Serum vitamin A concentration and the risk of hip fracture among women 50 to 74 years old in the United States: A prospective analysis of the NHANES I follow-up study

Background Recent studies on the association between vitamin A and fracture risk have focused on samples with high vitamin A intake. We analyzed a cohort that was more representative of the overall U.S. population to test the hypothesis that both high and low serum vitamin A concentrations increase the risk of hip fracture. Methods We utilized data on 2799 women who were 50 to 74 years of age from the first National Health and Nutrition Examination Survey Epidemiologic Follow-up Study. There were 172 incident hip fractures during the 22-year follow-up period. Using Cox regression analysis, we analyzed the relation between baseline serum vitamin A (retinol and retinyl esters) concentration, as a continuous variable and by quintiles, and hip fracture risk. Results While there was no linear relation between serum vitamin A concentration and the risk of hip fracture in the multivariate analysis (hazard ratio [HR] per SD INCREASE = 1.0; 95% confidence interval [CI]: 0.9 to 1.2), analysis by quintiles revealed a U-shaped relation between serum vitamin A concentration and hip fracture. Fracture risk was significantly higher among subjects in the lowest (HR = 1.9; 95% CI: 1.1 to 3.3) and highest (HR = 2.1; 95% CI: 1.2 to 3.6) quintiles compared with those in the middle quintiles. Conclusion Both low and high serum vitamin A concentrations may be associated with an increased risk of hip fracture.