The authors wrote, “Vitamin D supplementation may lower the risk of acute respiratory infection (ARI), and the effects may be mediated through the induction of cathelicidin production.”
The objective of the double-blinded, randomized, controlled trial (RCT) was to examine the effect of vitamin D supplementation on ARI and cathelicidin concentration and to study the associations between baseline serum 25 hydroxyvitamin D (25[OH]D) and ARIs and cathelicidin concentrations in a 14-week follow-up study.
Data for the analysis were gathered and reviewed from military conscripts at two locations from January through May and conducted during 2018 and 2019. All patients were men aged between 18 and 29 years. The primary outcomes were the number of ARIs diagnosed and the number of days off because of ARI.
For this study, the participants were randomized into two groups to receive either 20 mcg of vitamin D3 or an identical placebo daily. Blood samples were obtained three times: at the beginning (Study Week 0), mid-term (Study Week 6), and at the end of the study period (Study Week 14). The follow-up study had 412 voluntary young men from two different locations and seasons (January and July).
A total of 184 patients (mean [standard deviation (SD)] age, 19 [1] years) were included in the RCT, of whom 76 received vitamin D supplementation and 88 received a placebo. No significant variances were observed between the supplementation and the placebo groups regarding baseline characteristics, the number of ARI diagnoses, days off duty due to ARI, or cathelicidin concentrations. However, patients with insufficient vitamin D levels experienced more ARIs than the total study population. During the 14-week follow-up period, 123 patients withdrew from the study.
At baseline, the average serum 25(OH)D levels in the placebo group at the beginning of the study were 57.0 ± 15.6 nmol/L and 55.5 ± 13.2 nmol/L in the supplementation group, respectively. In Study Week 6, the mean vitamin D level was 48.1 ± 11.2 nmol/L in the placebo group and 54.8 ± 13.0 nmol/L in the supplement group. In Study Week 14, the mean vitamin D level was 51.7 ± 12.1 in the placebo group and 59.7 ± 13.6 in the supplement group.
A total of 412 patients (average [SD] age, 19 [1] years) were included in the follow-up study, of whom 184 were enrolled in January and 228 were enrolled in July. The average baseline vitamin D level across both groups was 68.5 ± 20.0 nmol/L. Stratified by the time of enrollment, patients who began the trial in January exhibited significantly lower average vitamin D levels compared with participants who began in July (56.3 ± 14.5 vs. 78.3 ± 18.5 nmol/L; P <.001). Approximately one-third (33.7%) of patients enrolled in January had insufficient vitamin D levels compared with 5.3% of those enrolled in July.
In a multivariable-adjusted logistic regression analysis, insufficient vitamin D levels at baseline were associated with augmented risk for ARI (odds ratio [OR], 2.11; 95% CI, 1.19-3.74) and days off duty due to ARI (OR, 2.26; 95% CI, 1.27-4.03). However, vitamin D insufficiency was inversely related with cathelicidin concentration (OR, 0.49; 95% CI, 0.24-0.99).
Based on their findings, the authors concluded, “The present study shows that there is a possible preventive association between sufficient serum 25(OH)D and ARIs, and the association could be through the induction of cathelicidin production.” The researchers also noted, “Further RCT research is needed to determine the optimal amount of vitamin D supplement for the possible preventative effect.”
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