Diet-related micronutrient deficiencies rarely occur in isolation; deficiencies of iodine and vitamin A or of iron and vitamin A or zinc are often observed in the same populations. In addition, widespread deficiencies of some micronutrients, for example, zinc and calcium, may often go undiagnosed because of the absence of specific and sensitive status indicators. Multiple micronutrient supplementation can be more effective in improving nutritional status than supplementation with single key micronutrients; therefore, the multiple fortification of appropriate food vectors, including beverages, is of interest from the nutritional standpoint. Beverages fortified with multiple micronutrients include dairy products, chocolate beverages, fruit juices, and soya-based drinks. As well as the documented or estimated micronutrient deficiencies and the requirements of the target population or consumer group, the conception of such a multiply fortified beverage must take into account a number of other important factors. The choice of the chemical form of the fortification micronutrients should be made with consideration of bioavailability, the effects on the organoleptic characteristics of the particular beverage, and cost. The initial calculation of the composition of the micronutrient premix should include the levels of micronutrients in the raw materials used and the estimated losses of specific micronutrients during processing and storage. Preliminary production and storage trials are then needed to determine the actual losses. The composition of the micronutrient premix may then be finalized. Interactions, both positive and negative, between fortification micronutrients may also need to be considered. For example, the bioavailability of iron may be enhanced by the addition of vitamin C, whereas mineral–vitamin and vitamin–vitamin interactions can accelerate the destruction of some vitamins. To render quality control procedures simple and cost-effective, only a limited number of fortification micronutrients, which are especially sensitive to losses and which are easy to measure, may be analysed. Simple, inexpensive, and rigorous analytical methods for such measurements are now available.
Impact of vitamin A transport and storage on intestinal retinoid homeostasis and functions
