Many population groups in the developing world suffer from multiple nutrient deficiencies. The clustering of iron and vitamin A deficiencies has already been mentioned, but there are many more significant overlaps.

Moreover, deficiencies often interact. Vitamin A supplementation at appropriate levels has been found to improve not only vitamin A status but also iron metabolism in pregnant women and preschool and school-age children.²⁸ It should be considered where iron deficiency is common. A combined iron and vitamin A supplement has been found to be more than 40% more effective in reducing anaemia than an iron supplement alone. Such findings are not specific to supplementation. A vitamin A sugar fortification programme in Guatemala resulted in improved iron status of the population,²⁹ while a trial with vitamin A - fortified MSG in Indonesia increased haemoglobin levels among children.³⁰

Given such frequent overlaps and given the fact that at certain stages of the life cycle - most notably during pregnancy - it may be difficult for dietary needs to be met through diet alone, multiple micro-nutrient supplementation holds clear potential to address multiple nutrient deficiencies in a cost-effective manner. Recent advances have been made in this area since 1998. One publication has addressed key issues concerning the design and implementation of such programmes.³¹ Also, a joint UNICEF/WHO/UNU workshop was convened in 1999 to consider the composition of a multi-micronutrient supplement to be used in forthcoming trials among pregnant women in developing countries.