Body mass index in older persons is associated with Alzheimer disease pathology.

OBJECTIVE: We examined the extent to which body mass index (BMI) in older persons is associated with common age-related neuropathologies known to contribute to dementia including Alzheimer disease (AD) pathology, cerebral infarction, and Lewy body disease.
METHODS: We studied brain autopsies from 298 deceased Catholic clergy participating in the Religious Orders Study, a longitudinal clinical-pathologic investigation. BMI was assessed at annual clinical evaluations during an average follow-up of 4.9 years (SD = 2.7 years). Each person's average BMI, derived from all evaluations, was used in analyses. Multiple regression analyses were used to examine the relation of common postmortem neuropathologic findings to average BMI prior to death.
RESULTS: Mean age at death was 85.7 years (SD = 6.8 years), and average BMI during the course of the study was 26.0 (SD = 5.1). A series of linear regression models was performed with average BMI as the outcome and controlling for age, sex, and education. Level of AD pathology was associated with BMI proximate to death (estimate = -1.15; SE = 0.42; p = 0.007). However, Lewy body pathology (estimate = -0.45; SE = 0.73; p = 0.53) and cerebral infarctions (estimate = -0.10; SE = 0.61; p = 0.88) were not associated with average BMI. The association of AD pathology with BMI was unchanged after controlling for dementia, chronic diseases, and physical activity.
CONCLUSION: Body mass in old age is associated with Alzheimer disease pathology in persons with and without dementia.