Last week I wrote twice about exercise. Strictly speaking, both stories were complete lies.
The first story was about a study published in the Lancet which analyzed data from more than 10,000 patients at 2 VA Medical Centers and found that patients with high fitness levels were less likely to die than patients with low fitness levels. The pattern held true whether patients were taking statins or not taking statins. The researchers concluded:
“Statin treatment and increased fitness are independently associated with low mortality among dyslipidaemic individuals. The combination of statin treatment and increased fitness resulted in substantially lower mortality risk than either alone, reinforcing the importance of physical activity for individuals with dyslipidaemia.”
Look carefully at that. The association of fitness and low mortality leads to the recommendation about “the importance of physical activity.” An accompanying editorial went further, recommending that “prescription of physical activity should be placed on a par with drug prescription.” Widespread media coverage of the study followed suit, with nearly all reports emphasizing the positive effects of exercise.
So what’s wrong here? It almost seems churlish to insist on the point, but of course the study (like all other observational studies) didn’t– couldn’t– actually say anything about the real effect of exercise on health. It seems reasonable to assume that more exercise leads to increased fitness leads to improved health. That’s what we all probably think and believe. It’s common wisdom. But it’s not entirely unreasonable to suppose that healthy people are much more likely to exercise, in effect reversing the cause and effect. And of course there may be other confounding factors that cloud the simple equation of exercise and health.
There’s more: even if you could prove that more exercise leads to better health that wouldn’t lead to an automatic conclusion that doctors should recommend exercise as much as drugs. First you would need to prove that an exercise prescription is just as effective as a drug prescription. It’s hard enough to get people to take inexpensive, life-saving drugs once a day. Is there any reason to think we can get any kind of effective level of compliance with an exercise prescription?
The other exercise story from last week had a much different conclusion. Editorialists in Heart concluded that although most exercise is good for you, too much exercise can actually be harmful. They may well be right, but there’s never been– and there almost certainly never will be– a good, properly designed randomized trial that could prove this theory. It’s entirely possible (in fact, almost certain) that people attracted to extreme endurance sports are different in many ways from the rest of us, and it’s quite plausible that some of those differences may have significant effects on health. Confounded again.
The last thing I want to do is trash exercise. I’m a big supporter of it. But these standards shouldn’t be compromised. So what is the proper way to report this kind of study? Here’s a brief, completely responsible version of the story (written by Kelly Young for Physician’s First Watch):
Click to continue reading…