Friday, September 23, 2011

Exercising will delay cognitive decline, or maybe not

We're seeing this sort of statement all around. Consumer Reports has said it. When I just updated my Epocrates, there was a little news item about this.

Here's the problem. This is not accurate. It's not necessarily wrong, but has yet to be proven, and this is a kind of research that many people don't understand, at least in terms of how to understand it.

What we actually have are a number of population studies, in which someone looks at a variably large number of people, and then analyses them by collecting data. One kind of data will be who has cognitive impairment and who doesn't. But also various lifestyle things might be looked at, like amount of exercise, how regular it is, etc.

So it has become clear that there is something of a match up between those who exercise and those who retain cognitive function better than their peers. So obviously, exercise causes a retention of cognitive abilities, right? Not necessarily.

All this really says is that there is some commonality, and it might work in the other direction, in other words, maybe people who exercise do so because they are more cognitively with it. How can that be? Well, why do people exercise? Have they been exercising because they knew it would keep them more cognitively fit too? Seems unlikely.

We actually already know that an early sign or marker of dementia can be social withdrawal.While I suppose that there are those who exercise in social isolation, exercising is very much a social sort of thing for the most part. At any rate the reasons why people exercise are not simple, and while there may be many who would like to exercise, there is something different about those who actually end up doing it.

The real answer to this question of the cognitive benefit of exercise would have to come from some controlled experiment, where you take one random group and force them to exercise, and another group where you prevent them from exercising. And I might as well add that we're not likely to see that happen, since you also have to do this for a number of years, since this isn't something that happens in 6 months.

So I'm not making an argument against exercise, I'm just trying to clarify some misimpressions that are floating around about it.

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