University at Buffalo - The State University of New York

Published: November 21, 2002

By LOIS BAKER
Contributing Editor

Being inactive is more life-threatening than being overweight or obese, results of one of the first studies to consider body weight and physical activity simultaneously and assess their independent effects on mortality has found.

For the determinedly sedentary, that's the bad news. The good news is that participants didn't need to be marathon runners to decrease their mortality risk.

Results showed that for men in this study, small amounts of physical activity were significantly protective, while moderate or intense physical activity provided little additional life-preserving benefit, irrespective of weight.

Moreover, in an interesting twist to the "leaner is better" axiom, underweight persons in this study were at greater risk of dying from any cause than people of healthy weight.

The study will be published in Annals of Epidemiology.

"Consistently, physical inactivity was a better predictor of all-cause mortality than being overweight or obese," said lead author Carlos J. Crespo, associate professor of social and preventive medicine in the School of Medicine and Biomedical Sciences.

"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," Crespo said.

The study was based on data collected for the Puerto Rico Heart Health Program. The initial data on physical activity and body measurements were collected between 1962 and 1965 from 9,824 men aged 35 to 79. Men found to have heart disease at the first examination or who died within the first three years of the study were excluded from the study to reduce any bias due to a pre-existing condition.

Researchers recontacted participants several times during the ensuing 12 years. During that follow-up period, 1,445 participants died and nine couldn't be found. The final sample for this analysis consisted of data on 9,136 men.

Participants were placed in a quartile of physical activity, based on the number of hours per day they spent at various activities. Activity hours were converted into an activity index based on METs, or metabolic equivalents, a standard method used to indicate energy expenditure. An activity index of 24 reflects no activity (one MET per hour is necessary to maintain basic bodily functions). The first activity quartile included participants with an activity index of 24 to 27; second quartile from 27 to 30; third from 30 to 37 and fourth, greater than 37.

Weight categories were based on body mass index, or BMI, which reflects a weight-to-height ratio. A BMI of 18.5 to 24.9 is considered normal or healthy. Other weight categories were underweight—BMI less than 18.5; overweight—BMI between 25 and 29.9; obese—BMI above 30.

Analyzing these variables from the 1,445 who died showed physical inactivity to be an independent risk factor for all-cause mortality. Men in activity category 1 were at twice the risk of dying than those in category 2. Additional activity provided little extra benefit, results showed.

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

However, comparing heart disease deaths based on weight category showed a 33.6 percent increase in heart disease deaths in obese (BMI=30+) men compared to men in the healthy weight category. Overweight (BMI=25-29.9) men showed only a 7 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," Crespo said.

"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."