In an article published recently in JAMA’s Archives of Neurology, researchers from the Research and Training Institute of Hebrew SeniorLife reported the results of a study that indicated a significant association between low bone mineral density (BMD), particularly in the lower femoral neck portion of the skeleton, and an increased incidence of Alzheimer’s disease in women.
Spurred by results of earlier studies that suggested that estrogen levels may be associated with dementia in postmenopausal women, Institute researchers wanted to find out whether there is a relationship between BMD in older adults and development of dementias such as Alzheimer’s disease. According to the paper, BMD may be a surrogate marker for cumulative estrogen exposure. The production of estrogen among individual women varies due to factors such as pregnancy history and age at menopause, as well as exposure from external sources like diet or medications. Higher BMD may reflect a higher exposure to estrogen in the body.
Led by Zaldy Sy Tan, M.D., M.P.H., the researchers conducted a prospective study that examined data on 987 subjects (610 women and 377 men) from the original Framingham Heart study. The subjects all lived in the community, were cognitively intact, and had baseline BMD measured at three skeletal sites between 1988 and 1989. When the investigators looked at data indicating which subjects developed dementia, the results were significant. Women in the lowest quartile for femoral neck BMD had more than twice the risk of developing Alzheimer’s disease than did those in the other three quartiles. The femur is the long bone that extends from the hip to the knee. The femoral neck is that part of the femur that connects the ball joint, referred to as the femur head, to the shaft of the bone.
According to lead author Dr. Tan, “The strong association between BMD and the risk of dementia found in this study suggests an important link in the pathogenesis of two of the most common age-related conditions, namely osteoporosis and memory disorders. However, he cautions, “Since this is the first study to report this potential relationship, the results must first be confirmed by other studies before the current standards of care for these conditions are modified.”
Previous studies, like the one conducted by the Women’s Health Initiative, have elicited concern regarding the safety of taking long-term post-menopausal estrogen replacement, which has been shown to increase the risk of dementia. However, lifelong estrogen exposure was not considered in the design of previous studies.
In their paper, Institute researchers suggest that controlled trials of prophylactic ERT may be justified in women with low BMD if further studies confirm the strong association between low BMD and dementia in women.