Body mass index, dementia, and mortality in the elderly

Objectives: To explore the association between body mass index and mortality in the elderly taking the diagnosis of dementia into account. Design: Cohort study. Setting: cohort study of aging in Medicare recipients in New York City. Participants: 1,452 elderly individuals 65 years and older of both genders. Measurements: We used proportional hazards regression for longitudinal multivariate analyses relating body mass index (BMI) and weight change to all-cause mortality. Results: There were 479 deaths during 9,974 person-years of follow-up. There were 210 cases of prevalent dementia at baseline, and 209 cases of incident dementia during follow-up. Among 1,372 persons with BMI information, the lowest quartile of BMI was associated with a higher mortality risk compared to the second quartile (HR = 1.5; 95% CI: 1.1,2.0) after adjustment for age, gender, education, ethnic group, smoking, cancer, and dementia. When persons with dementia were excluded, both the lowest (HR = 1.9; 95% CI =1.3,2.6) and highest (HR = 1.6; 95% CI: 1.1,23) quartiles of BMI were related to higher mortality. Weight loss was related to a higher mortality risk (HR = 1.5; 95% CI: 1.2,19) but this association was attenuated when persons with short follow-up or persons with dementia were excluded. Conclusion: The presence of dementia does not explain the association between low BMI and higher mortality in the elderly. However, dementia may explain the association between weight loss and higher mortality.