Fit, Yet Fat? A Little Exercise May Add Years to Life

Diedtra Henderson

November 06, 2012

Middle-aged people who walk briskly for as little as 75 minutes per week may live 1.8 years longer, even if they are overweight. If they spend more time walking, running, swimming, cycling, or sweating in aerobics class, they may boost their life expectancy by 3.4 to 4.5 years.

Steven C. Moore, PhD, from the Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, and coauthors report the findings of their pooled analysis online November 6 in PLoS Medicine.

More than 100 epidemiological studies have sought to clarify the role that physical fitness plays in lowering mortality risk. Dr. Moore and colleagues went a step further by looking at gains in life expectancy associated with varying durations of physical activity during leisure hours and at varying body mass index (BMI) measurements. The analysis comes as US physical activity levels have plummeted and waistlines have bulged.

The researchers pooled 6 prospective cohort studies, including 654,827 participants aged 21 to 90 years. With such a large sample size, the researchers were able to examine years of life gained after age 40 years, according to varying activity levels and with such added granularity as mortality hazard ratios by smoking status and race. Slightly more than half (56%) of the participants in the pooled analysis were women, 96.4% were white, 2.4% were black, and the median age was 61 years. The researchers measured the energy cost of such leisure time activities as sports and exercise through their metabolic equivalent (MET). Moderate- or vigorous-intensity activities, for example, rank 3 METs, which is about the same intensity as walking briskly.

"[P]articipation in even a low level of leisure time physical activity of moderate to vigorous intensity — i.e., 0.1–3.74 MET-h/wk [hours per week], equivalent to less than half the [World Health Organization]-recommended activity level and comparable to up to 75 min of brisk walking per week — was associated with reduced risk of mortality during follow-up relative to no such activity. Assuming a causal relationship, this level of activity would confer a 1.8-y gain in life expectancy after age 40, compared with no activity," Dr. Moore and colleagues write. "At the minimum recommended physical activity level — 7.5–14.9 MET-h/wk, equivalent to 150–299 min of brisk walking per week — the gain in life expectancy was 3.4 y. At approximately two times the minimum recommended level — 15.0–22.4 MET-h/wk, which is equivalent to brisk walking for 300–449 min/wk — the gain in life expectancy was 4.2 y."

Remarkably, the association between physical activity and life expectancy held for every BMI.

In contrast, low physical activity was associated with a lower life expectancy and greater risk for death, which grew by BMI grouping. At the most extreme, a sedentary lifestyle and high BMI edged close to the mortality risk of smoking. Specifically, a normal-weight person who was inactive during leisure time lived an average of 4.7 fewer years compared with a normal-weight person who was active during leisure time. Meanwhile, inactivity was associated with a loss of 7.2 years from the lives of people with high BMI (35 kg/m2 or higher) compared with normal-weight people meeting recommended physical activity levels. In comparison, long-term cigarette smoking reduces life expectancy by 10 years.

"Mammoth" Study Praised

Geoffrey Godbey, PhD, professor emeritus of recreation, park, and tourism management at Penn State University, University Park, Pennsylvania, told Medscape Medical News the study is "worthwhile" and that its "mammoth" sample size is one of its strengths. He also noted that the study rightly focuses on leisure time, the arena during which people move their bodies the most (more than during paid work or housework).

"They're looking at the right part of life, in terms of physical activity," Dr. Godbey said.

"Physical activity above the minimal level — at recommended levels, or even higher — appears to increase longevity even further, with the increase in longevity starting to plateau at approximately 300 min of brisk walking per week," the authors conclude. "[A] lack of leisure time physical activity when combined with obesity is associated with markedly diminished life expectancy. Together, these findings reinforce prevailing public health messages and support them for a range of ages and backgrounds: both a physically active lifestyle and a normal body weight are important for increasing longevity."

Dr. Moore and colleagues are optimistic that their findings "may help convince currently inactive persons that a modest physical activity program is 'worth it' for health benefits, even if it may not result in weight control."

However, Dr. Godbey is not sure the findings will trickle down. People who are physically sedentary are "the most helped physiologically by 20 minutes per day of some kind of physical activity," he told Medscape Medical News. However, he added, this target population tends to be low-education, works in low-income jobs, shops in stores that lack fresh produce, lacks physicians or friends to coax them to exercise, and lives in neighborhoods that are too dangerous to go outside to exercise.

Study limitations include its reliance on self-reported leisure time physical activity, the tendency of overweight and obese participants to fudge by overreporting leisure time physical activity, and the study's focus on just the moderate- to vigorous-intensity leisure time physical activities. In addition, because it is an observational study, the researchers could not exclude the possibility of confounding by other ailments that afflicted the participants, their diets, and other factors.

The National Institutes of Health and the National Cancer Institute supported the study. One study author reported serving as a consultant to Virgin HealthMiles and serving on their Scientific Advisory Board. Among the studies included in the pooled analysis, the National Institutes of Health–AARP Diet and Health study and the US Radiologic Technologists study were supported by the National Cancer Institute; the Campaign Against Cancer and Stroke (CLUE) was supported by the National Institute of Aging and the National Cancer Institute; and the Swedish Women's Lifestyle and Health study is supported by the Swedish Research Council and Swedish Cancer Society.

PLOS Medicine. Published online November 6, 2012.