BMI and all-cause mortality among middle-aged and older adults in Taiwan: a population-based cohort study.

OBJECTIVE The present study investigates the relationship between BMI and all-cause mortality among middle-aged and older adults with or without pre-existing diseases. DESIGN A population-based cohort study. SETTING The Taiwan Longitudinal Study on Aging is a nationwide prospective cohort study comprising a representative random sample of middle-aged and older adults. The study period was 1996-2007. SUBJECTS We followed 4145 middle-aged and older adults, totalling 42,353 person-years. RESULTS Overweight and mildly obese participants showed a 16% and 30% decrease in the risk of death, respectively, compared with those of normal weight after adjusting for potential covariates (e.g. demographic characteristics, health behaviour, co-morbidities and physical function). Underweight adults showed a 1.36-fold increased adjusted hazard ratio of death compared with normal-weight adults. Adults with a BMI of 27.0-28.0 kg/m(2) showed a significantly lower adjusted hazard ratio of all-cause mortality rate compared with adults who had normal BMI values when they had coexisting hypertension or diabetes (adjusted hazard ratio = 0.50; 95% CI 0.30, 0.81 for hypertension and adjusted hazard ratio=0.41; 95% CI 0.18, 0.89 for diabetes). CONCLUSIONS The study demonstrates that underweight people have a higher risk of death, and overweight and mildly obese people have a lower risk of death, compared with people of normal weight among middle-aged and older adults. An optimal BMI may be based on the individual, who exhibits pre-existing diseases or not.