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At a recent dinner party, a geeky friend of mine was cheerily justifying the piles of money he spends on a personal trainer. He's feeling so great that it's worth every cent, he exulted, "And the best part is the return on the time! Every minute you spend working out comes back to you, because you'll live that much longer!"
"Really?" I wondered. I knew vaguely that being active lengthens life expectancy, but was the return on time spent really 1 to 1?
Certainly, I hoped it was. It's a daily struggle to make the time to exercise, and the current federal health guidelines call for at least 150 minutes a week of moderate exercise — a lot of time that somehow manages to seem like even more, magnified by the "should" it adds to so many days. There are hundreds of other reasons to exercise, and the one that works best for me is wanting to feel at my best on that very day. But it would be very comforting, I thought, if I knew that all of that time would come back to me.
Not only do you get the time back, it comes back to you multiplied — possibly by as much as seven or eight or nine.
Let me cut to the happy conclusion: It seems that it does. And then some. If you play with the data of a recent major paper on exercise and longevity, you can calculate that not only do you get the time back; it comes back to you multiplied — possibly by as much as seven or eight or nine.
To quote Tom Anthony, a regular CommonHealth reader with a Harvard physics degree who kindly helped me with the math, "I wish I could get these paybacks in the stock market."
This is all a bit of a public health parlor game, of course, resting on averages and approximations. You, personally, could work out ten hours a week and still die flukishly young. But the math looked so striking that I asked for a reality check from Dr. I-Min Lee of Brigham and Women's Hospital, a Harvard professor and senior author of that recent paper, "Leisure Time Physical Activity of Moderate to Vigorous Intensity And Mortality: A Large Pooled Cohort Analysis."
Yes, she confirmed, she had not calculated out the question before, but according to her data, a middle-aged person who gets the recommended 150 minutes per week of moderate exercise — defined as the level of brisk walking — can expect a 1-to-7 return: seven extra minutes of life gained for each minute spent exercising.
The paper on exercise and longevity broke ground by calculating for the first time the gains in life expectancy from various levels of activity. In the past, researchers had found that in general, being active gains people from two to four years of life, though some calculations concluded that it was a wash, that active people gained only as much time as they spent exercising.
(Of course, Dr. Lee noted, it's not just how long you live, it's how well, and exercise is key to quality of life, particularly in older age: "My mentor said it best: It's not the years you add to your life, it's the life you add to your years.")
Dr. Lee's paper drew on pooled data from six large studies that included more than 650,000 people followed over ten years, and showed that people who exercised at the recommended level gained 3.4 years of life after age 40. According to its numbers, she said:
Say you start with someone 45 years old who begins to follow the 150-minute-a-week recommendation. Average American life expectancy is 78. So: "If you start exercising at 45 and you die at 78, that means that you exercise for 33 years, at 150 minutes a week. I calculated that over 33 years you would need to spend basically 4,290 hours in exercise, which is 179 days of exercise, which is less than half a year. So that's half a year, and you gain almost three and a half years, so it is worth exercising. That's an approximate scenario using reasonable assumptions, and you're getting a 1-to-7 return."
And, I asked, what if you exercise more vigorously than the brisk-walking level?
In general, she said, more strenuous exercise has approximately double the effect. So, for example, 75 minutes of jogging has roughly the effect of 150 minutes of brisk walking. "So instead of gaining seven times the time spent, you'd be gaining 14 times."
The curve of gain tapers off at some point.
Back-of-the-envelope math aside, many caveats are in order, including Dr. Lee's warning that the gains do not extend infinitely. (If they did, wouldn't we be able to live forever so long as we spent every minute exercising? Feels like a science fiction story waiting to be written.)
“Yes — if you do a little, you gain a little; if you do more, you gain more,” she said. “But the curve of gain tapers off at some point. We aren't sure exactly at what point the risks outweigh the benefits. But this point is clearly higher than most people would do. The most common risks are musculo-skeletal injuries; we know these occur more frequently with longer duration and/or more intense physical activity." Also, people who have long been sedentary and suddenly start exercising — like the classic snow-shovelers who keel over — run heart risks.
The message, she says, is: "If you do nothing now, just start with a little bit of exercise. If you already do a little bit, try to get the 150 minutes that are recommended. And our current recommendations say that if you're willing to go up to 300 minutes, you do get additional benefits."
Tom Anthony's math came out very similar:
Computing years of life gained after age 40, running for two hours a week should gain you about four years of life. "So that is roughly 100 hours per year for your remaining 40 years or 4,000 hours in total for all 40 years. In one year, there are 24 hr/day X 365 days = 8,760 hours. So four additional years is 8,760 hr/yr X 4 yr = 35,040 hours of life gained. To gain these extra hours, you expended 4,000 hour of running. So the payback ratio is 35,040 hours gain/ 4,000 hours expended = 8.8.
Running for an hour gives you 9 hours of extra life.
Brisk walking for an hour gives you 2.9/8 X 9 = 3.2 hours of extra life.
Biking for an hour at less than 10 mph gives you 4/8 X 9 = 4.5 hours of extra life
Rope jumping for an hour gives you 10/8 X 9= 11 hours of extra life
Calisthenics for an hour gives you 8/8 X 9 = 9 extra hours of life
Here's a bit more from the press release on Dr. Lee's study, adding some interesting data about obesity and exercise that I'd sum up as "Better to be a bit fat and fit than normal weight but inactive":
“We found that adding low amounts of physical activity to one’s daily routine, such as 75 minutes of brisk walking per week, was associated with increased longevity: a gain of 1.8 years of life expectancy after age 40, compared with doing no such activity,” explained I-Min Lee, MD, associate epidemiologist in the Department of Preventive Medicine at BWH and senior author on this study. “Physical activity above this minimal level was associated with additional gains in longevity. For example, walking briskly for at least 450 minutes a week was associated with a gain of 4.5 years. Further, physical activity was associated with greater longevity among persons in all BMI groups: those normal weight, overweight, and obese.”
The findings show that physical activity was associated with longer life expectancies across a range of activity levels and BMI groups. Participation in a low level of leisure time physical activity of moderate to vigorous intensity, comparable to up to 75 min of brisk walking per week, was associated with a 19 percent reduced risk of mortality compared to no such activity.
Assuming a causal relationship, which is not specifically demonstrated in this research, this level of activity would confer a 1.8 year gain in life expectancy after age 40, compared with no activity. For those who did the equivalent to 150–299 min of brisk walking per week--the basic amount of physical activity currently recommended by the federal government--the gain in life expectancy was 3.4 years. These benefits were seen in both men and women, and among white and black participants. Importantly, they were also observed among persons who were normal weight, overweight, and obese. Participants faring best were those who were both normal weight and active: among normal weight persons who were active at the level recommended by the federal government, researchers observed a gain in life expectancy of 7.2 years, compared to those with a BMI of 35 or more who did no leisure time physical activity (a 5 ft 5 in tall person with BMI of 35 weighs 210 lb).
Readers, will this help motivate you? Defensive couch potatoes who are also quantitative thinkers, do you care to challenge this math somehow? Dr. Lee's paper is here for the full data.
This program aired on March 15, 2013. The audio for this program is not available.
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