Time for a change? Threshold for obesity in contemporary Japanese population

The obesity criteria for Japanese population are defined based on a cross-sectional study conducted 30 years ago. We aimed to examine the validity of a BMI of 25 kg/m² as a determinant of obesity in the Japanese population by assessing the association between BMI and the lifestyle-related diseases in a large and long-term cohort.

This cohort study included 162,136 individuals aged ≥40 years who participated in a medical health checkup program at Panasonic Corporation covering 166 operational sites from 2008 to 2023. The associations between BMI and the development of lifestyle-related diseases during the follow-up period were assessed using a multivariate Cox proportional hazards model. A restricted cubic spline function was applied to model the associations between BMI and disease risk. The BMI values associated with the doubling of HRs (compared with a reference BMI of 22 kg/m²) were examined.

The average follow-up duration ranged from 6 to 8 years depending on the outcome. Restricted cubic spline curves showed BMI values (kg/m²) associated with an HR of 2 (vs. 22 kg/m²): 24.6 for diabetes, 26.8 for hypertension, 32.3 for hypertriglyceridemia, 26.4 for low high-density lipoprotein cholesterol, 25 for high low-density lipoprotein cholesterol, 30.8 for coronary artery disease, 32.0 for stroke, and 25 for CKD after adjusting for covariates. Similar results were observed in subgroup analyses stratified by gender and age.

The appropriateness of the conventional BMI threshold of 25 kg/m² in Japan warrants reconsideration.