Determinants of vitamin D deficiency among undergraduate medical students in Saudi Arabia.

Background/objectives: The objectives of our study were to determine possible factors associated with low vitamin D levels in medical students.
Subjects/methods: A cross-sectional study was performed among 255 first- to fifth-year male undergraduate medical students of one of the major universities in Saudi Arabia. Serum 25-hydroxyvitamin D (25(OH)D) levels were measured using electrochemiluminiscence. Multiple logistic regression analysis was performed.
Results: Majority of Saudi medical students (75.2%) had 25(OH)D levels <30 nmol/l, defined as risk for deficiency by the Institute of Medicine. Multivariate analysis showed that the odds of having 25(OH)D serum levels of ⩾ 30 nmol/l were seven times higher both in students who took vitamin D (odds ratio (OR)=7.2, 95% confidence interval (CI)=1.8-29.9, P=0.006) or multivitamin supplements (OR=6.9, 95% CI=1.7-27.3, P=0.006) within 1 year. Students with a history of vitamin D testing >1 year before the study or moderate/vigorous physical activity (PA) had 4.4 (OR=4.4, 95% CI=1.7-11.4, P=0.003) and 2.7-fold (OR=2.7, 95% CI=1.3-5.3, P=0.006) higher odds of having 25(OH)D levels ⩾ 30 nmol/l, respectively. There was no significant association between 25(OH)D serum levels and average time spent outdoors per day (P=0.369) and type of clothing (long-sleeved vs short-sleeved; P=0.800).
Conclusions: Vitamin D deficiency was highly prevalent in Saudi medical students. Modifiable factors such as vitamin D intake and PA could be targeted for intervention. Further studies with standardized laboratory measurements of 25(OH)D are needed to explore the role of vitamin D testing in behavioral change, which may lead to increased serum 25(OH)D levels.