Abstract

Vitamin D (VD) is essential for bone and metabolic health, and its deficiency represents a public health issue in Chile, particularly among older adults and women of reproductive age. However, no longitudinal studies have analyzed its evolution in patients receiving care at healthcare facilities. This study evaluated the temporal trend of plasma VD levels in a hospitalized population treated at the Regional Hospital of Talca (HRT) between 2019 and 2023, considering differences by sex, age, and seasonality. An observational, longitudinal, and retrospective study was conducted based on 29,260 VD measurements. Levels were classified according to the Institute of Medicine (IOM) criteria. Prais-Winsten regression was used to analyze temporal trends, and spectral analysis was applied to assess seasonality. A statistically significant decreasing trend in VD levels was observed men (beta =-0.110; p = 0.034). Children under 14 years showed the highest VD levels (27.4 +/- 13.1 ng/mL), while older adults (>= 65 years) had the lowest (22.1 +/- 12.1 ng/mL). From age 45 onward, women showed significantly higher values than men (p < 0.010). A seasonal pattern was identified, with reduced VD levels during winter (f = 0.084; p < 0.050). Since the data come from a hospitalized population, the results are not necessarily generalizable to the general Chilean population. Still, they provide valuable information for the implementation of Chile's Food Fortification Law with VD (2026) and highlight the need for supplementation strategies in high-risk groups.