Water-Soluble Vitamins in Human Milk Factors Affecting Their Concentration and Their Physiological Significance

Most B vitamins and vitamin C are among the nutrients in milk most strongly affected by maternal status and/or dietary intake. Recent analytical methods are more efficient and valid, revealing major differences in water-soluble vitamins across population groups. An inadequate supply in milk can be detrimental to the breastfed infant's health and development although cutoff points below which risk is increased are often uncertain, and little attention has been paid to adverse effects of low milk water-soluble vitamins on infant health and function. Concentrations change during lactation: thiamine, niacin, and pantothenic acid increase; B6, B12, and ascorbic acid gradually decrease; while riboflavin concentrations are stable, as is choline after an initial increase. Folate fluctuates until stabilizing in late lactation. Water-soluble vitamin concentrations in milk are also influenced by maternal supplementation, and, for some, by parity, preterm delivery, smoking, and maternal illness. However, there is relatively little change in concentrations during a feed nor is diurnal variation a major influence. Reported concentrations are used to set adequate intakes for infants and incremental requirements for lactation. However, the status of available data is poor due to the small number of participants in most studies, uncertainties about maternal nutritional status, and variable times of milk collection postpartum.