Non-linear relationship between body mass index and self-rated health in older Korean adults: body image and sex considerations.

Objectives: The purpose of this study was to investigate the association between body mass index (BMI) and self-rated health (SRH) in older adults aged over 65 years while examining the influence of self-perceived body image (SBI) and sex.
Methods: Raw data were obtained from the Korea Community Health Survey, which included BMI measurements of Koreans aged over 65 years (n=59,628). Non-linear relationships between BMI and SRH were analyzed separately for each sex using restricted cubic splines while controlling for SBI and other confounding variables.
Results: Men showed a reverse J-shaped association, while women showed a J-shaped association between BMI and poor SRH. However, including SBI in the model changed this association for men to an inverted U-shape showing a negative direction, with the highest risk of poor SRH observed in the underweight to overweight range. For women, a nearly linear positive relationship was observed. Regardless of BMI, those who perceived their weight as not "exactly the right weight" had a higher risk of poor SRH than those who perceived their weight as "exactly the right weight" in both men and women. Older men who thought they were much too fat or too thin had similar highest risks of poor SRH, whereas older women who thought they were too thin had the highest risk of poor SRH.
Conclusions: The findings of this study emphasize the importance of considering sex and body image perceptions when assessing the relationship between BMI and SRH in older adults, especially in men.