The relationship between body mass index and disability-free survival in elderly Japanese: the Ohsaki Cohort 2006 Study.

BACKGROUND: The relationship between body mass index (BMI) and disability-free survival (DFS) remains unclear.

METHODS: We conducted a 10-year prospective cohort study of 12,666 Japanese individuals aged ≥ 65 y. Information on BMI and lifestyle factors was collected via a questionnaire in 2006. Functional disability data were retrieved from the public Long-term Care Insurance database. Subjects were divided into seven groups according to BMI (<19, 19-21, 21-23, 23-25, 25-27, 27-29 and ≥29). Fiftieth percentile differences (PDs) and 95% confidence intervals (CIs) in the DFS period (differences of period until the first 50% of the composite outcome (disability or death) occurred in each of the BMI groups) were calculated using the Laplace regression model.

RESULTS: There was a U-shaped relationship between BMI and the risk of incident composite outcome, with a BMI nadir of 25-27. Based on BMI 25-27 as a reference, the 50th PDs (95% CIs) (in months) in age at disability or death (median DFS) were -20.8 (-26.4, -15.2) (P < 0.001) months for BMI <19, -13.5 (-18.2, -8.7) (P < 0.001) months for BMI 19-21, -9.8 (-14.2, -5.4) (P < 0.001) months for BMI 21-23, -2.9 (-7.5, 1.7) (P = 0.21) months for BMI 23-25, -2.7 (-8.4, 2.9) (P = 0.34) months for BMI 27-29, and -11.5 (-19.6, -3.5) (P = 0.005) months for BMI ≥ 29. These relationships did not differ by sex.

CONCLUSION: Older individuals with a BMI of <23 or ≥29 have a significantly shorter DFS period than those with a BMI of 25-27. It is suggested that the optimal BMI range for maximization of disability-free life expectancy in the elderly population is 23-29.