Azara Blog: Exercise in midlife allegedly cuts risk of dementia

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Date published: 2005/10/04

The BBC says:

Exercising for half an hour at least twice a week during midlife can significantly cut a person's risk of dementia later, say researchers.

People in their late 40s and early 50s who do this could reduce their risk of dementia by about 50%, according to a study reported in Lancet Neurology.

Those who are genetically prone to Alzheimer's disease could see a reduction of about 60%, it adds.

The Swedish team said the findings had large disease prevention implications.

"If an individual adopts an active lifestyle in youth and at midlife, this may increase their probability of enjoying both physically and cognitively vital years in later life," they said.

Past studies have also suggested regular exercise might guard against dementia, however, this is one of the first to look at the effects over a long time scale - about two decades.

The authors say this is important because dementia takes many years to develop and is typically quite advanced when it is diagnosed.

The study involved nearly 1,500 men and women, of whom nearly 200 developed dementia or Alzheimer's disease between the ages of 65 and 79.

The researchers looked back at how physically active the study participants had been up to 21 years earlier, when they would have been in their late 40s and early 50s.

Those who developed Alzheimer's disease or another form of dementia were far less likely to have been active when they were middle-aged than those who remained free of dementia.
...
It might be that people who exercise tend to live healthier lifestyles in general, such as drinking less alcohol and refraining from smoking, they said. However, when they took into account such health risk factors, the findings remained the same, suggesting that exercise per se is beneficial for the brain.

A classic confusion of correlation and causation. As noted in the final paragraphs above, they tried to take other "risk factors" into account, but they certainly have not thought of everything. It's possible that your health outcome is already largely determined by the time you are (say) ten, and some people then are already predetermined to be both healthier in midlife (hence more likely to exercise) and healthier in late life (hence less likely to get dementia). The way to do this study properly is to take two randomly chosen groups, and force one group to do no exercise in midlife, and the other group to do lots of exercise, and then see what happens. Needless to say such a study would never be done. As such, the only conclusion one can make from the study that was done is that there is a correlation between exercise in midlife and not getting dementia. Of course there may be more than a correlation, only these researchers have not demonstrated it one way or the other.

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