Job demands, job resources, and burnout among metro site management personnel in China: a cross-sectional study based on the JD-R model.

Depression is among the most prevalent global mental health disorders, affecting more than 300 million individuals worldwide, with adult women experiencing nearly twice the prevalence observed in men []. It is a leading cause of disability and is associated with reduced quality of life, increased suicide risk, and substantial socioeconomic burden. Women remain at higher lifetime risk because of interacting biological, psychological, and social factors. Although antidepressant pharmacotherapy and psychotherapy serve as first-line treatment modalities, their efficacy is limited, with response rates of approximately 50.0%~60.0%. Adverse effects and relapse further underscore the need for complementary therapeutic strategies. Growing interest has focused on nutritional influences on mental health, particularly vitamin D. Traditionally recognized for its role in calcium homeostasis and bone metabolism, vitamin D also exerts broader neurobiological effects []. Vitamin D receptors (VDRs) are expressed in several brain regions involved in mood regulation and neuroplasticity, including the hippocampus, prefrontal cortex, and hypothalamus. Additionally, vitamin D modulates serotonin synthesis through regulation of tryptophan hydroxylase expression, and has been associated with increased brain-derived neurotrophic factor (BDNF), which supports neuronal survival and function [,]. Epidemiological evidence consistently associates low vitamin D levels with depression. Meta-analyses have reported significant associations between vitamin D deficiency and increased risk of depressive symptoms [], and prospective cohort studies have indicated that insufficient vitamin D levels predict subsequent depressive symptoms []. Adult women are particularly vulnerable to vitamin D deficiency because of hormonal changes associated with pregnancy, childbirth, and menopause, making them a priority population for supplementation research. Studies have reported high prevalence of vitamin D deficiency in women with metabolic conditions such as prediabetes and type 2 diabetes [,].