Link Found Between Bone Loss and Mental Deterioration

By Michael Lewis

Mental deterioration that occurs with aging may put women at risk for increased bone loss, according to a report in the October issue of the Journal of the American Geriatrics Society. Compared with women whose bone mineral density (BMD), a measure of bone strength, was in the normal range, those with spine fractures had lower scores on standardized tests of mental abilities and greater overall deterioration in mental status.

The female hormone estrogen, which declines with age, may be a major factor in this equation. Estrogen replacement therapy (ERT) and blood levels of estrogens are associated with bone density and some recen studies have suggested that ERT may protect against mental decline and reduce the risk of dementia. The researchers say the findings add further support for the importance of maintaining adequate estrogen status and bone strength as women age.

"Could estrogen prevent both bone loss and cognitive function loss?"

"Certainly this makes one wonder about the role of estrogen," says lead researcher Kristine Yaffe, MD. Yaffe is an assistant clinical professor of psychiatry at the University of California in San Francisco. "Could estrogen prevent both bone loss and cognitive function loss?" Cognitive function refers to complex thought processes involved in learning and memory.

Approximately 10% of women over age 65 have cognitive function loss, or loss of some aspects of mental functioning, which puts them at risk for death and disability as well as greater likelihood of hospitalization and doctor visits. At least 30% of women in this age group have low bone density. Together, cognitive loss and low bone density are two of the most common conditions affecting older women.

The study population consisted of 8,333 women age 65 or older who were not taking estrogen replacement therapy and were not demented. Bone density was measured at the start of the study and again four to six years later. Mental abilities were measured by three standardized tests used to score various aspects of memory, orientation, and visual-spacial skills.

Women with decreased bone strength had poorer scores on the mental tests

Women with the lowest levels of bone density were found to be older and thinner and had more symptoms of depression. In addition, these women were older when they had their first menstrual cycle and younger when they went through menopause, compared to women with higher bone density. Also compared to women with higher levels of bone density, women with decreased bone strength had poorer scores on the mental tests. Women with spine fractures had the lowest mental test scores and greatest odds of mental deterioration.

Woman with the lowest bone density levels were more likely to have been diagnosed with dementia.

Performance on the mental tests worsened over time. At the four- to six-year follow-up, women with the greatest decreases in bone density had the greatest reduction in mental scores on all three tests. Compared with women with higher bone density, those with the lowest bone density levels were more likely to have been diagnosed with dementia.

According to Yaffe and colleagues, it is unlikely that bone density affects mental abilities directly, but poorer thinking may diminish physical activity and in turn lead to accelerated bone loss, or to weight loss that decreases bone strength and increases the risk of bone fractures.

Although estrogen deficiency is one probable link in the association between bone loss and loss of some mental abilities, other possibilities include depression and stroke, which have been shown to be associated with both low bone density and mental decline. Still another possibility, Yaffe says, is something called the "terminal drop" hypothesis, which states that as people age, multiple organ systems of the body fail simultaneously. While the study only included women, Yaffe says that the findings may be applicable to men as well.

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