Underweight as a Risk Factor for Vertebral Fractures in the South Korean Population.

BACKGROUND CONTEXT: Being underweight is a known risk factor for osteoporosis and sarcopenia that is strongly associated with vertebral fractures, particularly in the elderly. Being underweight can accelerate bone loss, contribute to impaired coordination, and increase fall risk in the elderly and the general population.

PURPOSE: This study aimed to identify the degree of underweight as a risk factor for vertebral fractures in the South Korean population.

STUDY DESIGN: Retrospective cohort study based on national health insurance database.

PATIENT SAMPLE: Participants were included from nationwide regular health check-ups conducted by the Korean National Health Insurance Service in 2009. Participants were followed up from 2010 to 2018 to identify the incidence of newly developed fractures.

OUTCOME MEASURES: The incidence rate (IR) was defined as the incident per 1,000 person-years (PY). Vertebral fracture development risk was analyzed using Cox proportional regression analysis. Subgroup analysis was performed based on several factors, including age, sex, smoking status, alcohol consumption, physical activity, and household income.

METHODS: Based on body mass index, the study population was categorized into normal weight (18.50-22.99 kg/m2 ), mild underweight (17.50-18.49 kg/m2 ), moderate underweight (16.50-17.49 kg/m2 ), and severe underweight (<16.50 kg/m2 ) groups. Cox proportional hazards analyses were performed to calculate the hazard ratios for vertebral fractures based on the degree of underweight with respect to normal weight to identify the associated risk.

RESULTS: This study evaluated 962,533 eligible participants, of whom 907,484 were classified as normal weight, 36,283 as mild underweight, 13,071 as moderate underweight, and 5,695 as severe underweight. The adjusted hazard ratio of vertebral fractures increased as the degree of underweight increased. Severe underweight was associated with a higher likelihood of vertebral fracture. The adjusted hazard ratio was 1.11 (95% confidence interval, 1.04-1.17) in the mild underweight group, 1.15 (1.06-1.25) in the moderate underweight group, and 1.26 (1.14-1.40) in the severe underweight group when compared with the normal weight group.

CONCLUSIONS: Underweight is a risk factor for vertebral fractures in the general population. Furthermore, severe underweight was associated with a higher risk of vertebral fractures, even after adjustment for other factors. Clinicians could provide real-world evidence that being underweight carries the risk of vertebral fractures.