Here's a new study that, a few years ago, I would have completely ignored. After all, its findings – greater aerobic fitness predicts longer life – are right up there with "water is wet" as a surprising discovery. However, in light of all the recent debate about the dangers of too much exercise, I think it's worth starting to pay more attention to these studies. They may be common, but that's part of the reason they get ignored by the media in favor of "surprising" findings.

The study, by researchers at Johns Hopkins, was just published as a letter in the Journal of the American College of Cardiology. Researchers followed 37,855 patients from the Henry Ford Exercise Testing Project, all of whom had performed a progressive treadmill test to determine their aerobic (a.k.a. cardiorespiratory) fitness. The patients were followed for an average of 11.5 years to see who died; aerobic fitness was expressed as "metabolic equivalents" (METs), which are basically multiples of your basal metabolic rate. If your peak treadmill load is 10 METs, it means you're burning 10 times as much energy as you do when lying on the couch at the point you have to step off the treadmill.

So here's the key data from the paper, showing how peak fitness affects all-cause mortality in different age groups:

You'll notice that the results are divided into the three fitness groups: 10-11 METs, 12-13 METs, and greater than 14 METs. In every case, the highest-fitness group fares best.

This is particularly interesting because back in 2012, in one of their many editorials and reviews warning about the dangers of too much exercise, James O'Keefe and Carl Lavie make the following claim: "[F]itness levels above 12 metabolic equivalents do not seem to translate into additional gains in CV health and longevity."

They base that claim on data from a 2005 study of patients at the Cooper Clinic, and include a graph showing that death from cardiovascular disease is slightly higher for subjects with fitness of 13 METs or greater compared to those with fitness of 12 METs. If you look up the original paper, you find that there were 242 patients in the 12 MET group, of whom 5 died, and 250 patients in the >13 MET group, of whom 6 died. Needless to say, there's no way to extract any conclusion from that (and the original authors of the study didn't try).

The new study fills that gap with a much bigger dataset, and makes it quite clear that there are still health benefits to be gained from fitness above 12 METs. In fact, they include a graph that plots their results out to 16 METs. They also note that "exploratory analysis suggested a continued mortality decrease" beyond 16 METs, but they didn't have enough patients to have sufficient statistical power to include that data in the results. If only all researchers displayed such caution!

Anyway, here's the graph of higher fitness levels:

I don't have a good sense of what, say, 14 METs corresponds to as a measure of fitness. (This link suggests that 8-10 METs is typical for a healthy middle-aged man or woman, while marathon runners can get up to 18 to 24.) As I mentioned above, the new JACC paper is just published as a very short letter; presumably more detailed results will eventually be presented elsewhere, which will provide more context. But if I had to pick a place on that graph above, I'd rather be at 18 than 8!

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