Vitamin D Deficiency in Preclinical Medical Students: Neuroendocrine, Cognitive, and Immune Effects

Vitamin D is increasingly recognized as a multifunctional hormone that extends beyond its traditional role in skeletal health to influence neuroendocrine regulation, cognitive performance, and immune function.Preclinical medical students represent a population at particularly high risk for vitamin D deficiency because of prolonged indoor study, limited sunlight exposure, sedentary lifestyles, and demanding academic schedules.This narrative review examines current evidence regarding vitamin D metabolism and its effects on the hypothalamic-pituitary-adrenal axis, stress resilience, cognition, neuroprotection, and immune homeostasis, with specific relevance to preclinical medical education.Available studies consistently demonstrate a high prevalence of vitamin D deficiency among medical students worldwide, with rates frequently exceeding 70%.Emerging evidence suggests that inadequate vitamin D status may contribute to impaired stress adaptation, mood disturbances, neuroinflammation, reduced cognitive performance, and immune dysregulation.However, the evidence is limited by the predominance of observational and crosssectional studies, variability in definitions of vitamin D sufficiency, heterogeneous study populations, and a lack of prospective investigations evaluating causality.Furthermore, data from U.S. medical student populations are limited.Despite these limitations, optimization of vitamin D status through lifestyle modification, dietary measures, and appropriate supplementation may support student well-being and academic success.Further research is needed to clarify prevalence, determine optimal vitamin D targets for neurocognitive health, and evaluate the effectiveness of preventive and therapeutic interventions in medical trainees.