Honolulu: Keeping fit inmiddle age can add an extra ten years to your lifespan, say scientists.

In one of the largest studies ever carried out, they conclude that far from being down to luck, health and habits at middle age determine your chances of hitting 85.

Those who keep fit, avoid smoking, drinking too much and are free of common diseases in their 50s have three times the chance of reaching their 80s in good health than those with bad habits.

Experts in the US study, which is published in the Journal of the American Medical Association, say the key rules for living longer are: eating healthily; staying slim; monitoring blood pressure and cholesterol; exercise; keeping your brain active; and getting married.

The conclusions come from a study of 6,000 men aged 54 over 40 years, repeatedly testing them for six major diseases as well as mental and physical impairment.

Almost 2,500 lived to 85. And more than one in 10 was still free of disease, physically able to walk half a mile with ease and showed no sign of mental decline.

It also found that the biggest things these survivors had in common was their behaviour in middle age.

In fact, the research by the Pacific Health Research Institute and Kuakini Medical Center in Hawaii concluded that men in their 50s who were completely healthy and had no bad habits had a 55 per cent chance of reaching 85 with no major problems.

However, those who had at least six risk factors in their 50s such as smoking, eating an unhealthy diet, being overweight, drinking too much, high blood pressure or cholesterol only had a nine per cent chance of getting to that age in a healthy state.

Dr Bradley Willcox who led t he study said: “These men provide an important window for understanding what is realistically possible for healthy ageing in men.”

“Measures from this study, such as grip strength, suggest that it is important to be physically robust in midlife, ” he wrote. “This is consistent with theories of ageing that suggest that better-built organisms last longer and that physiological reserve is an important determinant of survival.

“In summary, we have identified several potentially important risk factors for healthy survival in a large group of middle-aged men. These risk factors can be easily measured in clinical settings and are, for the most part, modifiable.

“This study suggests that common approaches that target multiple risk factors simultaneously, such as avoidance of smoking or hypertension, and approaches that enhance insulin sensitivity, such as maintaining a lean body weight, may improve the probability of better health at older ages.” It had been thought that living longer was largely down to having “good genes” or simply being lucky.

But this latest study proves that although some diseases such as cancer cannot be avoided, most of the major risk factors, including heart disease, lung disorders and some blood glucose disorders, can be prevented simply by eating a good diet, avoiding cigarettes and taking exercise.

The study does not find that abstinence is a key to long life. Men who lived to 85 still enjoyed up to three alcoholic drinks a day.