Older women who are physically fit show less decline in their brain structure and their ability to perform mentally challenging tasks.
That's true even when the women use hormone replacement therapy to offset side effects of menopause, treatment that normally leads to a decline in brain mass and cognitive ability over time.
The positive effects of exercise appear to help offset the negative effects of hormone replacement therapy on the brain, especially in women using the treatment longer than 16 years, but also in intermediate users at 11 to 15 years.
Meanwhile, short-term hormone replacement therapy, a decade or less, actually appears to benefit the brain. The effects of exercise combine with the hormone therapy benefit to provide something of a double whammy, according to a new study by University of Illinois researchers.
The brains of older women who aren't on hormone replacement therapy benefit from exercise as well.
"Fitness benefited everyone," UI psychology Professor Art Kramer said recently.
Postdoctoral researcher Kirk Erickson and Kramer, for whom the effects of exercise on the brain are a research focus, examined 54 post-menopausal women for the study.
The participants, 58 to 80, were surveyed about their hormone use – estrogen and estrogen and progesterone in combination for those who used hormone therapy – and examined for aerobic fitness using a treadmill test.
The UI researchers then scanned the women's brains using magnetic resonance imaging and determined the volume of their gray and white brain matter with voxel-based morphometry, a computerized method of turning the MRI scans into brain volume data.
The women also went through cognitive tests designed to show propensity for dementia and to test their memories and their command of so-called "executive functions," such as task switching, which can be important in driving, among other things.
Declines in gray and white brain matter volumes have been associated with declines in cognitive function. The women in the UI study who were fit, besides having greater brain matter volume, also scored better on the cognitive tests, Erickson and Kramer said.
People in general tend to lose gray matter as they age. Kramer and colleagues had found previously that exercise appears to help stem the loss.
Other studies have noted a decline in gray matter with long-term hormone replacement therapy, but only in some cases. The UI study may help explain the disparity by showing that fitness, something the earlier studies didn't cover, can be an intervening factor.
Hormone replacement therapy didn't affect brain white matter volume in the UI study, but exercise improved it, something Kramer also had found in a previous study.
Researchers using animal studies have found that both estrogen and fitness stimulate brain-derived neurotrophic factor, a molecule that aids in recovery from brain trauma and promotes neuron and capillary growth, improving the brain's wiring and the vital blood flow it receives.
Kramer said hormone replacement therapy may have diminishing returns because it also promotes brain-degrading inflammation after a point. That doesn't appear to be the case with exercise.
"Exercise seems to exert its (positive) effects throughout the life span," said Kramer, who's also a professor at the UI's Beckman Institute.
The UI researchers outline the study of the older women in the journal Neurobiology of Aging. Stanley Colcombe, a research scientist at Beckman, postdoctoral researcher Paige Scalf, graduate student Steriani Elavsky and UI professors Edward McAuley in kinesiology and Donna Korol in psychology also worked on the study. The research was funded by the National Institute on Aging and the Institute for the Study of Aging.