[Associations of serum micronutrients with osteoporotic fracture]

Objective: To evaluate the relationship between serum micronutrient levels, including calcium, phosphorus, iron, and 25-hydroxyvitamin D, and the incidence of osteoporotic fracture. Methods: A retrospective analysis was performed in 5 984 patients hospitalized in the Department of Osteoporosis, West China Fourth Hospital, Sichuan University, from December 2017 to October 2024. The patients with osteoporotic fracture were divided into case group and those without osteoporotic fracture were divided into control group. Missing data were addressed using multiple imputation. Logistic regression model was used to analyze the association between different micronutrient levels and fracture risk, and mediating effect of bone mineral density was further evaluated. Model discrimination was evaluated using receiver operating characteristic curve and area under the curve (AUC), and differences in AUC were compared by DeLong test. Results: The calcium, phosphorus, and iron levels were significantly lower in patients with osteoporotic fracture than in controls, the difference was significant (all P<0.05). After adjustment for age, sex, BMI, and comorbidity, including diabetes, coronary heart disease, and hypertension, the logistic regression analysis showed that calcium level was significantly inversely associated with osteoporotic fractures, and phosphorus, iron, and 25-hydroxyvitamin D were not significantly associated with osteoporotic fractures. After additional mutual adjustment for phosphorus, iron and 25-hydroxyvitamin D, the association between calcium and fracture remained stable (OR=0.88, 95%CI: 0.82-0.94, P<0.001). This relationship was consistent in different subgroups, with no significant interactions. Bone mineral density had no effect to mediate the association between micronutrients and fracture. Using calcium level in the baseline model significantly increased the AUC, enhancing its discriminative ability (P=0.002). Conclusions: In patients with osteoporosis, the serum calcium levels showed an inverse association with fracture risk, and maintaining adequate calcium may help reduce this risk. The etiological roles of other serum micronutrients, including phosphorus, iron, and 25-hydroxyvitamin D, remain to be further analyzed.