Now we are all without excuse, at least when it comes to exercise. A new study on physical activity that involved more than half a million participants over age 40 found that modest exercise increases life expectancy regardless of weight.
That's right, it doesn't matter whether you are morbidly obese or have a normal body mass index (BMI), exercise helps you live longer regardless.
Counter to most of the attention given to obesity as the crucial risk factor for health, the study found that an active lifestyle increased life expectancy to a greater extent than a lower BMI, in general. In fact, participants who were active but class I obese lived an average of 3.1 years longer than those who were at a normal weight but didn't engage in physical activity. This is in-line with reports from earlier this year that excessive sitting is unhealthy and that reducing excessive sitting to less than 3 hours a day alone can improve longevity by 2.0 years.
The study, which was published in PLoS Medicine, involved pooled data from the six cohort studies carried out in the U.S. and Sweden involving over 650,000 individuals between ages 21-90, though the researchers focused on individuals that were over the age of 40 and excluded those who were underweight. Researchers from the National Cancer Institute, who authored the study, relied on self reported data that was part of others studies, including a diet and health study and a women's health study.
The physical activity of participants was gauged as metabolic equivalent hours per week (MET-hr/wk), in the following chart:
The article states that "participation in even a low level of leisure time physical activity of moderate to vigorous intensity...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." A low level of physical activity is defined as up to 75 minutes of brisk walking per week. They added, "a lack of activity and a high BMI (obese class II+) were associated with 7.2 y of life lost relative to meeting recommended activity levels and being normal weight. For comparison, long-term cigarette smoking reduces life expectancy by approximately 10 y."
The World Health Organization (WHO) recommends physical activity level of 150 minutes of moderate- to vigorous-intensity exercise per week (the 7.5 MET-hr/wk in the chart above). From this recommended amount up to twice this level (300 minutes per week), the benefit to life expectancy is 3.4 years. More than twice the WHO recommended level extended lifetimes by 4.2 years, on average.
The researchers concluded that for a given person, "adding even low amounts of leisure time physical activity to one's daily routine -- such as 75 min of walking per week -- may increase longevity" based on the findings.
Just looking at the chart, a couple of other interesting points can be made. First, even people who are morbidly obese and exercise are extending their lifetimes on average to the same extent as people of normal weight who are inactive. Also, whether people are of normal weight or severely obese, if they don't exercise they lose about the same number of years in life expectancy.
Finally, and this one is a bit rough, if someone has a healthy BMI and exercises a lot, but is about to fall off the wagon and repeat bad habits, it is much better to gain weight than to stop exercising rigorously. Gaining weight even to the point of being obese would reduce a person's life by 1.6 years, on average, but even if they stayed at a healthy BMI, but dropped to low activity levels, they'd lose 2.4 years, and if they stopped completely, 4.7 years.
Now these are statistical averages across gender and a spectrum of race and ages, but it's still worth considering to appreciate how the study indicates that exercise is a more important factor to longevity than weight, all other things being equal.
Personal longevity is a game of probability, so each factor that improves health shifts the distribution to longer lifespans. So while there are no guarantees for individuals, the results of this study strongly suggest that longevity does statistically improve for a population age 40 and over that exercises.
A consequence of this study is that it calls into question the reliance on BMI to assess fitness. Increasingly, what is needed is an exercise measure to more accurately gauge health, at least when it comes to longevity. That isn't to suggest that BMI isn't a factor, but that what we've heard for years in the media that being overweight is "bad" for you while exercise is "good" is a flawed message.
A better message would be: Regular exercise is essential to longevity and a lower BMI helps too -- do the first and the other will likely follow.