Breastfeeding is the gold standard and the body’s normal way to feed an infant. Pediatricians and nutritionists are unanimous in recommending that mothers exclusively breastfeed their infants for about six months. In its 2012 policy statement, the American Academy of Pediatrics reaffirmed this advice adding that complementary foods can be introduced at 6 months with the continuation of breastfeeding for one year or longer as mutually desired by the mother and infant. The World Health Organization also recommends exclusive breastfeeding for 6 months.
The advantages of exclusive breastfeeding for 3 months or more include significantly lower risks of respiratory tract and ear infections, asthma, bronchiolitis, atopic dermatitis, gastroenteritis, sudden infant death syndrome and several other diseases. Breastfeeding also confers greater protection against infections because it contains many immunological and protective factors. Human milk also promotes the maturation of the infant’s immune system. Other advantages of breastfeeding for 4 months or longer may include higher scores for fine motor skills and communication at age 3 compared with infants breastfed less than 4 months and higher academic achievement at 10 years of age, especially in boys. The American Academy of Pediatrics noted that the health benefits of breastfeeding are greater when the infant is fed longer than 3 months.
Evidence suggests that breastfeeding may have beneficial effects on the long-term health of the offspring, though not all studies are conclusive. Breastfeeding has been associated with a lower risk of developing insulin-dependent (Type 1) diabetes, metabolic syndrome, non-insulin-dependent (Type 2) diabetes, inflammatory bowel disease and a slightly lower risk of heart disease and stroke, although the risk of heart disease and stroke has not been confirmed by others. Children who were exposed to diabetes during fetal life had less fat tissue if they were breastfed for at least 6 months. There is also evidence that children and adolescents who were breastfed for at least 6 months were less likely to develop mental health problems. The links between breastfeeding and risks of allergic disease are inconsistent and vary with the type of allergy, family history of allergic disease and other factors. Environmental exposures, changes in gene expression, maternal and infant gene types, and various dietary factors have all been linked to the risk of allergy.
Whether breastfeeding partly protects against the development of overweight and obesity later in life is controversial. Several studies have confirmed that rapid growth in early infancy and weight are associated with being overweight and obese in childhood and adolescence. However, the evidence is inconclusive whether breastfeeding protects against the later development of being overweight and obese in the offspring. Breastfeeding is associated with a slower rate of weight gain in infancy and lower plasma insulin levels, which are associated with decreased fat storage. Faster infant growth and weight gain have been attributed to the higher protein content of infant formula compared with breast milk. Breastfeeding or formula with lower protein content restored the growth rate to that observed in breastfed infants. Others suggested that the higher energy density and volume of formula consumed contribute to the faster growth rate of formula-fed infants.
Until the development of fatty-acid-supplemented infant formula, breastfeeding was the only way to ensure that an infant received long-chain polyunsaturated fatty acids (PUFAs), including both docosahexaenoic acid (DHA) and arachidonic acid (ARA). Breast milk naturally contains both of these PUFAs, which are necessary for brain development and function, visual function, immune system development and other activities. DHA must be obtained from the diet in a preformed state because the usual Western diet provides too little from conversion of its fatty acid precursor alpha-linolenic acid or from body stores. Mothers who eat seafood regularly or take fish or algal oil supplements have higher levels of DHA in their breast milk than women who do not have dietary sources of these fatty acids. Women who do not eat fish, vegetarians and vegans, have lower levels of DHA in their breast milk compared with omnivore women or those who eat fish. Most, but not all, infant formulas now contain added DHA and arachidonic acid (ARA), an omega-6 fatty acid that also helps support infant development.
Are there any nutritional risks associated with exclusive breastfeeding for the first six months? Infants who are breastfed exclusively for 6 months may have a higher risk of developing iron-deficiency anemia compared with infants breastfed exclusively for less than six months. This danger can be overcome by ensuring that mothers consume enough iron during pregnancy and that complementary foods introduced into the infant’s diet contain iron. There is also concern that unsupplemented exclusively breastfed infants may be at high risk of vitamin D deficiency if they are not exposed to sunshine for at least 10 minutes, once a week. This risk may be greater in areas, such as parts of central and northern U.S., where sunlight exposure during winter is insufficient to trigger the production of vitamin D in the skin. However, vitamin D deficiency has been reported in unsupplemented, exclusively breastfed infants in sunny climates as well. The risk of vitamin D deficiency can be overcome with vitamin supplementation of the mother and infant. Mothers who are malnourished or have low nutrient status may put their infants at greater risk of nutrient shortfalls.
Infant formula feeding
Mothers may choose not to breastfeed their infant because of medical conditions, work-related issues, personal preferences, social and cultural perceptions, lack of appropriate support and other circumstances, but there are few medical reasons not to breastfeed. Mothers who decide not to breastfeed, regardless of the reason, can be reassured that their infant will be healthy, well nourished and have normal scores for growth and cognitive development. Many studies have demonstrated that infants consuming formula grow as well as breastfed infants and have comparable neurodevelopmental scores, without adverse effects.
Mothers who do not breastfeed have many choices among formulas. Brands differ by the source of protein(s) and the types of fat and carbohydrates they have. The main proteins are soy, various cow’s milk proteins or hydrolyzed proteins, which have been broken down to increase their digestibility. Some formulas are free of the sugar lactose. Most pediatricians recommend a formula with added iron to prevent anemia. Special formulas are available for preterm infants and those with medical needs. All infant formulas marketing in the U.S. must meet federal nutrient requirements and are regulated by the Food and Drug Administration.
Since 2001, infant formula manufacturers have been permitted to add two long-chain polyunsaturated fatty acids to their products. These are DHA and ARA. The amounts added are similar to the worldwide averages of these fatty acids that are found naturally in human milk. The addition of DHA and ARA ensures that the infant receives sufficient amounts of these fatty acids for healthy brain structure and function and visual development. The only DHA used in infant formula in the U.S. comes from a vegetarian and sustainable source, algae.
There is evidence showing that term or preterm infants supplemented with DHA in infancy may have improved visual acuity, attention and cognitive performance in childhood compared with infants fed unsupplemented formula, but results vary with the dose, time of assessment after birth and for cognition in particular, the measurement tool(s). Term infants fed different amounts of DHA with ARA had higher visual acuity scores at 12 months of age compared with those consuming the unsupplemented formula. The same study also reported that supplemented infants fed the lower doses of DHA with ARA spent longer processing an active stimulus than unsupplemented infants. In contrast to these reports, a meta-analysis of four large randomized trials concluded that DHA and ARA supplementation of infant formula had no clinically meaningful effect on infant neurodevelopment at 18 months as assessed with the Bayley Scales of Infant Development. Similarly, 1% DHA with ARA supplementation of preterm infants born at less than 33 weeks’ gestation was not associated with any effect on mental development scores on the Bayley Scales at 18 months, but scores were significantly higher among the DHA-supplemented girls. These authors also reported other benefits of high-dose DHA.
A concern with global cognitive tests measured at a single time point is their lack of sensitivity to the different developmental time courses for discrete cognitive functions. Thus, different aspects of cognition mature at different rates. A recent study showed that in infants whose scores did not differ on the Bayley Scales of cognitive performance at 18 months, exhibited positive effects of DHA and ARA supplementation at 3 to 6 years of age when assessed with a battery of cognitive tests at 36, 42, 48, 60 and 72 months of age. The results suggested that the benefits of DHA and ARA supplementation were observed in early measures of attention, preschool measures of rule learning and implementation and later measures of verbal ability. These findings suggest that more sophisticated measures of cognitive development over longer time may yield more information about the effects of DHA and ARA on cognitive development.
A referenced version of this backgrounder is available upon request from the editor.