Impact of maternal nutritional status on human milk quality and infant outcomes: an update on key nutrients.

The profound importance of human milk in optimizing neonatal health and improving child survival is becoming increasingly more apparent, both domestically (1–5) and internationally (6). Human milk is recommended as the sole source of nutrition for the first 6 mo of life (7–10) and is an important food source for the first 1 (7) to 2 y (11). Therefore, promoting and protecting human milk nutrient quality are of great public health concern. Until recently, it was widely believed that nutritional deficiencies in breast-fed infants were relatively rare. Routine supplementation of breast-fed infants is not recommended in the United States, with the exception of vitamin K in the newly delivered neonate (12) and—since 2005—vitamin D supplementation throughout infancy (13). However, WHO expert consultation on the optimal duration of exclusive breastfeeding (10) did acknowledge that data are insufficient to exclude the possibility of micronutrient deficiencies in some infants exclusively breastfed for 6 mo. Thus, there has been a renewed effort to better understand the relationship between maternal micronutrient status and human milk quality, particularly in regions of the world where diet quality is poor (14). However, even for women in resource-rich settings, modern trends in diet and lifestyle may compromise human milk nutrient levels. For example, it was previously believed that only strict vegans were at risk of vitamin B-12 deficiency. However, recent studies have revealed that even lacto-ovo vegetarians and individuals who consume low amounts of meat (15) are at greater risk of vitamin B-12 deficiency compared with those consuming larger amounts of meat. Furthermore, current public health recommendations advise pregnant and lactating women to limit their consumption of seafood with high methylmercury levels (16) and for all individuals to minimize sun exposure, practices that may compromise the levels of (n-3) fatty acids (17) and vitamin D (18) in human milk, respectively. These contemporary issues highlight the need to better understand the impact of maternal dietary intake on human milk nutrient levels and the resultant infant functional outcomes. For some nutrients, the answers to these relationships are relatively well established; however, important knowledge gaps remain in our understanding of these relationships for select nutrients. Our expert panel was invited to address the current evidence and summarize emerging research with regard to human milk quality, focusing on the B vitamins, vitamin D, and docosahexaenoic acid (DHA). Dr. Lindsay Allen (19) presents a global overview of B vitamin levels in human milk, how these levels are influenced by maternal diet and supplementation patterns, and the B vitamin status of infants breast-fed by mothers with inadequate B vitamin intake. Drs. Adekunle Dawodu and Reginald Tsang (20) provide an overview of the interplay between the vitamin D status of the mother, her milk, and her infant in a contemporary, cross-national context. Their paper also highlights intriguing recent research evaluating maternal vitamin D supplementation as a means to improve the vitamin D status of infants in settings with very low maternal vitamin D levels. Dr. Christina Valentine (21) presents a critical review of the literature addressing the relationship between maternal DHA intake and DHA levels in human milk, including the donor milk supply in the United States and the potential impact of human milk DHA content on functional outcomes in the preterm infant. Although each of these authors has focused on addressing suboptimal human milk levels of select nutrients, these symposium proceedings should not be interpreted as reasons to disregard current recommendations to provide human milk as the sole source of nutrition for the first 6 mo of life. On the contrary, all 4 authors acknowledge the vitally important nutritional and immunological advantages of exclusive breastfeeding. In the instances in which human milk nutrient levels have been shown to be suboptimal, each author has highlighted emerging research on interventions designed to address the problem, primarily by improving maternal intake. It would be misguided to “solve” the problem of a nutrient deficiency in human milk by recommending human milk substitutes because this ignores the importance of exclusive breastfeeding in maximizing protection from infectious disease and improving child survival. By tackling the issue of human milk quality for select nutrients, this symposium provides a road map for future research focused on protecting and promoting human milk quality. Clearly, more research is needed to determine the safety and effectiveness of approaches used to address this challenging public health issue.