An association between head circumference and Alzheimer's disease in a population-based study of aging and dementia.

We investigated the association between head circumference (HC) and Alzheimer's disease (AD) in a cross-sectional population-based study of aging in North Manhattan. Six hundred forty-nine subjects underwent neurologic, neuropsychological, and anthropometric evaluations; apolipoprotein E (apoE) genotype was available for a subsample of 300 individuals. Logistic regression analyses were performed with AD the outcome of interest to evaluate any association between HC and AD. In these analyses, HC evaluated as a continuous variable was associated with AD (OR 0.8, 95% CI 0.7-0.9) after adjusting for age, education, and ethnicity, gender, and height. Analyses suggested that increased risk resided mainly in those with smallest HC. Thus, women whose HC was within the lowest quintile of HC for women were 2.9 (95% CI 1.4-6.1) times more likely to have AD, after adjusting for age, education, and ethnicity; and men in the lowest quintile of HC (for men) were 2.3 times more likely to have AD (95% CI 0.6-9.8). There was no confounding by height, weight, or apoE genotype. The results are consistent with previous studies that suggest that premorbid brain size may influence the age-specific risk for AD. Future epidemiologic studies seeking environmental risk factors for AD may benefit by making HC measurements on all subjects to decrease the variance associated with other potential risk factors.