Breast Feeding vs. Bottle Feeding --- Part II

In the First World, infant formula raises different but equally interesting issues. Like the WHO, the American Academy of Pediatrics (AAP) strongly supports breast-feeding. In a 1997 policy statement it declared that "breastfeeding ensures the best possible health as well as the best developmental and psychosocial outcomes for the infant." But the cohort born at the peak of formula-feeding, from 1946 to 1952, comprises the babies who started the boom, and they flourished, as the science writer Natalie Angier and others have reminded breast-feeding advocates. Yet whatever their present health --- could they not be even healthier? --- they did not necessarily have an easy time as babies.

Breast milk is an elaborate package of chemicals developed over millions of years of primate evolution to promote the newborn's development and build up its defenses against infection. Some of its constituent molecules keep microbes from spreading from the digestive tract into the body's tissues; others reduce the availability of vitamins and minerals (especially iron) that disease-causing bacteria need; and still others help the work of immune cells and kill bacteria directly by attacking their cell walls. And a variety of white blood cells helps the infant produce antibodies and attack microbes directly.

A pediatrician recalls how easily incorrect preparation of bottles by hospital formula rooms could caramelize the sugar and precipitate diarrhea. In fact, many infections are more common in bottle-fed infants deprived of the protective antibodies unique to mother's milk. Even now, pediatric researchers estimate that 250 to 300 infants die each year from diarrheal infections as a result of bottle-feeding; another 500 to 600 die from respiratory diseases. Middle ear infections, more frequent among formula-fed children, have been treatable with antibiotics, but the high price of therapy has included the rise of resistant strains of bacteria.

Even more important and less well known is how formula-feeding affects the long-term welfare of both infants and mothers. Whether to breast-feed or bottle-feed has always been a cultural as well as a biological decision. Mothers who choose one or the other method may well feed their children differently after weaning, give them more or less encouragement in school. They may be more or less affluent than other parents, and their children may have different peers and experiences. Bottle-fed infants are also more likely to be given pacifiers, which in turn differ in design and in their effects on the development of the mouth.

Despite all these possible biases there is evidence --- sometimes limited and controversial --- of long-term benefits of breast-feeding. Breast-fed children may develop slightly higher intelligence than bottle-fed contemporaries. A number of chemicals that appear in human milk but not in formula, including arachidonic acid (AA) and docosahexaenoic acid (DHA), are known to promote brain growth. Longer-term breast-feeding has been linked in one study to faster motor and cognitive development.In another, premature infants tube-fed with human milk had an 8.3-point IQ advantage over their formula-fed counterparts at the age of seven and a half --- this after downward adjustment to reflect their mothers' educational and social status. Some studies show only weak or insignificant gains after adjustment for family background, but the very first study of feeding method and mental development, published in 1929, showed advantages for breast-feeding at a time when formula-feeding was chic and breast-feeding associated with immigrants and the working class.

The immune system also may be affected by infant feeding. The nutrition researcher Alan Lucas has pointed out that studies of other animals show effects of prenatal and postnatal nutrition on indicators of health from size and metabolism to obesity, hardening of the arteries, and longevity. There is evidence, if not yet proof, that there are critical periods in human development, "programming windows" for stimuli that enable or inhibit later behavior. Very early in their lives, chicks, mallard ducklings, and some infant mammals become attached to the first thing they encounter, in nature nearly always a parent but in the laboratory sometimes a human being, another animal, or even an object.

Since the 1960s, scientists have been able to produce lifelong changes with brief early interventions; rats receiving less nourishment in their first three weeks remain smaller than others. Baboons overfed in infancy gain weight in early adulthood as though by a delayed causal mechanism. Lucas believes nutritional programming may have effects on human health.

Are we not only what we eat, but what we ate? Fragmentary but intriguing evidence exists. Inflammatory bowel diseases may be linked to very early nutrition. Studies have shown that ulcerative colitis and Crohn's disease (a chronic inflammatory disease of the intestines) are less common among those raised on breast milk. Another study suggests that artificial feeding has been responsible for the long-term increase in juvenile diabetes; the authors attribute a quarter of all cases to bottle-feeding. Because childhood infections of the ear and the lower respiratory tract may lead to chronic respiratory illness, the early benefits of breast-feeding can carry through to later life.

There are also indications that breast milk may reduce the risk of malignant lymphomas, multiple sclerosis, and coronary artery disease. Exclusive breast-feeding for at least four months after birth has been shown to reduce the risk of childhood asthma significantly. The number of studies in each case is small, and breast-feeding advocates in medicine also acknowledge that human milk is no panacea; it probably only delays the onset of allergies, for example. But the studies have still contributed to medical organizations' overwhelming support for extended breast-feeding.

Industrial and postindustrial culture also affects the timing of feeding. For most of human history, there was no supplementary feeding, and infants were allowed access to milk frequently, with short intervals between feeds. Most of today's breast-feeding mothers, especially in economically advanced nations, nourish their infants fewer times each day. The original style is healthier for babies, helps prevent jaundice, and it's less likely that overenthusiastic sucking by hungry infants will cause the mother pain. While the standard U.S. breast-feeding handbook now recommends nursing "at least every two or three hours," this is not feasible for many employed mothers, though their stored milk may be fed to their infants by sitters.

Breast-feeding may also protect mothers in ways that are not fully understood because our culture --- even among most breast-feeding mothers --- departs from many of the patterns present during the evolution of our species. Katherine Dettwyler has argued persuasively that human infants follow a "hominid blueprint" for extended nursing. Studies of other living primate species have established a formula linking weight at maturity to age of weaning. For human weight, the formula predicts, conservatively, a natural age of weaning of from 2.8 to 3.7 years, varying with adult female weight. Studies of gestation time and weaning suggest that in humans, as in chimpanzees and gorillas, breast-feeding would last at least six times as long as gestation rather than for nine months, as many medical texts assert.

Other primate studies link weaning strongly with the eruption of the first permanent molar; this happens to human children, regardless of nutritional status, at the age of 5.5 to 6 years, about the time they acquire adult immune competence. Thus infants are biologically inclined to continue nursing until their third or fourth year or even longer. Katherine Dettwyler believes there may be benefits for both mothers and infants in prolonged lactation; she cites research that suggests that small but significant numbers of mothers in industrial societies continue suckling their children discreetly well beyond the second and third year. Indeed, in 1999 a Chicago newspaper found a local four-year-old preschooler with his own computer who scandalized guests at a parental party by taking such a milk break, raising his fists "Muhammad Ali-style, and declaring, 'That was sooooo good."'

And despite the reservations of some psychologists, there seem to be no physical or mental ill effects among late-nursing children. One of them in Chicago grew up to be a massive offensive linesman at Texas A&M who says he has not been sick since eighth grade and has no memories of nursing.

Because this ancient pattern of breast-feeding is difficult to study in Western societies, we still are not sure of its effects on maternal health. There is some evidence that prolonged breast-feeding has protective value against breast cancer, especially among premenopausal women. Societies in which breast-feeding is widespread tend to have lower rates of breast cancer, and when infants are fed unilaterally, the suckled breast is significantly less likely to develop cancer. Breast-feeding is also thought to reduce ovarian and endometrial cancer. Since the choice of whether to bottle-feed or breast-feed may be associated with so many differences in diet and other practices, these findings are more suggestive than conclusive. But it still seems likely that future clinical studies will confirm some significant long-term differences in the health of breast-feeding and bottle-feeding women.