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

Abstract

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.