Vitamin D and its Role in the Management and Prevention of Lower Respiratory Tract Infections in Infants and Young Children.

Lower respiratory tract infections are a major cause of mortality in children below the age of five years, particularly in resource-poor countries. Although advances in treatment protocols have reduced mortality rates, and improved vaccine technology has seen the development of more effective vaccines against a number of pathogens such as Streptococcus pneumoniae, the costs involved may prohibit their introduction in those countries most in need. Thus cheaper alternatives to boost infants’ and young children’s resistance to respiratory infections, and to reduce the severity of the disease when it occurs, are urgently needed. Over the last 20 years, the role of vitamin D in modulating the immune response to infection has generated considerable interest. The ability of vitamin D to enhance innate immunity through its role in stimulating the production of a number of antibacterial proteins, such as cathelicidin and defensins, and autophagosomes by activated monocytes and macrophages is well documented [1]. Vitamin D also has a role in adaptive immunity reducing the acute inflammatory response and increasing Th2 lymphocytes. A number of studies have highlighted the association between vitamin D deficiency/rickets and acute lower respiratory tract infections/pneumonia [2,3]; and in casecontrol studies, 25(OH)D levels have been found to be lower in cases with respiratory infections than controls [4], but it is unclear if improving the vitamin D status of infants will reduce the severity of the disease. Although it is possible that the observed association between rickets and pneumonia reflects the impaired immune response accompanying vitamin D deficiency, it is also possible that mechanical factors such as more pliable ribs associated with rickets and reduced ventilation and clearance of lung secretions due to hypotonia might play major roles.