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The relationship of walking to dementia or mental function loss
(May 2005)

We all know that physical exercise has huge benefits (see Human Tune-Up). Several studies suggest that physical activity can also help prevent the mental decline (cognitive function decline) that often accompanies aging or can actually help in preventing dementia. Two articles in the Journal of the American Medical Association in September 2004 add significantly to the evidence, but still leave some important unanswered questions.

The first is from the Nurses' Health Study; 18,766 women over age 70 were tested for mental function using five test instruments; 16,466 of the women were re-tested one and one-half years later. The results were then related to physical activity, as determined on several questionnaires. The results were impressive. Those doing at least a modest amount of physical activity showed better cognitive functioning and there was a reasonable dose-response - the greater the total amount of leisure time physical activity, the better the mental function. The authors then looked specifically at walking and found "walking the equivalent of at least one and one-half hours a week at a 21 to 30 minute per mile pace was also associated with better cognitive performance". They then analyzed changes in mental function during the average one and one-half year followup as related to physical activity. Those doing a lot of leisure time exercise showed less mental function decline. They concluded that the benefits of greater physical activity were "similar in extent to being three years younger in age and were associated with a 20 percent lower risk of cognitive impairment" (mental function decline).

The other study, from the well-respected Honolulu Heart Program included 3,734 men ages 70 to 93 years. The risk of dementia was less in those who walked at least one mile a day and was particularly found in those who walked at least two miles a day compared to men who walked less than one-quarter mile a day. There was also some evidence that risk of dementia was greater among men who were slower walkers.

The authors concluded "our findings suggest that physically capable elderly men who walk more regularly are less likely to develop dementia".

Commentary: These are interesting studies, but there are some substantial unresolved issues.

- In the women's study, there were pretty big differences in baseline characteristics among those doing more exercise and those doing less. Those doing more exercise took more vitamin E, had less high blood pressure and coronary heart disease, smoked less, used anti-depressants less, and had more energy. Some of these differences were adjusted for; some were not. And, vitamin supplement use (aside from vitamin E) was not analyzed; that is a mistake because vitamins other than vitamin E may relate to mental function, and greater vitamin use among those doing more exercise could explain, at least in part, the results

- In the men's study, many of the differences in dementia risk were not statistically significant; the results were most impressive for an increased Alzheimer's risk among sedentary men (walking less than one-quarter mile a day).

- Other studies on dementia have generally found no, or only a weak, association with walking.

- Most important, it is not clear how vigorous the walking needs to be to effect a benefit in maintaining mental function or preventing Alzheimer's. The men who had reduced Alzheimer risk did a lot of walking, 7 to 14 or more miles a week and there was a suggestion that the faster walkers (how fast is not clear) were those who benefitted most.

In the women's study, the authors give conflicting statements about how vigorous the walking needs to be. They say walking at an easy pace for one and one-half hours a week is clearly beneficial, but the only table relating to that statement does not support that conclusion. It is hard to tell whether walking at the easy pace (one mile every thirty minutes) for longer periods (at least two hours a week) was beneficial or whether a faster pace was required.

- It also seems possible that those with incipient mental function decline or incipient dementia might walk less because of a variety of fears and anxieties.

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Walking probably is good for the mind. It may well help protect against loss of mental functioning with aging and may even protect against dementia, but we need more studies and we must know how vigorous the exercise needs to be to provide the protection. Perhaps the most important message from these and many other studies is: try not to be sedentary.

Weuve, J., et al. Physical activity, including walking, and cognitive function in older women.

Abbott, R.D., et al. Walking and dementia in physically capable elderly men.

Journal of the American Medical Association. Vol 292 (September 22) Pgs 1447-1458, 1454-1461. 2004.

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