Vitamin A deficiency is a serious public health problem in most low- and middle-income countries, where it is the leading cause of childhood blindness and a major contributor to infectious disease morbidity and mortality.

Vitamin A supplementation as well as fortified foods are used to combat vitamin A deficiency. With multiple interventions, and vitamin A rich foods becoming more accessible, some population groups might even be at risk of getting too much vitamin A. Standard biomarkers of vitamin A status only measure deficiency, not excess.?