Seniors who burn the most calories live longer

By Anne Harding

NEW YORK (Reuters Health) - Among a group of older people followed for about six years, those who expended the most energy in their daily activities were less likely to die than less-active individuals, a new study shows.

"The public health message is that higher energy use is associated with lower risk of death in older adults, and that this could be really appealing for many older adults who are intimidated by exercise," Dr. Todd M. Manini of the National Institute on Aging in Bethesda, Maryland, the study's lead author, told Reuters Health.

"Any movement is really better than no movement, that's the real message for older adults," said Manini.

While past research has linked higher activity levels to reduced mortality risk, such studies have relied on participants' own reports of their activities, which are frequently inaccurate, the researchers point out in their report in the July 12 issue of the Journal of the American Medical Association.

To get a clearer picture of how active people really were, Manini and his team used a technique called the doubly labeled water method, which determines how many calories a person burns over a two-week period by measuring the amount of carbon dioxide they produce. "It is considered the gold standard measure of activity thermogenesis or activity energy use in a person's normal environment," Manini said.

The study included 302 men and women aged 70-82, all of whom were high-functioning -- meaning they could walk at least a quarter-mile on their own -- and living independently. Manini and his colleagues subtracted the amount of calories people burned at rest from their total energy expenditure to determine the amount of energy they used during activity.

The team classified the subjects based on energy expenditure -- high, middle or low.

Fifty-five of the study participants, or 18.2 percent, died during an average follow-up of a little more than six years. The mortality rate was 12.1 percent for the group of most active study participants, compared to 24.7 percent for the least active group.

Manini said the difference doesn't appear to have been due to less active people being sicker than the most active individuals. None of the study participants had any terminal illness, and there was no difference in the number of diseases or types of diseases between the most active group and the least active group, he explained.

People in the high-energy expenditure group were more likely to report working for pay, and they climbed two flights of stairs more each day than those in the lowest-energy expenditure group. However, there was no difference among the three groups in the amount of structured activity they reported, such as walking or high intensity exercise.

This suggests, Manini said, that energy expenditure from everyday activities like gardening, grocery shopping and washing dishes was largely responsible for the survival benefits.

In an accompanying editorial, Drs. Steven N. Blair of the Cooper Institute in Dallas, Texas, and William L. Haskell of the Stanford University School of Medicine, California, note that this study is the first to look at the association between mortality and objectively measured physical activity, and call the findings "striking."

About 30 percent of the energy expended by the most active people in the study was likely due to self-reported physical activity, they point out, while the rest came from non-exercise activities like standing, moving around the room and "fidgeting."

More research will be needed, Blair and Haskell conclude, to estimate the optimum intensity and amount of physical activity to boost health and reduce mortality.

SOURCE: Journal of the American Medical Association, July 12, 2006.