:01 am
Phys Ed: Do Our Genes Influence Our Desire to Exercise?
By GRETCHEN REYNOLDS
Nick Dolding/Getty Images
Is the urge to exercise bred in our bones? That’s the intriguing question that European researchers recently set out to examine by looking at the activity habits of 37,051 sets of twins. Twins are popular with geneticists, because they provide a neat statistical model for determining whether a behavior is influenced by genetics or exclusively by environment. Identical twins share 100 percent of their genome, fraternal twins share 50 percent. All twin pairs, if raised together, share approximately the same early environment. So if a behavior is more common between identical twins than between fraternal twins, it is presumably being directed to some degree by genes.
In the study, scientists looked at the decision to exercise or not. They turned to survey data covering twin pairs ages 19 to 40 in Australia, Denmark, Finland, the Netherlands, Norway, Sweden and the United Kingdom. Although the researchers set a very loose standard of one hour per week of light jogging or an equivalent activity to classify someone as an ‘‘exerciser,’’ only about 44 percent of the males and 35 percent of the females met the standard. Across the board, however, the identical-twin pairs were more likely to share an exercise pattern than the fraternal twins.
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Using complicated statistical formulas, the scientists concluded that differences in exercise behavior were about 60 percent attributable to genes. In other words, your parents influence your decision about whether to be active, not just by signing you up for soccer camp when you’re a kid but also by bequeathing you a genetic urge to work out — or not.
The study’s results, published in 2006 by the Public Library of Science, were eye-opening. ‘‘Most people probably hadn’t thought of exercise behavior as a domain in which genetics would be involved,’’ says Tuomo Rankinen, an associate professor with the Human Genomics Laboratory at the Pennington Biomedical Research Center in Baton Rouge, La., and expert on exercise genetics.
More recent studies have reinforced the idea, most persuasively a report published last year in the journal Medicine and Science in Sports and Exercise that looked at the actual genomes of exercisers and the exercise-averse. Using blood samples from more than 2,600 people, researchers examined more than a million and a half sites along each person’s DNA. They found that people who were active (but not necessarily athletic) tended to have similar variations of several different genes. The genes in question didn’t affect obvious physical characteristics, like speed and strength. Instead, the genetic differences were subtle. One of the affected genes is thought to influence how people respond to fatigue, suggesting that, for some people, the same amount of exercise may be more tiring — and less appealing — than for others, even if they are equally fit. Another gene is widely expressed in both muscles and the brain and is likely to have an impact on how physically easy and mentally rewarding exercise feels. Yet another gene has been linked to how well the body regulates energy, which can have an effect on the desire to exercise.
‘‘It was so interesting’’ to find these differences, says Hong-Wen Deng, a professor of orthopedic surgery at the school of medicine of the University of Missouri in Kansas City, Mo., and one of the study’s leaders. He and his colleagues are planning to expand the study to a much larger group of volunteers soon and expect to find many more genes that might be involved in exercise behavior.
Learning more about the genetics of active people is important, Mr. Rankinen says, because it may allow for interventions to goose everyone else. ‘‘Right now, most people don’t exercise, even though we all know that, for health reasons, we should,’’ Mr. Rankinen says. Maybe, through our knowledge of genetics, ‘‘we can find ways to help make exercise easier or more attractive for people.’’ If, for instance, it turns out that some people have a genetic predisposition to develop especially sore muscles after running, he says, ‘‘maybe we could start directing those people to other kinds of exercise.’’
No matter how much is learned about the genetics of activity, though, the work will never provide carte blanche for physical lassitude. No blaming your DNA if you decide to skip a workout. ‘‘Even at the highest percentages of likely heritability’’ of exercise behavior, Mr. Rankinen says, the choice to exercise is yours.
http://well.blogs.nytimes.com/2010/05/19/phys-ed-do-our-genes-influence-our-desire-to-exercise/
