Red blood cell distribution width and risk of hip fracture in older adults: a UK Biobank prospective cohort study

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Red blood cell distribution width (RDW) is a routinely available hematologic marker that has been associated with aging-related adverse outcomes, but evidence regarding its association with hip fracture remains limited. This study aimed to examine the association between RDW and the risk of hip fracture in older adults. In this prospective cohort study, we included UK Biobank participants aged ≥ 65 years without a prior history of hip fracture. Baseline RDW values were obtained from complete blood counts at recruitment, and were analyzed as a continuous exposure. The primary outcome was incident hip fracture. Missing covariate data were addressed using multiple imputation. Associations between RDW and incident hip fracture were assessed using multivariable Cox proportional hazards models adjusted for relevant confounders. Restricted cubic splines were used to assess nonlinearity, and subgroup analyses by sex and anemia status were conducted to test effect modification. A total of 76,078 participants aged 65 to 73 years were included, with a median follow-up of 14.06 years (IQR 13.19 to 14.88 years). During the follow-up, 2,016 incident hip fractures occurred, with an incidence rate of 1.99 (95% CI 1.90 to 2.08) per 1,000 person-years. In multivariable Cox regression, each 1-percentage-point increase in RDW was associated with an 8% higher hazard of hip fracture (HR 1.08, 95% CI 1.03 to 1.13, P < 0.001). Restricted cubic spline analysis showed an overall association between RDW and hip fracture risk, with no evidence of nonlinearity ( P -overall = 0.001; P -nonlinearity = 0.448). In subgroup analyses, no evidence of effect modification by sex ( P for interaction = 0.795) or anemia status ( P for interaction = 0.532) was observed. Higher RDW was associated with an increased risk of hip fracture in older adults of both sexes after adjustment for measured covariates. As a routinely available hematologic index, RDW may warrant further evaluation as a potential component of fracture risk prediction models.