Vitamin D : Immunomodulatory Aspects

Vitamin D metabolites enhance immunity to a wide range of respiratory pathogens in vitro. Numerous observational studies have investigated whether vitamin D deficiency is a risk factor for acute respiratory infection, and a number of clinical trials of vitamin D supplementation for the prevention of acute respiratory infection have recently been conducted. Syntheses of this literature are lacking. We therefore conducted a systematic review of clinical studies investigating the association between vitamin D deficiency and susceptibility to acute respiratory infection in humans. A total of 39 studies (4 cross-sectional studies, 8 case-control studies, 13 cohort studies and 14 clinical trials) satisfying review eligibility criteria were identified. Observational studies predominantly reported statistically significant associations between low vitamin D status and increased risk of both upper and lower respiratory tract infections. Results from randomised controlled trials were conflicting however, reflecting heterogeneity in dosing regimens and baseline vitamin D status in study populations. Further trials of vitamin D supplementation for the prevention of acute respiratory infection should be conducted in populations with a high prevalence of vitamin D deficiency at baseline, using doses sufficient to induce sustained elevation of serum 25-hydroxyvitamin D concentrations, and powered to detect clinically important sub-group effects. This article is part of a Special Issue entitled 'Vitamin D Workshop'. Copyright © 2012 Elsevier Ltd. All rights reserved.

Objectives: To explore the effect of vitamin D supplementation in prevention of respiratory tract infections on the basis of published clinical trials. Materials and Methods: Clinical trials were searched from various electronic databases. Five clinical trials were suitable for inclusion. Outcome was events of respiratory tract infections in vitamin D group and placebo group. Data was reported as odds ratio with 95% confidence interval. Both random and fixed model was used for analysis. Analysis was done with the help of Comprehensive meta-analysis software 2. Results: Events of respiratory tract infections were significantly lower in vitamin D group as compared to control group [Odds ratio = 0.582 (0.417 – 0.812) P = 0.001] according to random model. Results were similar in fixed model. On separate analysis of clinical trials dealing with groups of children and adults, beneficial effect of vitamin D was observed in both, according to fixed model [Odds ratio = 0.579 (0.416 – 0.805), P = 0.001 and Odd ratio = 0.653 (0.472 – 0.9040, P = 0.010 respectively]. On using random model beneficial effect persisted in children's group but became nonsignificant in adults group [Odds ratio = 0.579 (0.416 – 0.805), P = 0.001 and Odd ratio = 0.544 (0.278 – 1.063) P = 0.075 respectively]. Conclusion: Vitamin D supplementation decreases the events related to respiratory tract infections. There is need of more well conducted clinical trials to reach to a certain conclusion.

Low serum 25-hydroxyvitamin D is a risk factor for osteoporosis, cardiovascular disease, diabetes, and cancer. Disruption of noncholesterol sterol absorption due to cholesterol-lowering therapies may result in reduced fat-soluble vitamin absorption. We have previously reported on the cholesterol-lowering efficacy and reduced sterol absorption of probiotic bile salt hydrolase active Lactobacillus reuteri NCIMB 30242; however, the effects on fat-soluble vitamins was previously unknown and the objective of the present study. DESIGN, SETTINGS, PATIENTS, AND INTERVENTION: The study was double-blind, placebo-controlled, randomized, parallel-arm, multicenter lasting 13 weeks. A total of 127 otherwise healthy hypercholesterolemic adults with low-density lipoprotein-cholesterol >3.4 mmol/L, triglycerides .05). L. reuteri NCIMB 30242 increased serum 25-hydroxyvitamin D by 14.9 nmol/L, or 25.5%, over the intervention period, which was a significant mean change relative to placebo of 17.1 nmol/L, or 22.4%, respectively (P = .003). To our knowledge, this is the first report of increased circulating 25-hydroxyvitamin D in response to oral probiotic supplementation.