| Vitamin A (VA) is an essential nutrient that is required for proper functioning of the visual system and cellular mechanisms that impact growth, epithelial integrity, reproduction, and immunity. If dietary intake is not sufficient to meet needs, tissues will not function optimally, and various health consequences result, including night blindness, total blindness, impaired immune function, anemia, and ultimately death. Economically disadvantaged populations, pregnant or lactating women, and young children are the most vulnerable to VA deficiency.;Dietary VA comes in two forms: preformed vitamin A found in animal products, fortificants, and supplements; and provitamin A carotenoids, found in orange and green fruits and vegetables. To reduce VA deficiency, numerous approaches have been implemented. Two of these are biofortification of staple or horticultural crops with provitamin A carotenoids and neonatal VA supplementation. Numerous staple and horticultural crops have been bred to increase provitamin A content. While the provitamin A carotenoid concentrations can be measured in the crop, human efficacy trials confirm that they can be absorbed and cleaved into VA when consumed by humans in a highly controlled setting. Next, effectiveness trials are needed to determine the impact of a biofortified crop once implemented in a less controlled setting.;Vital to any intervention evaluation is accurate assessment of VA status. Serum retinol, a traditional measurement, is not sensitive to VA status. Other more sensitive methods have been developed, and isotope dilution is currently considered the most sensitive, indirect measure of VA status across a wide range of VA stores. Estimation of VA stores by isotope dilution requires calculation from isotopic abundances, and the calculations required are being refined for different research applications.;Neonatal VA supplementation is under investigation as a strategy to reduce infant mortality. Due to conflicting results of mortality trials in humans, a review of the literature and a newborn piglet dosing study were undertaken to identify potential mechanisms, or lack thereof, of VA on infant survival. Primary outcomes were the absorption, transportation, storage, and metabolism of the VA dose given within the first few days of life. |
