Vitamin A in pregnancy: requirements and safety limits

Most of the functions of vitamin A are mediated through the binding of reti noic acid to specific nuclear receptors that regulate genomic expression. R ecent experimental work in transgenic mice showed clearly that normal embry onic development depends on the correct spatial and temporal expression of the receptors in the differentiating cells and on the binding of specific f orms of retinoic acid. This implies that the parent compound, vitamin A, is available in adequate forms and quantities. Excessive dietary intake of vi tamin A has been associated with teratogenicity in humans in <20 reported c ases over 30 y. However, caution must be exercised to avoid unnecessary sup plementation of women of childbearing age. Hypovitaminosis A affects millio ns of women and children worldwide. The main consequence of a poor vitamin A supply during pregnancy is a low vitamins status at birth and in the next few months. Vitamin A deficiency is strongly associated with depressed imm une function and higher morbidity and mortality due to infectious diseases such as diarrhea, measles, and respiratory infections. Vitamin A deficiency is often associated with an increased mother-to-child transmission of HIV- 1. The initiation of vitamin A supplementation should be carefully examined in each case according to the risk-to-benefit ratio. The final decision sh ould take into account the estimated vitamin A status of the woman, the ava ilability of vitamin A-rich foods in her diet, and whether supplementation can be supervised.