If you want to stay mentally alert well into old age, you should exercise, exercise, exercise. At least, that’s what the popular press would have us believe. For women, however, that may be exactly the wrong advice: new evidence suggests that, on the contrary, strenuous exercise hastens cognitive decline and increases risk of dementia.
Many studies have found that exercise protects the brain, but until now no study has compared different intensities of exercise. Mary Tierney, a professor of family and community medicine at U of T, became especially interested in that link after reading about a study where intense physical activity reduced women’s risk of breast cancer – by depleting their estrogen levels.
Estrogen, Tierney knew, protects the brain against cognitive decline. Could highly active women be depressing their estrogen levels enough to have a detectable impact on their cognitive well-being?
Tierney, who is also a senior scientist at Sunnybrook Research Institute, recruited 90 healthy post-menopausal women and asked about the amount and intensity of their physical activity throughout their adult life, in 10-year periods up to menopause. Strenuous activities included swimming laps, aerobic exercise, playing racquetball and running. Moderate activities included brisk walking, golfing, cycling on street level and playing softball. Tierney and her colleagues calculated the number of hours a week that each woman engaged in both strenuous and moderate activity, in exactly the way the breast cancer study had done.
Then the researchers tested the women on six neuropsychological tests. One, the Rey Auditory Verbal Learning Test, requires a subject to listen to a list of 15 simple words five times. Then, after reading a list of 15 other words just once, the subject is asked to recall the words from the first list. The test is highly predictive of Alzheimer’s disease up to 10 years in advance. “Women with the highest levels of strenuous exercise did the most poorly,” says Tierney.
Many active women refuse to believe the results. They feel at their peak when running marathons and tearing up the squash court. “But these results raise the concern that a lot of strenuous exercise may not be good for women,” says Tierney.
As in the breast cancer study, low estrogen is thought to be the cause. It takes a lot of energy to maintain the female reproductive system. Women exercising hard for many hours a week may not be ovulating normally – though they may not know it. This results in lower-than- optimal levels of estrogen being produced. “Women who engaged in more exercise probably had lower estrogen over their life,” says Tierney.
About a quarter of all people over the age of 65 have significant cognitive impairment, says Tierney, and eight per cent of those have full-out dementia. Women are at greater risk for Alzheimer’s disease than men. Part of the reason is that, after menopause, a woman’s estrogen levels plummet, and she relies on estrogen from other sources. (Older men, surprisingly, have more estrogen than older women.)
Her advice to women? “Engage in moderate activity as much as you can,” she says. But drop the iron-woman workout.