Fitness is more important than thinness in retaining mobility, strength and balance in old age.

Middle-aged people who do half an hour’s vigorous activity three times a week are half as likely as the sedentary to suffer physical decline and impaired mobility as they get older.

“Use it or lose it” was the message, said Dr Iain Lang, of the Peninsula Medical School in Plymouth, who, with collaborators in the United States, studied data on more than 10,000 people aged between 50 and 69 for up to six years.

Importantly, he said, the benefit of exercise was enjoyed regardless of body mass index. All groups roughly halved their risks of physical decline by doing exercise — so that a fit obese person did as well, or better, than a thin, unfit one.

“Some people take up exercise and then give up when they don’t lose weight,” Dr Lang said. “This research shows that you get important benefits from exercise even if it doesn’t help you lose weight.”

The research was carried out using data from two ongoing studies, the English Longitudinal Study of Ageing and the US Health and Retirement Study. Both are long-term studies of the changes that take place as middle-aged people move into old age.

Both groups — 8,692 in the US, and 1,507 in England — were asked at the start if they did any vigorous exercise. This could include sports, heavy housework, mowing the lawn, sweeping up leaves, or any job that involves physical labour and would make a participant feel out of breath or sweaty.

The team worked out from the answers how many of the participants did at least 30 minutes of this type of exercise at least three times a week. They then compared this with the experience of physical decline in the participants.

They conclude in the Journal of the American Geriatrics Society that those who maintained a reasonable level of physical activity were more likely to be able to walk distances, climb stairs, maintain their sense of balance, stand from a seated position with their arms folded, or sustain their hand grip as they got older.

Across all weight ranges, the rate of decreased physical ability later in life was twice as high among those who were less physically active. Being overweight or obese was linked with an increase in disability, but much of that increased risk could have been eliminated by keeping fit.

As examples, 21.1 per cent of English people of normal body mass index (20-24.9) became physically impaired over the course of the study if they did no exercise; only 12.4 per cent of them did if they were active.

Among the obese (BMI 30 or over), 31.6 per cent of the English participants became physically impaired if they did no exercise, while only 15.4 per cent of the active ones did.

Indeed, being physically active almost eliminated the difference in deterioration otherwise noticed between the obese and those of normal weight. The American data showed similar, if less striking, results.

“There are three truly interesting results from this research,” Dr Lang said. “The first is that our findings were similar from the US and the UK, which suggests that they are universal. The second is that exercise in middle age does not just benefit people in terms of weight loss — it also helps them to remain physically healthy and active later in life. And the third is that, in terms of results from activity, weight does not seem to be an issue.”

Body of evidence

— Being overweight or obese increases the risks of heart disease, diabetes, high blood pressure, stroke and some cancers

— Whether too much weight kills people any sooner seems to depend on fitness levels

— One US study followed 25,000 men for more than a decade and found that an obese man was 1.7 times more likely to die than one of normal weight. But men who were fit and fat hardly increased their risks at all; an unfit man of normal BMI was twice as likely to die as a fit obese man

— How fit do you need to be? Any exercise is better than none, but in this study the men were regularly active – doing sport or heavy work

— The new study sets a similar target; to get the benefit you need to raise a sweat. But you do not have to be an athlete. A brisk uphill walk three times a week is enough

Bullying, obesity and depression among children are on the rise due to increasingly sophisticated advertising tactics targeting the young, according to a report to be published today by the National Union of Teachers. It warns that children need to be protected against commercial exploitation by companies that routinely hire child psychologists to help them tomaximise the impact of adverts.

The report said that children were bombarded with unrealistic and unachievable images of what they should look like, leading to a rise in anorexia, bulimia and other eating disorders.

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