You don't have to climb Kilimanjaro on your 70th birthday or run an Ironman on your 75th. You don't even have to power walk around the neighborhood three times a week to live longer.
For septuagenarians and those older, just puttering around, doing simple chores or expending energy in any way may influence survival, according to a new study.
"The message here is that any movement is better than no movement for older adults," said Todd M. Manini, a researcher from the National Institute on Aging and lead author of the study, published Wednesday in the Journal of the American Medical Assn. "It doesn't necessarily have to come from structured exercise activity, like going to a gym."
If documented by future research, "the findings would have major implications for physical activity recommendations for older adults," said Steven N. Blair, president and chief executive of the Cooper Institute in Dallas, and William Haskell of the Stanford University School of Medicine, in an accompanying JAMA editorial.
Previous research has reported that a sedentary lifestyle increases the risk of chronic disease and shortens life, but researchers say that those earlier studies used estimations, based almost entirely on the subjects' recollections, of how much energy they were expending.
This study, however, follows subjects over time and includes an objective measure of their physical activity using a biochemical test.
To conduct the study, researchers followed 302 mobile, healthy and independently living adults 70 to 82 years old. They were tracked from 1997 or 1998 to 2006.
At the beginning of the study, researchers measured the subjects' energy expenditure over a two-week period using a technique known as the doubly labeled water method to accurately assess how much energy they burned. (In this method, subjects drink a special water made up of nonradioactive isotopes. Then scientists test the urine for the rate at which the isotopes are eliminated from the body as carbon dioxide.)
To determine the amount that subjects expended in activities, the researchers measured participants' resting metabolic rate (how much energy a body uses just to survive) and subtracted that from their total energy use. Participants also filled out a standard physical-activity questionnaire, which asked how much walking, high-intensity exercise and activities (such as care-giving and stair-climbing) they did over that two-week period.
The results were surprising: The people who used the most energy did not perform any more high-intensity exercise or walking exercise than those who used the least. Instead, the scientists found, those who burned the most energy were more likely to work for pay and to climb more stairs each day.
Fifty-five participants (18.2%) died over the study's eight-year period. After adjusting for various factors, the researchers found that higher levels of activity -- whether from low-intensity everyday tasks or high-intensity exercise -- were associated with living longer.
When they divided the participants into three groups by energy expenditure, they found that those in the high energy expenditure group had a 12.1% risk of dying during the course of the study, while those in the lowest energy expenditure group had a 24.7% risk. After adjusting for lifestyle differences, such as smoking, the scientists calculated that those who were most active had a 69% lower risk of death than those who were least active.
But questions remain, researchers said. It is possible, for example, that the method to assess daily activities wasn't entirely accurate, relying as it did to some extent on subjects' recollections. Also, just because subjects performed a certain number of activities during one two-week period does not mean that they continued to do those same activities for the next six to eight years, or until they died.
But some researchers were impressed by how little activity it may take to affect longevity.
"It looks like the group that had the highest level of activity only [did] about 1.3 hours per day," said Dr. Gary Small, director of UCLA's Center on Aging. "One message here is that you don't have to dig ditches eight hours a day. A reasonable amount of activity is protective."
But the researchers cautioned that what works well for older people may not work for children or younger adults.
"I would not want parents or children to be fooled into thinking that just regular, very, very low-intensity activity is going to help kids be healthy," said Michael F. Bergeron, an applied physiologist and professor at the Medical College of Georgia and a member of the American College of Sports Medicine. "They need exercise, and they need it at a certain intensity and duration."
If younger adults want to enhance their health, he added, they have to "get those numbers up there" to increase their heart rate and energy expenditure and get their blood flowing.
Manini said his research is "another piece of the puzzle" of how exercise improves health and longevity and how little exercise it may take to do so.
"We thought before that that was due to high-intensity and moderate-intensity exercise," he said. "But this is a little different. This is suggesting that just higher energy use through the day is associated with lower mortality."
As for why this is true, so far no one knows.
"The biological mechanisms for this are really unknown," Manini said. "It sets up a whole new line of research."