Supplementing Vitamin D to Prevent Respiratory Infections in Children: A Recent Update

Abstract: The role of vitamin D (Vit D) in immune modulation and defence against respiratory infections has been the subject of intense discussion. Asthma, allergic rhinitis, and lower respiratory tract infections in children linked to wheezing are all strongly correlated with Vit D insufficiency. The anti-inflammatory and proinflammatory properties of Vit D are linked to immune tolerance. The improvement in defensins and cathelicidin expression mediates the anti-inflammatory effect. These compounds are particularly effective against gram-positive and gram-negative bacteria, as well as viruses, fungi, and bacteria, which are resistant to many medications. Enhanced autophagy, suppression of Th1 and Th17 cells, release of anti-inflammatory cytokines from Treg cells, and suppression of proliferation and immunoglobulin production from peripheral blood mononuclear cells can regulate autoimmunity in organs and allergic responses. Infants and children with respiratory tract infections frequently have low Vit D levels. The lack of sun exposure, physical exercise, Vit D intake, and seasonal changes, in addition to genetic predisposition of polymorphism in CYP27B1, are factors that impact 25(OH)D levels. The potential need for supplementation is inconclusive due to the heterogeneous nature of the studies. Serum Vit D level below 20 ng/mL has been shown to lead to a higher chance of developing respiratory infection in children. A preferred range of 40-60 ng/mL is recommended for protection against infection. Additionally, this protective effect may be more pronounced if vitamin D is administered daily or weekly as opposed to large, erratic amounts. This review describes recent updates on the association between Vit D deficiency and respiratory illness in children during acute infections.