Effects of vitamin D supplementation on salivary immune responses during Marine Corps basic training.

Vitamin D's role in regulating immune responses may increase during periods of elevated psychological and physiological stress. Due to the high demands placed on US Marine Corps recruits undergoing 12 weeks of basic military training, we hypothesized that vitamin status would be related to markers of innate mucosal immunity, and daily vitamin D supplementation would augment immune responses during training. Males (n = 75) and females (n = 74) entering recruit basic training during the summer and winter volunteered to participate in a randomized, double-blind, placebo-controlled study. Subjects received either 1000 IU vitamin D3 + 2000 mg calcium·d-1 (n = 73) or placebo (n = 76) for 12-weeks. Saliva samples were collected pre-, during (weeks 4 and 8), and post-training (week 12) for measurement of salivary SIgA and cathelicidin (indices of mucosal immunity) and stress (α-amylase). Initial (baseline) and post-training serum 25(OH)D levels were assessed. Results were as follows: Serum 25(OH)D levels were 37% higher in recruits entering training in summer compared to winter. A positive relationship was observed between baseline 25(OH)D levels and SIgA-secretion rates (-SR). When stress levels were high during summer training, baseline 25(OH)D levels contributed to an increase in SIgA-SR and cathelicidin-SR, the latter only in males. Vitamin D supplementation contributed to the changes in SIgA-SR and cathelicidin-SR, specifically SIgA-SR was higher in the treatment group. These data highlight the importance of vitamin D and mucosal immune responses during arduous basic military training when stress levels are increased. This article is protected by copyright. All rights reserved.