Professor Mike Gleeson of Loughborough University in England is the senior author on a recent randomized controlled trial (RCT) of vitamin D supplementation for 14 weeks using blood and saliva antimicrobial functions as primary end points. First author Cheng-Shiun and colleagues randomized 49 university athletes to either 5,000 IU/day (20 subjects) or placebo (19 subjects), measuring serum cathelicidin and salivary antimicrobial functions (SIgA) before and after treatment.
Cathelicidin is a naturally occurring antibiotic that is directly upregulated by vitamin D. It is present in blood, respiratory and salivary secretions. SIgA is the most common type of salivary immunoglobulins. Salivary immunoglobulins are a group of complex proteins that protects humans from infection. The authors wanted to know what effect vitamin D supplementation would have on these antimicrobial functions.
Serum 25(OH)D increased from 22 ng/ml to 50 ng/ml at the end of 14 weeks in the treatment group. Serum 25(OH)D at 14 weeks ranged from 39 ng/ml to 60 ng/ml in the treatment group. As the study was done in winter, vitamin D levels in the placebo group fell from 22 ng/ml to 13 ng/ml, ranging from 10 to 20 ng/ml by the end of winter.
They found that serum cathelicidin increased by 15% in the treatment group and by 5% in the placebo group (P = 0.025). The resting SIgA and cathelicidin salivary secretion rates increased over time in the vitamin D3 group but not in the placebo group (P = 0.026 for SIgA and P=.030 for cathelicidin). They also found that resting salivary flow rates increased significantly in the treatment group (p<.05).
This RCT showed effects of vitamin D supplementation on important antimicrobial systems in the body, offering a possible mechanism that could explain why vitamin D reduces the risk of infection.
He CS, Fraser WD, Tang J, Brown K, Renwick S, Rudland-Thomas J, Teah J, Tanqueray E, Gleeson M. The effect of 14 weeks of vitamin D3 supplementation on antimicrobial peptides and proteins in athletes. J Sports Sci. 2015 Apr 10:1-8.