Maternal Vitamin D Supplementation for the Prevention of Respiratory Tract Infections in Offspring: A Meta-Analysis

Maternal vitamin D intakes during pregnancy and child health outcome

We conducted a follow up of the children in Mongolia whose mothers received one of the three doses of vitamin D (600, 2000, or 4000 IU daily) during pregnancy as part of the randomized, double-blind, clinical trial of vitamin D supplementation to determine their impact on child health to two years. In the parental trial, 119 pregnant women were assigned to 600 IU/day, 121 were assigned 2000 IU/day, and 120 were assigned 4000 IU/day starting at 12-16 weeks' gestation and continuing throughout pregnancy. At baseline, maternal serum 25(OH)D concentrations were similar across arms; 91 % were 50 nmol/l. As expected, there was a dose-response association between the amount of vitamin D consumed (600, 2000, or 4000 IU daily) and maternal 25(OH)D levels at the end of the intervention. Total 311 children of 311 mothers were followed for 2 years to evaluate health outcomes. We determined the child's health outcomes (rickets, respiratory disease [pneumonia, asthma], and diarrhea/vomiting) using a questionnaire and physical examination (3, 6, and 24 months of age). Low levels of mothers' serum 25(OH)D during pregnancy increased the risk of developing rickets, respiratory illness, and other diseases in children during the early childhood period. Rickets was diagnosed in 15.6 % of children of women who received 600 IU of vitamin D during pregnancy, which was higher than in other vitamin D groups. Children in the group whose mothers received low doses of vitamin D (600 IU/day) had a greater probability of developing respiratory diseases compared to the other groups: pneumonia was diagnosed in n = 36 (35.0 %) which was significantly higher than the group receiving vitamin D 4000 IU/day (n = 34 (31.5 %) p = 0.048). In the group whose pregnant mother consumed 600 IU/day of vitamin D, the risk of child pneumonia was ∼ 2 times higher than in the group who consumed 4000 IU/day (OR=1.99, 95 % CI: 1.01-3.90). The incidence of diarrhea and vomiting in children was 12.1 % lower in the 2000 IU/day group and 13.1 % lower in the 4000 IU/day group compared with the 600 IU/day group (p = 0.051). The offspring of pregnant women who regularly used vitamin D at doses above 600 IU/day had lower respiratory disease, rickets, and diarrheal risks at 2 years.

The Effects of Vitamin D Supplementation on Respiratory Infections in Children under 6 Years Old: A Systematic Review

Childhood respiratory tract infections (RTIs) pose a significant health burden, especially in children under six years old. The main objective of this systematic review was to assess the effectiveness of vitamin D supplementation in the prevention of RTI in this population while also exploring potential effect modifiers such as age, baseline vitamin D status, and type of respiratory infection. A systematic review of the literature published up to February 2023 was conducted according to PRISMA guidelines, searching PubMed, Web of Science, Cochrane, and Scopus databases. Eight studies met the inclusion criteria, which investigated the association between vitamin D supplementation and respiratory infections in children between zero and five years old. The included studies were conducted between 2012 and 2021, encompassing a total of 2189 children from five randomized trials, two case-control studies, and one prospective cohort study. The relationship between vitamin D supplementation and the prevention of childhood RTI was not consistently observed across all included studies. Pooled results demonstrated varied effects of vitamin D supplementation on respiratory infection incidence, severity, and symptoms. Three studies reported statistically significant associations between low vitamin D levels and respiratory infections (OR = 4.90, OR = 6.97), while one study found that children who received vitamin D supplementation of 800 UI/day for 3 months during the cold season had fewer episodes of respiratory symptoms (RR = 0.55) and recovered more quickly from acute RTI. Lastly, according to one study, vitamin D intake < 80 IU/kg/day was significantly associated with the risk of acquiring pneumonia (OR 7.9) but not bronchiolitis. The remaining five studies found no statistically significant differences in infection rates or severity (p-value > 0.050). The available evidence on the effectiveness of vitamin D supplementation for preventing and treating respiratory infections in children under six years old is limited, with only a few favorable effects being reported. In some cases, a dose of 80 UI/kg/day was found to provide significant protection for acute respiratory infections, although in the major trials the only benefit was a quicker recovery and fewer respiratory symptoms, with no impact on incidence and severity of respiratory infections. Nevertheless, the study protocol, the supplementation dose, and duration of supplementation had significant variations between studies, leading to inconclusive findings.