Vitamin D Deficiency and Depression in Thai Medical Students During COVID-19 Pandemic: a Cross-Sectional Study.

Introduction: Vitamin D deficiency is associated with osteoporosis, cancer, and autoimmune disease; evidence on its association with depression remains controversial. During the COVID-19 pandemic, preventive measures lead to reduced outdoor time and sunlight exposure, which is the major source of vitamin D. This study aims to assess the prevalence of vitamin D deficiency in Thai medical students during the pandemic and to determine its association with depression.

Methods: Medical students of year 4 and year 5 rotating in the Srinakharinwirot University Hospital who had no diseases associated with vitamin D deficiency and had not taken vitamin D supplement in the past year were invited to participate. Their total serum 25-hydroxyvitamin D levels were assessed with ELISA. Their demographic data were recorded, including age, sex, family income, class year, grade point average, current and history of psychiatrist-diagnosed psychiatric illnesses, other underlying diseases, and perceived difficulties in academic, relationship, substance use, and social supports. Students' depressive symptoms were assessed using the Thai version of Patient Health Questionnaire-adolescent (PHQ-A).

Results: A total of 63 female and 36 male medical students participated. 47.5% were year 4 and 52.5% were year 5. The mean vitamin D level was 21.7 ng/mL. The prevalence of vitamin D deficiency/insufficiency during the COVID-19 pandemic was 52.6% (using the cut-off of <20 ng/mL) or 69.5% (using the cut-off of <30 ng/mL). The mean vitamin D level in year 4 students was significantly lower than that in year 5 students (12.2 vs 30.2 ng/mL, t = -10.00, p < 0.01). Vitamin D level was associated with age (r = 0.38, p < 0.01) and sex (marginally) [t = -1.80, p = 0.07]. In linear regression analysis, vitamin D level remained associated with the year of class after adjusting for age and sex (B = 18.67, p < 0.01). The mean PHQ-A score was 5.8. 16 participants were identified to have depression. Vitamin D level was not correlated with PHQ-A score (r = 0.03, p = 0.80). In stepwise regression analysis, only total perceived difficulties score remained a predictor for PHQ-A score. In linear regression analysis, vitamin D level was not associated with PHQ-A score after adjusting for total perceived difficulties score (B = -0.02, p = 0.46).

Conclusion: The prevalence of vitamin D deficiency/insufficiency in Thai medical students during the COVID-19 pandemic was high (52.6% or 69.5%), probably owing to a lack of sunlight exposure. Nonetheless, vitamin D level was not associated with depressive symptoms, probably owing to the small sample size or delayed onset of depressive symptoms.