Influence of Vitamin D Supplementation by Simulated Sunlight or Oral D3 on Respiratory Infection during Military Training

Abstract

To determine the relationship between vitamin D status and upper respiratory tract infection (URTI) of physically active men and women across seasons (study 1). Then, to investigate the effects on URTI and mucosal immunity of achieving vitamin D sufficiency (25(OH)D ≥50 nmol•L-1) by a unique comparison of safe, simulated-sunlight or oral D3 supplementation in winter (study 2). Methods: In study 1, 1,644 military recruits were observed across basic military training. In study 2, a randomized controlled trial, 250 men undertaking military training received either placebo, simulated-sunlight (1.3x standard erythemal dose, three-times-per-week for 4-weeks and then once-per-week for 8-weeks) or oral vitamin D3 (1,000 IU•day-1 for 4-weeks and then 400 IU•day-1 for 8-weeks). URTI was diagnosed by physician (study 1) and Jackson common cold questionnaire (study 2). Serum 25(OH)D, salivary secretory immunoglobulin A (SIgA) and cathelicidin were assessed by LC-MS/MS and ELISA. Results: In study 1, only 21% of recruits were vitamin D sufficient during winter. Vitamin D sufficient recruits were 40% less likely to suffer URTI than recruits with 25(OH)D <50 nmol•L-1 (OR (95% CI) = 0.6 (0.4-0.9)); an association that remained after accounting for sex and smoking. Each URTI caused on average 3 missed training days. In study 2, vitamin D supplementation strategies were similarly effective to achieve vitamin D sufficiency in almost all (≥95%). Compared to placebo, vitamin D supplementation reduced the severity of peak URTI symptoms by 15% and days with URTI by 36% (P < 0.05). These reductions were similar with both vitamin D strategies (P > 0.05). Supplementation did not affect salivary SIgA or cathelicidin. Conclusion: Vitamin D sufficiency reduced the URTI burden during military training.

25-Hydroxyvitamin D potentializes extracellular cathelicidin release from human PBMC stimulated ex vivo with either bacterial (LPS) or viral (P: IC) mimetics

“…The meta-analysis performed by Acen et al (2021) does not have sufficient eligible studies to perform a correlation meta-analysis of vitamin D and LL-37 levels [ 12 ]. Recent studies in vitamin D–supplemented volunteers failed to enhance cathelicidin plasmatic level [ 13 , 14 ]; our team observed the same absence of effect in a placebo-controlled clinical trial with vitamin D supplementation in elderly volunteers [ 15 ]. Despite a strong improvement in serum 25(OH)D concentrations, we found no variation in LL-37 serum concentrations.…”

Select Dietary Supplement Ingredients for Preserving and Protecting the Immune System in Healthy Individuals: A Systematic Review

“…The search strategy yielded 3928 unique publications once duplicates were removed across databases ( Supplementary File S2 ). Thirty-nine RCT studies (across 43 publications) met eligibility criteria including eight dietary supplement ingredients: echinacea (N = 6; n = 1708 subjects) [ 14 , 15 , 16 , 17 , 18 , 19 ], elderberry (N = 1; n = 312) [ 20 ], garlic (N = 2; n = 266) [ 21 , 22 , 23 ], vitamin A (N = 2; n = 1719) [ 24 , 25 ], vitamin C (N = 3; n = 237) [ 26 , 27 , 28 ], vitamin D (N = 18; n = 19,309) [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ], vitamin E (N = 1; n = 652) [ 49 , 50 ] and zinc (N = 6; n = 1445) [ 51 , 52 , 53 , 54 , 55 , 56 ], involving populations including children, adults and seniors, exposed to stressors described as stressful air travel, intense exercise, academic stress, exposure to winter months, environmental stressors such as poor living environments or where deficiency in certain nutrients is prevalent, and subjects inoculated with a virus. After title and abstract screening, the authors decided to exclude prebiotic and probiotic studies ...…”

“…One study involved older adults where approximately 25% had baseline levels <50 nmol/L [ 29 ]; seven studies involved adults with mean baseline levels ranging from 58 to 75 nmol/L [ 30 , 36 , 39 , 42 , 43 , 45 , 46 ]; two studies involved personnel during military training (one reporting “25% sufficient” and the other a mean of 78 μmol/L at baseline) [ 34 , 38 ]; two involved taekwondo (mean baseline of 31 nmol/L) [ 37 ] or swimmer athletes with mean levels of 60 μmol/L [ 31 ]; two studies involved either high school [ 47 ] or university students [ 33 ] where the baseline levels were not disclosed; and four studies involved children with mean baseline levels ranging from 30 to 67.5 nmol/L [ 32 , 35 , 40 , 48 ]. Vitamin D was administered in monthly doses at 200,000 tapering to 100,000 IU per month (provided by Tishcon) for up to approximately 1.6 years in two studies [ 29 , 42 ]; in weekly doses at 10,000 to 20,000 IU/week in five studies (provided by Dartnells, Dekristol, EuroPharm, Ddrops, or Tishcom) [ 32 , 33 , 36 , 40 , 46 ] with the longest study lasting five years [ 36 ]; the remaining eleven studies provided vitamin D in daily doses ranging from 400 IU per day for children [ 35 ], Japanese adults [ 45 ] and men during military training [ 38 ] to up to 5000 IU per day in male athletes with mean levels of 31 μmol/L at baseline [ 37 ], for a study duration up to one year (provided by Solgar, DSM, Pure Encapsulations, Minisun, BioTech, CTS Chemical, and Zenyaku) [ 30 , 31 , 34 , 35 , 37 , 38 , …”

“…They noted that vitamin D “reduced the severity of peak URTI symptoms by 15% [ p < 0.05]” and that participants beginning supplementation with serum levels below 50 μmol/L “had 21% lower peak severity”. This study did combine vitamin D supplementation and simulated sunlight groups together when reporting results but stated “no difference between these groups when combined” [ 34 ].…”

“…Three studies had data available for calculating a mean difference in days between those taking vitamin D vs. placebo, showing no difference in days with symptoms (MD days ranging from −0.80 to 0.10) with the largest non-significant effect in adolescent swimmers. [ 31 , 33 , 39 ] Harrison et al reported “Compared with placebo, vitamin D supplementation reduced the days with URTI by 36% ( p < 0.05); p < 0.05” [ 34 ] and Shimizu et al reported the median days duration was 10 days vs. 13 days for 400 IU/d compared to placebo, although not statistically significant ( p = 0.061) [ 45 ]. All other studies involving adults regardless of the amount or duration of taking vitamin D showed no change in duration of symptoms [ 42 , 43 , 46 ].…”