Women who are heavy in their middle years are at greater risk of Alzheimer's disease, especially if they have large waists. However, for men, being underweight during that period of life actually increases the likelihood of developing the degenerative brain disease, researchers report in the American Journal of Epidemiology.
In addition, changes in weight had different effects on the risk of developing Alzheimer's disease for men and women.
"In future studies, investigators should address optimal age- and gender-specific health weight and weight loss strategies for prevention of AD," Dr. May A. Beydoun of the National Institutes of Health in Baltimore and her colleagues conclude.
Previous research has identified gender differences in the relationship between body mass index (BMI) and Alzheimer's disease risk, Beydoun and her team note, but scientists do not understand why, or agree on how changes in BMI might be related to Alzheimer's. To investigate, the researchers looked at 2,322 men and women participating in the Baltimore Longitudinal Study of Aging.
During the study's 23-year follow-up period, 187 participants were diagnosed with Alzheimer's disease.
Men who were underweight -- meaning they had a BMI of 18.5 or below -- at age 30, 40 or 45 were at more than five-fold greater risk of Alzheimer's than men who were normal weight at those ages. For women, being obese -- that is, having a BMI of 30 or greater -- and having excess belly fat at 30, 40 or 45 boosted risk more than six-fold.
Furthermore, while men who gained a significant amount of weight between 30 and 50 were 3.7 times more likely to develop Alzheimer's than those whose weight held steady, weight loss between age 30 and 45 actually doubled the risk for the disease for women.
Weight loss could signal underlying disease processes related to the development of Alzheimer's disease, Beydoun and her team suggest, noting that other researchers have found that people with mild cognitive impairment who lose weight or are underweight are more likely to develop Alzheimer's.
There also appear to be close relationships between fat- and appetite-regulating hormones and brain function, the researchers add, while both excess fat and decline in mental function have been linked to inflammation.
SOURCE: American Journal of Epidemiology, November 15, 2008.