Leading Edge / Spring 2011
Don’t Overdo It!

Women who exercise strenuously may be at greater risk of developing dementia later in life, study finds


Photo by Shanekato/istockphoto

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.

Read about the Rey Auditory Verbal Learning Test in Psychology & Neuroscience (PDF)

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.


Reader Comments

# 1
Posted by Rose on April 6th, 2011 @ 2:00 pm

They’ve been telling us women not to exert ourselves for hundreds of years, ostensibly “for our own good.” When are we going to stop listening?

# 2
Posted by Pharma Critic on April 12th, 2011 @ 8:57 pm

This article isn’t much different than an ad for an estrogen supplement. Studies like Tierney’s reinforce the age-old idea that women are inherently reproductively defective compared to men.

# 3
Posted by Scott Anderson on April 20th, 2011 @ 10:28 am

As a PhD Candidate in the Department of Exercise Sciences at the University of Toronto, specializing in research in the area of physical activity and chronic disease, I was concerned upon reading this story.

My initial shock was with the strong suggestion for women that “exercise, exercise, exercise… may be exactly the wrong advice.” My concern is with the underlying research from which this advice is based upon (J of Alzheimer’s Disease 22:1331-1338, 2010); a small cross-sectional study in 90 postmenopausal women that reports weak to moderate correlations between physical activity (measured by a recall questionnaire that is not validated) and neuropsychological tests.

There is in fact other data, in larger studies and prospective studies, that supports a reduced risk of cognitive dysfunction with increasing physical activity in both men and women (Jedrziewski et al., 2010; Middelton et al. J Am Geriatr Soc 58: 1322-1326, 2010; Scarmeas et al., JAMA, 2009). Indeed, the data from this study (J of Alzheimer’s Disease 22:1331-13138, 2010) seem too weak to support the bold statement that exercising vigorously is the wrong advice for women.

In addition, I was surprised with the discussion regarding the relationship between participating in strenuous exercise and neuropsychological test scores, pinning estrogen deficiency as the mechanism. After completing my MSc in the area of physical activity and estrogen deficiency, I find much error in the statement “Women who engaged in more exercise probably had lower estrogen over their life.” Data have clearly demonstrated that exercise itself is not the primary cause of menstrual cycle dysfunction, rather, it is exercise in the presence of an energy deficiency that can subsequently lead to menstrual cycle abnormalities and estrogen deficiency (Williams & De Souza, Hum Reprod Update. 2004 Sep-Oct;10(5):433-48, Williams et al. J Clin Endocrinol Metab. 2001 Nov;86(11):5184-93). Furthermore, disturbances are not confined to women who exercise vigorously. However, without supporting evidence that these women were indeed suffering from a subtle/severe menstrual cycle disturbance during their exercising years, and/or were not replacing the calories that they expended with exercise, it cannot be accurately concluded that these women probably had lower estrogen over their lifetime.

As a student in the Department of Exercise Sciences, we are taught to critically appraise the potential benefits and harms of exercise on all aspects of health. Indeed, evidence to date suggests that exercise is beneficial for cognitive health, not to mention important for modifying the risk for cardiovascular disease, diabetes and many other chronic diseases. In a time where we, as a society, face many issues with obesity and obesity related diseases, and as a senior student in a Faculty that promotes the importance of physical activity, I find it discouraging and worrisome that this article, based on relatively weak data, may “scare” women from participating in physical activity. Before recommendations as definite as avoiding vigorous activity are made, further, more substantive prospective studies are required.

Sarah L West
MSc 2007, PhD candidate
Department of Exercise Sciences
Faculty of Physical Education and Health

# 4
Posted by Scott Anderson on April 20th, 2011 @ 3:48 pm

We were dismayed to read this story suggesting that women who exercise strenuously may be at greater risk of developing dementia later in life. After reading the source research paper, we are shocked that the author would recommend reduced activity intensity on the basis of such uncertain results.

The study (J of Alzheimer’s Disease 22:1331-1338, 2010) found weak to moderate correlations between reported physical activity with neuropsychological test scores among 90 women. A physical activity questionnaire asked for recall of participation in strenuous activities (e.g., swimming laps, aerobics) and moderate activities (e.g., brisk walking, volleyball) from high school to menopause. The measure, however, has not been validated and reports an average of more than 5.5 hours of activity per week – an average well beyond the most recent Canadian accelerometer study, which puts vigorous activity at less than 0.5 hours per week for women ages 20 to 60 (Colley et al., Health Reports, 22, March 2011).

Moreover, other research on the topic rejects increased risk with more activity. Middleton and colleagues (J Am Geriatr Soc 58: 1322-1326, 2010) studied more than 9,000 women and found lifetime activity actually reduced the risk of cognitive impairment – and no effect of exercise dose. Another study of 1,880 people found risk of Alzheimer’s was decreased by 25% by some activity, but by 33% with much activity (Scarmeas et al., JAMA, 2009).

While U of T alumni appreciate lively stories of interesting research, they also appreciate nuanced discussions of careful, well-developed research – not to mention a balanced exploration of both sides of an issue. There is a huge body of evidence underpinning the simple statement, “Focus on moderate to vigorous aerobic activity throughout each week, broken into sessions of 10 minutes or more” (Public Health Agency of Canada website, 2011).

Responsible research demands that a much more substantive evidence base is required before we can possibly make a public recommendation that women should avoid vigorous activity.

Scott Thomas, PhD
Professor,
Faculty of Physical Education and Health
University of Toronto

Doug Richards, MD
Associate Professor,
Faculty of Physical Education and Health
University of Toronto

# 5
Posted by Scott Anderson on April 27th, 2011 @ 3:58 pm

Dr. Mary Tierney responds to the two comments above:

One concern was that our findings did not support the conclusion that more activity reduces the risk of cognitive impairment. Our findings, in fact, did show that greater amounts of moderate activity were significantly associated with better cognitive performance. There was also a concern that we found “weak to moderate correlations” between reported physical activity and cognition; however, we reported statistically significant parameter estimates based on multivariate regression analyses which are quite distinct from correlation coefficients. Greater amounts of strenuous activity were significantly associated with poorer performance on 5 of our 6 neuropsychological tests.

Comments specifically refer to two studies that supposedly refute our findings. However, Middleton et al. (2010) acknowledge that their cognitive measure was a very insensitive tool and unable to detect a dose response of exercise. We, on the other hand, used highly sensitive measures of cognitive function which allowed us to detect this relationship. Also Scarmeas’ et al. (2009) only studied older men and women and their likelihood of developing dementia whereas our study examined life-time exposure to physical activity in women before menopause. Therefore, the two studies are not comparable to ours.

While we recognize that our measure has not been validated and is a limitation, the measure we used was the same one used in a study of 110,599 California teachers (Dallal et al 2007). Consistent with this study, we reported 2.5 hours of strenuous activity per week. Although this is beyond the 0.5 hours per week reported in the Canadian accelerometer study, our sample included healthy well-educated women, who are known to engage in more physical activity (e.g., Lee et al 2007). The authors of the accelerometer study also caution this tool is likely to underestimate vigorous activity.

We agree that balanced reporting is important and that women should be informed of these findings. Exercise dose has been inadequately studied in humans to date and our findings provide support for the need for further work in the area before unfounded conclusions are brashly made.

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