BioEd Online

Regular exercise keeps us fit. But not everyone is born equal: a few people get little benefit from physical activity because their genetic makeup doesn't allow it.

Research now shows that the same holds true for the elderly, where the stakes are much higher.

A third of adults over 70 in the US are unable to walk for half a kilometre without difficulty, or to climb up ten steps without having to stop for a rest. Such people are four times more likely to end up in a nursing home, and three times likelier to die before those who are fitter.

To find out if there is a genetic component in who stays fittest the longest, Stephen Kritchevsky at Wake Forest University in Winston-Salem, North Carolina and his colleagues conducted a four-year study of 3,000 American adults in their seventies. The team examined participants every six months, and asked them about their mobility and how much exercise they took.

At the end, they were surprised by how big a role genetics appears to play in keeping the elderly on their feet.

Hearty effort

A third of the group reported that they were 'active', burning more than 1,000 calories per week during exercise - the equivalent of walking for about five or six hours. And 40% of the study group developed some sort of mobility problem during the four years.

The researchers focussed on a gene for an enzyme called angiotensin-converting enzyme (ACE), which is important in heart strength and regulating blood pressure.

There are two types of ACE gene. The slightly shorter one, called D for deletion, results in the synthesis of higher levels of the enzyme than its longer counterpart, I, or insertion. Studies have shown that among athletes, those with two copies of the 'D' form excel in sports that rely on strength and power. While those with two copies of the 'I' form tend to be better at endurance sports.

"We really didn't know whether the 'D' or the 'I' form would be most important in elderly people," says Kritchevsky. In the end, those with two 'D' genes - about a third of the overall group - were most likely to retain their mobility. Perhaps they had extra strength that protected them from injury, the team speculates.

At the other end of the scale, those with two copies of the 'I' gene were 45% more likely to develop difficulties than those with at least one 'D' gene, regardless of how much they exercised. The results are reported in the Journal of the American Medical Association¹.

This doesn't mean that senior citizens with two 'I' genes might as well become couch potatoes, say the researchers. Those who exercised regularly were still less likely to develop mobility problems, regardless of their genetics. Even if those with two 'I' genes can't benefit from exercise as much as their comrades with more favourable gene profiles, they are still better off for a brisk walk.