Pregnancy and lactation: physiological adjustments, nutritional requirements and the role of dietary supplements.

Nutritional needs are increased during pregnancy and lactation for support of fetal and infant growth and development along with alterations in maternal tissues and metabolism. Total nutrient needs are not necessarily the sum of those accumulated in maternal tissues, products of pregnancy and lactation and those attributable to the maintenance of nonreproducing women. Maternal metabolism is adjusted through the elaboration of hormones that serve as mediators, redirecting nutrients to highly specialized maternal tissues specific to reproduction (i.e., placenta and mammary gland). It is most unlikely that the heightened nutrient needs for successful reproduction can always be met from the maternal diet. Requirements for energy-yielding macronutrients increase modestly compared with several micronutrients that are unevenly distributed among foods. Altered nutrient utilization and mobilization of reserves often offset enhanced needs but sometimes nutrient deficiencies are precipitated by reproduction. There are only limited data from well-controlled intervention studies with dietary supplements and with few exceptions (iron during pregnancy and folate during the periconceptional period), the evidence is not strong that nutrient supplements confer measurable benefit. More research is needed and in future studies attention must be given to subject characteristics that may influence ability to meet maternal and infant demands (genetic and environmental), nutrient-nutrient interactions, sensitivity and selectivity of measured outcomes and proper use of proxy measures. Consideration of these factors in future studies of pregnancy and lactation are necessary to provide an understanding of the links among maternal diet; nutritional supplementation; and fetal, infant and maternal health.