Serum 25(OH)D Levels in Fragility-Fractured and Non-fractured Patients in a Low Latitude Region

Vitamin D is produced in nature in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). The measurement of serum 25(OH)D is the most accurate way to determine the amount of vitamin D in an individual. The association between 25(OH)D and fragility fractures (FxF) has been recognized for many years, but its direct role is unclear.

This study aimed to assess the association between serum 25(OH)D levels and FxF in a hospital-based population in the Colombian Caribbean (latitude ~10.3°), using a cross-sectional design with prospective data collection, while adjusting for confounders such as age, sex, skin phototype, BMI, grip strength, and comorbidities. Secondary objectives included exploring potential effect modification by skin phototype and describing the prevalence of vitamin D insufficiency in this low-latitude cohort.

A cross-sectional study with prospective data collection was performed comparing serum 25(OH)D levels between FxF and non-fractured (non-FxF) patients. Logistic regression, adjusted for age and sex, identified clinical characteristics associated with FxF.  Results: Forty patients with FxF were compared with 40 non-FxF participants. Women comprised 89% of the FxF group. The median age in FxF was 73 years (interquartile range (IQR) 62-80) and 75 years in non-FxF (IQR 62-80; p = 0.2037). Phototype III skin was most common and acted as a protective factor against FxF with a crude odds ratio (OR) of 0.29 (95% CI: 0.19-0.84; p = 0.011) and an adjusted OR of 0.27 (95% CI: 0.12-0.89; p = 0.015). No statistically significant differences in 25(OH)D levels were found between groups (FxF: 26.0 + 10.0 ng/mL; non-FxF: 26.9 + 10.3 ng/mL; p = 0.6991).

Both FxF and non-FxF patients showed insufficient 25(OH)D levels, echoing findings from Mendelian randomization studies suggesting no causal link between low vitamin D and FxF. Phototype III was the most common and was found to be protective. Phototypes V and VI were not observed in the study cohort. The inclusion of the hospital-based nature of the cohort may explain the overall vitamin D insufficiency and higher grip strength in the group with FxF. Further studies are required to assess the interaction of genetic and metabolic factors in this context.