Issues and controversies with vitamin A in childhood.

Vitamin A deficiency is common in the developing world. Vitamin A supplementation (VAS) has been used to prevent or treat vitamin A deficiency and to decrease mortality and morbidity in children. However, there are still controversial issues in relation to the role of universal VAS in different populations. Thus, studies that look at mortality outcomes reveal that VAS decreases mortality in children >6 months of age; however, there is still controversy on the extent to which reduction in morbidity from diarrhea and respiratory infection, other than measles, decreases mortality. Studies in infants 1-5 months old show no protective effect of VAS on mortality; whether this is secondary to environmental influences (breastfeeding), or interactions with DTP vaccine, needs to be further investigated. Studies with VAS in newborns have resulted in contrasting results in countries in Africa and Asia; trials are underway to better understand this. VAS does not have a universal protective effect on lower respiratory tract infection in children; some studies reveal an increase in respiratory morbidity associated with VAS, especially in well-nourished children; in contrast, VAS may confer some protection to malnourished children. The interaction of VAS with different vaccines is under current debate; some discussions are presented.