What’s the best ‘dose’ of exercise?

Exercise is a great medicine. Study after study has found that it can help reduce the risk of heart disease, diabetes, cancer, dementia and many other chronic illnesses. 

Recently, though, some research has suggested that exercise in high doses can be harmful, particularly to the heart. For example, a Danish study published earlier this year found that high-intensity, high-mileage runners die at a similar rate as people who don’t engage in any kind of regular physical activity.

These “too much exercise may be bad for you” findings have led to some confusion. Just how much should we be exercising, and at what intensity? In other words, what dose of exercise is optimum for our health?

In an article published earlier this month in the Journal of the American Medical Association (JAMA), two experts on the topic of exercise and health, Thijs Eijsvogels, of Radboud University in the Netherlands, and Dr. Paul Thompson, a cardiologist now at Hartford Hospital in Connecticut, attempt to answer that question. They reviewed all the best research on this topic, and came up with the following conclusions:

• First of all, doing something is better than nothing. As Eijsvogels and Thompson point out, research has demonstrated that people who daily engage in 15 minutes of moderate-intensity activity (brisk walking, dancing or gardening) or just eight minutes of vigorous activity (running, fast cycling or competitive sports) tend to live longer than their inactive peers — an average of three years longer in one study.

• Moderate levels of exercise — a minimum of 30 minutes daily of moderate-intensity activity or 75 minutes weekly of vigorous activity — is associated with significant health benefits. Furthermore, when it comes to brisk walking and other moderate-intensity activity, more is better — to a point. One study found that people who exercised at a moderate pace for 38 to 96 minutes a day had the lowest risk of dying from heart disease. Once people exceeded 100 minutes a day, however, they were unlikely to reap an additional health benefits. Yet — and this is an important point — that extra exercise didn’t appear to be harmful, either.

• The more-is-better mantra may not be true, however, for vigorous exercise, such as running. For example, in the Danish study published earlier this year, runners who exercised more than three times a week for more than four hours at a fast pace had the same mortality rate as non-runners. People who followed a less intense running schedule, on the other hand, had a much lower mortality rate than their non-running peers.

As Eijsvogels and Thompson note, the studies that have raised warnings about too much vigorous exercise have certain methodological flaws that may limit the validity of the findings. (Indeed, most studies examining the relationship between exercise and various health risks are flawed in the sense that they tend to be observational. That means they can show only a correlation between exercise and mortality rates, not a direct connection.)

The two researchers also stress that “no dose of vigorous physical activity is associated with higher mortality rates than physical inactivity.”

“Physical activity,” they conclude, “is one of the best modifiable factors for the prevention of noncommunicable diseases and mortality.”

And that makes it one of the best medicines we can take — at any dose.

You’ll find an abstract of Eijsvogels and Thompson’s article at the JAMA website, but, unfortunately, the full article is behind a paywall.