Being inactive is more life threatening than being overweight or obese, according to researchers at the University of Buffalo in New York.

The researchers conducted one of the first studies to consider body weight and physical activity together, and assess their independent effects on the rate of death.

For men in the study, small amounts of physical activity were significantly protective, while moderate or intense physical activity gave little additional lifesaving benefit, regardless of the person's weight.

Also, underweight participants in the study were at greater risk of dying from any cause than people of healthy weight, according to the research published in the Annals of Epidemiology.

"Consistently, physical inactivity was a better predictor of all-cause mortality than being overweight or obese," said Carlos J. Crespo, Dr.P.H., associate professor of social and preventive medicine and lead author of the study.

"Our findings confirm that, independent of other known risk factors, such as hypertension, high cholesterol and smoking, physical activity exerts positive health benefits independent of body weight. The benefit may derive from the fact that regular moderate physical activity, no matter how much you weigh, appears to stimulate the immune system, improve insulin sensitivity and increase bone density, among other positive effects. These findings send a strong message that everyone should strive to be active in some way," said Crespo.

Researchers assessed data from the Puerto Rico Heart Health Program, designed to examine sickness and death from coronary heart disease in rural and urban men. The sample for this study consisted of data on 9,136 men.

Participants were placed in one of four groups of physical activity, based on the number of hours per day they spent at various activities. The activity hours were converted into an activity index based on metabolic equivalents. The first activity group included participants with an activity index of 24 to 27, the second group had an index of 27 to 30, the third group had an index of 30 to 37 and the fourth group had an index greater than 37.

Physical inactivity was shown to be an independent risk factor for all-cause mortality. Men in the first (lowest) activity group were at twice the risk of dying of those in the second group. Additional activity provided little extra benefit.

When deaths from heart disease were considered separately, findings showed sedentary men had 38 percent more deaths from the heart disease than men in the next activity group. Men in the highest activity group lived the longest, regardless of their weight.

However, comparing heart disease deaths based on weight showed a 33.6 percent increase in heart disease deaths in obese men compared to men at a healthy weight. Overweight men showed only a seven percent increase in deaths from heart disease.

"These findings are of public health significance because both physical inactivity and obesity have been cited by the Surgeon General as two of the top 10 public-health priorities for the nation," said Crespo. "In this study, inactivity was a significant predictor of all-cause mortality, and overweight men who exercised reduced their risk of premature death compared with overweight men who did not exercise."

"We encourage individuals not to evaluate their exercise program on pounds of body weight lost, but to engage in a regular exercise program for their general health," continued Crespo. "Exercise is good for all persons, regardless of their body weight."

Other sources: University of Buffalo