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This article originally posted 09 November, 2012 and appeared in  Physical ActivityIssue 651

Eleven, Yes Eleven Minutes a Day, Really

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.... 
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If you spend more time walking, running, swimming, cycling, or sweating in aerobics class, you can boost life expectancy by 3.4 to 4.5 years.

More than 100 epidemiological studies have sought to clarify the role that physical fitness plays in lowering mortality risk. Steven Moore of the U.S. National Cancer Institute 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.

"Participation 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.

The authors conclude that, "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." "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."

What do these findings really mean and will they ever trickle down? People who are physically sedentary are "the most helped physiologically by 20 minutes per day of some kind of physical activity. However, Dr. Moore 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.

PLOS Medicine. Published online November 6, 2012.  

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This article originally posted 09 November, 2012 and appeared in  Physical ActivityIssue 651

Past five issues: Diabetes Clinical Mastery Series Issue 198 | Issue 738 | Diabetes Clinical Mastery Series Issue 197 | Issue 737 | Diabetes Clinical Mastery Series Issue 196 |

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