Yearlong fluctuations of vitamin D status, intake, and health outcomes in university students: A prospective longitudinal study

This longitudinal observational study examined changes in serum 25(OH)D concentration, C-reactive protein (CRP) concentration, vitamin D intake, cognitive function, depressive symptoms, and body composition in university students across an academic year. Methods: Participants (n = 49) completed four assessments (in October, January, March, and July) that included blood sampling for 25(OH)D, CRP, leptin and cortisol measurements, body composition via plethysmography, questionnaires, and cognitive testing. Results: Most students had insufficient 25(OH)D concentrations. Supplementation increased 25(OH)D only after three months, with levels declining when supplementation decreased. Vitamin D intake correlated with 25(OH)D concentration. CRP peaked in March despite the greatest frequency of infections occurring in January. Percent fat mass decreased from January to March, and fat-free mass (kg) was higher in March and July than in October and January. Cortisol concentration was the highest in October. Cognitive performance improved after October, while depressive symptoms were greatest in October. No significant associations were observed between 25(OH)D and CRP, body composition, cognition, and depression. Despite a significantly higher vitamin D intake in CYP2R1 rs10741657 GG homozygotes (58.0 ± 43.0 µg/day vs. 25.3 ± 34.6 µg/day, p = 0.0081) than in AG + AA genotypes, no significant differences in 25(OH)D concentrations were observed between these genotypes. Conclusions: University students were at risk of low vitamin D status throughout the year; only sustained supplementation led to an effective increase in 25(OH)D concentrations. CYP2R1 GG homozygotes may require higher intake levels of vitamin D in order to achieve comparable 25(OH)D concentrations to those with AG + AA genotypes.