Dementia and osteoporosis are two of the most common health conditions affecting older women; interestingly, a new study finds a strong link between the two. Loss of bone density, which can be measured easily by X-ray, strongly correlates with cognitive decline in postmenopausal women. The findings also suggest that similar studies should be conducted in men.
Menopause is not normally associated with changes in memory or cognitive performance, but estrogen deficiency can cause cognitive impairment, and low estrogen level is also a risk factor for weak bones and osteoporosis. Women who have had both ovaries removed before the age of 45 are at significantly-increased risk of cognitive impairment and dementia. Studies suggest that women suffer Alzheimer's disease at up to three times the rate of men. Forgetfulness is the mildest form of cognitive decline in postmenopausal women, but 10-15 percent of women diagnosed with mild cognitive impairment will develop Alzheimer's disease.
The study, lead by professor Byung-Koo Yoon at the Department of Obstetrics and Gynecology at the Sungkyunkwan University of Medicine in Seoul, Korea involved 120 postmenopausal women who were experiencing various levels of cognitive decline, from mild forgetfulness to symptoms of early Alzheimer's disease. The researchers gave the women standardized neuropsychological tests and classified them into three groups based on the severity of their cognitive impairment. Their bone density was then measured by X-ray of their lower spine and hip.
The data, published in the current issue of the journal Menopause, shows a significant association between the amount of cognitive impairment and loss of bone density in both the lumbar spine and hip. Bone density was much lower in the group of women suffering early Alzhemier's disease than in the group of women with mild memory impairment, but there were no differences in smoking, nutrition, or exercise between groups. This is the first study to demonstrate that loss of bone density correlates directly with various stages during cognitive decline in aging.
Lower estrogen level is the likely explanation for the association between bone density and brain function. Estrogen therapy has been shown to prevent bone density loss and reduce fractures. Some studies suggest that estrogen therapy initiated early after menopause may reduce the risk of dementia, but the link between estrogen and cognitive impairment or dementia is less well understood than for estrogen deficiency and bone density. Estrogen may protect against the damaging effects of beta amyloid accumulation (the toxic brain plaques in early Alzheimer's disease), oxidative damage, and protect against stroke. Other studies, however, have associated hormone replacement therapy with increased cognitive decline. The Women's Health Initiative Memory Study demonstrated that oral hormone therapy of a certain combination of estrogen and progesterone increased the risk of developing dementia in women over 65 years of age.
"These results, however, should not be generalized to other regimes of hormone therapy or to younger women," Dr. Yoon says. Other forms of estrogen replacement therapy may provide greater benefits in improving cognitive function, according to some recent studies.
A similar relation between low bone density and cognitive decline might be expected in men, but this needs to be tested. "Bone loss in men is also related to estrogen deficiency," says Dr. Yoon.
Men are sensitive to the associated effects of a decline in testosterone level with age, but most men give low estrogen levels little thought. In a man's body, most of the estrogen comes from the conversion of testosterone, and testosterone and estrogen levels decline gradually in aging men. The consequences of low testosterone on decreased muscle mass, bone formation, immune function, libido, aggression, and age-related cognitive function are well appreciated. Several studies have found that testosterone treatment for older men with lower testosterone levels improved certain cognitive functions, but estrogen levels were not measured. The new results raise the question of whether declining estrogen levels might be a reason for the enhancement of cognitive performance in men just as in studies on women.
Dr. Yoon cited a 2011 study in the journal Neurobiology of Aging, conducted by researchers in Canada showing that estrogen treatment had a beneficial effect on tests of verbal memory and mild cognitive impairment in elderly men. In this study, half the men received estrogen and half received a placebo.
Now there is an additional reason to have a bone density screen in older age. Additional studies are needed, says Yoon, but "our results suggest an association between estrogen deficiency and cognitive aging. Estrogen would be good for osteoporosis, but it is not proven yet regarding cognitive decline." If a woman has low bone density the new results suggest that discussing estrogen treatment with their physician may be a useful option, especially if she is relatively early in the postmenopausal stage.
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