Activity Found to Spur Prolonged Life

BETHESDA, Md., July 11 -- Expending energy by walking, climbing stairs, doing household chores, or even washing windows may enhance survival in healthy older adults, according to investigators here.

Compared with individuals with the lowest activity level, those at the highest level had a 69% lower risk of all-cause death, Todd Manini, Ph.D., of the National Institute on Aging here, and colleagues, reported in the July 12 issue of the Journal of the American Medical Association.

The researchers studied the energy expenditure during free-living activity in 302 high-functioning, biracial, community-dwelling older adults (ages 70 to 82; 150 men, 152 women). Fifty-five participants (18.2%) died during follow-up.

An important strength of this study, Dr. Manini wrote, was the accurate and precise method of determining energy expenditure. Earlier studies have used questionnaire assessments, which were subject to recall bias, he said.

In this study, the participants' total energy expenditure over two weeks was assessed with an accurate and precise method using doubly labeled water (water labeled with the stable isotopes of ²H, eliminated as water, and ¹⁸O, eliminated as water and carbon dioxide).

Resting metabolic rate was measured by indirect calorimetry, and the thermic effect of meals was estimated at 10% of the total energy expenditure, the researchers said.

Participants were divided into three energy tertiles (low, < 521 kcal/d; middle, 521 to 770 kcal/d; and high, >770 kcal/d) and were followed for a mean of 6.15 years from 1998 to 2006.

As a continuing risk factor, a mean (SD) increase in free-living activity energy expenditure (287 kcal/d) was associated with a 32% lower risk of all-cause mortality after adjusting for age, sex, race, study site, weight, height, percentage of body fat, and sleep duration (hazard ratio, 0.68; 95% CI, 0.48-0.96).

Using the same adjustments, individuals in the highest tertile of free-living activity energy expenditure were at a significantly lower mortality risk, compared with the lowest tertile (hazard ratio, 0.31; CI, 0.14-0.69).

The absolute risk of mortality was 12.1% in the highest tertile of energy expenditure, 17.6% in the middle, and 24.7% in the lowest tertile, the researchers reported. Absolute risks were similar to these for tertiles of physical activity level, the researchers reported.

The effect of free-living activity energy expenditure changed little after further adjustment for self-rated health, education, prevalent health conditions, and smoking behavior, they added.

According to self-reports, individuals expending higher levels of free-living activity energy were more likely to work for pay (P=.004) and climb stairs (P=.01). However, self-reported high-intensity exercise, walking for exercise, walking other than for exercise, volunteering, and care-giving did not differ significantly across the energy tertiles. This lack of relationship is likely due to inaccuracies in self-reported activity levels, the investigators said.

Turning to well-established metabolic equivalent values for physical activity, the researchers said that for every 287 kcal/d in free-living energy expenditure there is an approximately 30% lower risk of mortality. Further estimation found that individuals who performed 75 minutes of activity a day would expend 287 kcal/d.

Activities that meet this metabolic equivalent include household chores (vacuuming, mopping the floor, washing windows, etc.), child/adult care, walking at a pace of 2.5 mph, and non-sitting work, or volunteering. Most important, they said, this accumulation is from usual daily activities that expend energy and not necessarily from volitional exercise.

One limitation of observational studies of physical activity, the investigators wrote, is that unhealthy individuals are less likely to be active. In the current study, they noted, the recruited individuals were high-functioning adults who did not have mobility disabilities.

This study found no benefits of energy expenditure in the moderate range, suggesting that further work is needed to establish appropriate categories of physical activity levels that are suitable for older adults. Furthermore, the investigators said, the relatively small sample size limited the ability to assess cause-specific mortality.

Because the doubly labeled water method directly measures carbon dioxide production over an extended period, it is considered the most accurate estimate of free-living energy expenditure.

However, it is expensive, Dr. Manini said, and requires special expertise. Nonetheless, he said, the strong protective effects observed in this study demonstrated a more accurate measurement in a substantially reduced sample size compared with that needed for a simply performed but less precise questionnaire assessment.

In conclusion, Dr. Manini noted that previous self-reported measurements may have underestimated the benefits of higher levels of physical activity in older adults. "Efforts to increase or maintain free-living activity energy expenditure will likely improve the health of older adults."

In an accompanying editorial, Steven Blair, P.E.D., of the Cooper Institute in Dallas, and William Haskell, Ph.D., of Stanford, wrote that a major contribution of this study is the use of a quantitative measurement of energy expenditure. "Higher levels of activity energy expenditure appear to be protective, and it is relevant to discuss how much and what type of physical activity is required to achieve these benefits," they wrote. "Ultimately public health experts should consider how these results can be translated into recommendations for individuals."

But because the physical activity technique does not provide information about the intensity profile of energy expenditure during activity, nor could the physical-activity questionnaire do so, the study's conclusions about "any activity" are "provocative." However, the findings need to be verified in studies that also include an intensity profile determined with recently developed accelerometer technologies, they concluded.