Association Between Waist-to-Height Ratio Estimated Fat Mass Categories and Incident Fractures

Although obesity is a well-known risk factor for various metabolic disorders, its impact on fracture risk remains uncertain. The inconsistency in findings may be due to the fact that most studies have relied solely on body mass index (BMI) as the measure of obesity. Other indices, such as waist circumference (WC) and the waist-to-height ratio (WHtR), have been suggested as better indicators of obesity. This study aimed to evaluate the association between obesity and fracture risk by using multiple obesity measures, including WHtR, WC and BMI, in a longitudinal cohort.

In this prospective cohort study, we analysed data from 5905 participants in the Korean Genome and Epidemiology Study (KoGES), with a median follow-up of 16 years. Participants were categorized into tertiles based on WHtR, WC and BMI, and the incidence of overall fractures and site-specific fractures (vertebral, hip and wrist/humerus) was assessed. Multivariate Cox proportional hazards models were used to examine the association between WHtR, WC, BMI and fracture risk, adjusting for potential confounders.

Among 5905 participants (54% women; age range, 40-69; median age, 50 years; interquartile range, 44-59), 816 fractures were reported over a median follow-up period of 16 years. A one-standard deviation increase in WHtR was associated with a 55% higher risk of overall fractures (adjusted hazard ratio [aHR] 1.55, 95% confidence interval [CI] 1.37-1.75), with similar trends observed for vertebral (aHR 1.60, 95% CI 1.13-2.26), hip (aHR 1.85, 95% CI 1.40-2.43) and wrist/humerus fractures (aHR 1.42, 95% CI 1.16-1.74). A one-unit increase in WC was linked to a 16% higher risk of overall fractures (aHR 1.16, 95% CI 1.08-1.24). BMI was not significantly associated with the fracture risk. Within the same obesity group defined by BMI, participants in the higher WHtR tertiles had a greater incidence of overall fractures. Specifically, individuals in the third tertile of WHtR with a BMI of ≥ 23 to < 25 kg/m² or ≥ 25 kg/m² had a higher risk of overall fractures compared to those in the first tertile of WHtR with a BMI < 23 kg/m² (aHR 1.88, 95% CI 1.34-2.62, and aHR 1.93, 95% CI 1.30-2.87, respectively).

Although a high BMI has often been considered a protective factor against fractures, this study found that obesity, as measured by WHtR, is a risk factor. Even among individuals with a high BMI, those with elevated WHtR should receive additional medical attention to help prevent fractures.