Cathelicidin (LL-37, hCAP18) concentrations are partially modulated in vivo by vitamin D. This potent antimicrobial peptide is involved in numerous antifungal, antiviral and antibacterial processes, which has led to its recognition as an important contributor to upper respiratory host defence. Upper respiratory tract infections are a problem widely reported in athletes and are associated with impaired training capacity( Reference He, Handzlik and Fraser 1 ). Recent research has implicated 1, 25-dihydroxyvitamin D3 (1, 25(OH)2D3) in cathelicidin biosynthesis, via vitamin D receptor complex-driven epigenetic modifications to the cathelicidin gene( Reference Vandamme, Landuyt and Luyten 2 , Reference Lowry, Guo and Borregaard 3 ). The aim of this pilot study was to identify if wintertime vitamin D3 supplementation of athletes (from November-March/April) influences plasma cathelicidin concentrations, compared to non-supplemented controls.
An enzyme-linked immunosorbant assay (ELISA) was used to quantify baseline and endpoint plasma cathelicidin concentrations in 44 stored samples obtained from 22 elite Irish athletes (18 male; 4 females)( Reference Magee, Pourshahidi and Wallace 4 ) (Hycult Biotech, Fronstraat, The Netherlands). Serum 25-hydroxyvitamin D (25(OH)D) concentration was measured in the previous study by ELISA (IDS Limited, Boldon, UK).
Mean (SD) age of athletes in the control and supplemented groups was 30(8) years and 23(7) years, respectively. Age was significantly different between treatment groups (P = 0·027).
* Difference between baseline and endpoint (significance P < 0·05, paired t-test).
Change in cathelicidin concentration from baseline was not significantly different between groups (median (IQR); control group −34·94(50·66) ng/ml vs. supplemented group −17·18 (51·80) ng/ml, P = 0·076). Wintertime vitamin D3 supplementation significantly increased 25(OH)D concentrations from baseline. There was no significant change in plasma cathelicidin concentration in the supplemented group. In the control group, 25(OH)D concentration did not significantly change from baseline however a significant decrease in plasma cathelicidin concentration was identified.
These findings may be owing to the small sample size and because both treatment groups were vitamin D sufficient (>50 nmol/L) at baseline( Reference Bhan, Camargo and Wenger 5 ). Nevertheless such results indicate that maintenance of vitamin D status over the winter months, with vitamin D3 supplementation, may attenuate the wintertime decrease in cathelicidin concentrations. Whether such maintenance of cathelicidin concentrations translates into a reduced incidence of upper respiratory tract infection and/or enhanced physical performance remains to be elucidated.
This study was funded by the Translational Research Group: Diabetes, Endocrinology & Nutrition, HSC Research & Development Division, Public Health Agency, Belfast and the Department for Employment and Learning, Northern Ireland. Ethical approval was obtained from the University of Ulster Research Ethics Committee (FCBMS-13–089) and the study was conducted according to the guidelines laid down in the Declaration of Helsinki.
