Vitamin D supplementation augments SIgA secretion rates in Marine Corps basic trainees

BACKGROUND: Vitamin D has been implicated in modulating innate immunity and may confer protection against upper respiratory tract infections (URTIs) during periods of arduous training. PURPOSE: Determine whether vitamin D status in Marine Corps basic training recruits is associated with URTIs, and whether daily vitamin D supplementation decreases the incidence of URTIs as a result of augmented innate immunity. METHODS: A double-blind RCT was conducted with male and female recruits entering Marine Corps basic training. Subjects were randomized to either 1000 IU vitamin D3·d-1 (n=73) or placebo (n=76) for 12-weeks. At baseline, weeks 4, 8 and 12 (post-training) subjects provided saliva samples (passive drool) to determine secretory immunoglobulin A secretion rates (SIgA-SR) by indirect ELISA. The incidence of URTIs was assessed by administering a survey at weeks 4, 8 and 12. Serum vitamin D status (25(OH)D) was measured by radioimmunoassay. Longitudinal linear models were created using a simple-effects model to estimate symptoms. To determine whether supplementation altered SIgA-SR during training, a two-way repeated measures ANOVA was used. RESULTS: The proportion of recruits reporting URTI symptoms at any time during training was 72%. Baseline SIgA-SR were similar between placebo (65.4 ± 52.0 μg·min-1) and vitamin D groups (51.9 ± 41.9 μg·min-1). The relative changes in SIgA-SR were significantly greater with vitamin D supplementation at weeks 4 (5.1 ± 29.8%) and 8 (12.3 ± 31.0%) compared to placebo at the same time points (week 4; -6.5 ± 22.9% and week 8; 1.3 ± 22.9%), p = 0.001. Baseline 25(OH)D was significantly lower during winter (59.2 ± 22.5 nmol·L-1) compared to summer (80.4 ± 21.0 nmol·L-1), p < 0.001. When accounting for treatment, season and sex, there was no association between 25(OH)D and reported URTIs. CONCLUSION: We report that a high proportion of Marine Corps recruits experience URTIs during 12-weeks of basic military training, and although daily vitamin D supplementation led to a modest increase in SIgA-SR, this did not result in a reduction in the incidence of reported URTIs.

Duke Scholars

Author Heath Gasier Anesthesiology