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 cross-sectional 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.