Association Between Body Mass Index and Fall Risk in Older Adults: A Cross-Sectional Study

Background Falls are a common health problem among older adults, with an incidence as high as 30%–50%. They can lead to physical injuries, functional decline, and even death, and have become a major public health concern. Body mass index (BMI) is a key indicator for assessing nutritional status. Previous studies have suggested that BMI is associated with the risk of falls; however, the dose–response relationship and potential nonlinear association between BMI and fall risk remain unclear. Therefore, this study aimed to examine the association between BMI and fall risk in older adults and to determine whether a U-shaped relationship exists. Methods This study employed a cross-sectional design and included 8,956 adults aged 60 years and older who were assessed using the Elderly Fall Risk Assessment System at a fall clinic of a tertiary hospital in Beijing between 2021 and 2024. Demographic characteristics, health status, and fall risk data were collected through structured questionnaires. Binary logistic regression models were used to examine the association between BMI and fall risk. Restricted cubic spline functions were applied to explore potential nonlinear relationships, and sex-stratified analyses were also conducted. Results BMI was positively associated with fall risk (OR = 1.02, 95% CI: 1.01–1.03). Restricted cubic spline analysis revealed a U-shaped relationship between BMI and fall risk: the lowest risk was observed at a BMI of 18.5–24 kg/m², while BMI values below or above this range were associated with increased risk. Subgroup analysis showed that high BMI (> 24 kg/m²) was significantly associated with an increased risk of falls (OR = 1.07, 95% CI: 1.03–1.11), whereas the association for low BMI (< 18.5 kg/m²) was not statistically significant. Sex-stratified analyses indicated that both high and low BMI were significantly associated with fall risk in women ( P  < 0.05), while no significant association was observed in men. Conclusions These findings suggest that weight management should be incorporated into fall-prevention strategies for older adults, and that individualized interventions should be developed for populations with different BMI levels and by sex. Trial registration No trial registration.(This study was a crosssectional study and did not involve any intervention.)