Age-appropriate BMI cut-points for cardiometabolic health risk: a cross-sectional analysis of the Canadian Longitudinal Study on Aging.

Objectives: Body composition changes that occur with aging pose unique health risks to older adults. The current World Health Organization (WHO) body mass index (BMI) cut-points may not accurately reflect health risks in older adults (65+). Prior findings suggest those classified as overweight may be conferred survival advantages. This study aims to define age-specific BMI cut-points for adults (45-64, 65-74, and 75-85 years) associated with cardiometabolic outcomes, and compare the performance of these thresholds to the WHO BMI thresholds using cardiometabolic conditions and frailty as outcomes.

Methods: Using baseline data from the comprehensive cohort of the Canadian Longitudinal Study on Aging (N = 30,097), a classification and regression tree cross-sectional analysis was conducted to derive age-specific BMI cut-points based on cardiometabolic health risk. The area under the receiver operating curve (AUC), sensitivity, and specificity were estimated. Agreement with waist circumference was conducted.

Results: For older adults (65-74 and 75+ years old), the BMI threshold for identifying overweight increased to 26.9 and 26.6, respectively, from the WHO definition of 25.0 kg/m. For obesity, the thresholds were revised to 29.0 and 30.9, respectively, from 30.0. The largest improvements to AUC occurred in older adults (65+). Across all age-sex stratifications, the new overweight threshold demonstrated lower sensitivity and higher specificity compared to the traditional threshold. Age-specific BMI thresholds demonstrated higher agreement with waist circumference for some age-sex stratifications and poor performance with hearing.

Conclusions: Age-appropriate BMI thresholds for older adults may improve classification by health risk compared to standard WHO cut-points. A higher overweight threshold but lower obesity cut-points may be best suited to this demographic.