Poor physical fitness is a better predictor of death than a host of other documented and widely feared health risk factors, including smoking, hypertension and heart disease, according to new research published this month in the New England Journal of Medicine.

The role of exercise in improving survival held true for every elevated-risk group studied, from those who had had heart attacks to those with chronic emphysema and other lung diseases. In every case the risk of death in the fittest patients was about half that of the least fit, reports The Washington Post.

'No matter how we twisted it, exercise came out on top,' said lead author Jonathan Myers, a researcher at Veterans Affairs Palo Alto Health Care System and professor of medicine at Standford University.

While the fittest patients had the lowest risk of death regardless of underlying condition, the biggest gain in the protective benefit of exercise occurred at the other end of the spectrum.

When the least fit subjects stepped up their physical activity, their relative risk of death dropped by a higher proportion than any other groups.