Sound mind in a sound body . . .

Dementia is such a tragedy, and causes such difficulty for spouses, children and others who are close to people with dementia, that we are likely to overestimate its prevalence. Only about 2% of people age 65 to 69 are diagnosed with dementia, and even at age 75 the prevalence is only 5%. However, about a third of people in their 90s have dementia. Let me disclose that this is personal, because my father has dementia. I prefer not to say much about it here, except that it makes me keenly aware of the personal and social costs of dementia, and of the kinds of resources and services that families coping with dementia need. I will write more about this subject in coming days.

We often assume that increasing prevalence of dementia is simply a price we pay for increasing longevity, but that is probably only partly true. Findings reported in the Annals of Internal Medicine, and described here, tell an astonishingly different story. This was what is called a prospective longitudinal cohort study, so it's a strong design. Of 1,740 people 65 and older, with normal cognitive function at the beginning of the study, after 6.2 years 158 of them had developed dementia. But for people who reported exercising for at least 15 minutes three times a week -- and that doesn't mean running wind sprints or playing tennis, it includes walking, swimming, and stretching, etc. -- the incidence was 13/1,000 person years, compared with 19.7/1,000 person years for people who exercised less -- that's about a 40% reduction in risk. And while there could be some doubt as to causation -- possibly people who are prone to dementia are also less likely to exercise for some reason -- it was the frailest people who benefited the most.

As we have discussed ad nauseum here, obesity, diabetes, and related cardiovascular complications are the biggest public health problems confronting the U.S. right now, and physical activity is even more important than diet in preventing them. People who get plenty of vigorous exercise generally don't even have to worry about their calorie intake, because their bodies will automatically regulate their appetites appropriately. Marketing of junk food certainly contributes to the problem, but we live in an environment with a new kind of toxicity -- an environment that poisons our behavior. Television makes us stupid, utterly corrupts our politics, and degrades our culture. It also makes us sick, kills us, and now it appears, may ultimately destroy our minds.

Turn it off and go for a walk.