Keep on going: busy seniors live longer, more proof that it pays to stay active.

Elderly people who bustle around the house, spend much time on their feet, climb stairs, and hold down jobs might be buying themselves precious years of life.

In a new study, researchers used a precise measure of calorie burning to assess activity. A total of 302 people, ages 70 to 82, completed questionnaires regarding their daily activities. All the volunteers got around without help, and none lived in an assisted-care facility or had been diagnosed with a life-threatening illness.

Each volunteer was given water containing a harmless, easily traced isotope of oxygen. By measuring this isotope in the carbon dioxide in each participant's urine, the researchers calculated how many calories that person burned during a 2-week period in which they went about their normal activities, says study coauthor Todd M. MANN, a physiologist at the National Institute on Aging in Bethesda, Md.

The researchers used this information to divide the volunteers into high-, medium-, and low-activity subgroups. They then kept tabs on the participants for 6 years.

Over that period, 55 of the volunteers died. Those deaths included nearly 25 percent of the people in the most sedentary group, 18 percent of the medium-activity group, and 12 percent of the most active group, the researchers report in the July 12 Journal of the American-Medical Association. When the researchers took into account each person's base metabolic rate and other factors such as weight, age, gender, race, and smoking status, the correlation between greater activity and survival was even stronger.

Every additional 287 calories burned per day lowered a person's risk of death by one-third, Manini says. By comparison, a 155-pound person walking 3 miles in an hour burns about 250 calories.

"There's a difference between small activities and inactivity," Manini says. "Any movement is better than no movement."

"This is the first study that uses objective measures of activity related to energy expenditure to show that more-active older adults have lower mortality rates," says physiologist Gary R. Hunter of the University of Alabama at Birmingham.

The people burning the most calories weren't necessarily maintaining scheduled exercise or walking regimens. Such routines were equally distributed across the three subgroups.

Rather, the most active people found other ways to stay mobile. For example, they were more likely than the others to have paying jobs and to climb steps regularly.

"This gives us one more very compelling argument for maintaining high levels of physical activity across the life span," Hunter concludes.