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

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.

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.

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/m². 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.

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.