Return to table of contents

BREAST MILK AND ALLERGIES: PROPHYLAXIS OR RISK?

PERTH, AUSTRALIA-The nutritional superiority of breast milk over formula is well established, but another long-debated question--does breast-feeding prevent allergy and asthma?--has yet to be resolved. Or has it been? A recent study from Australia suggested that breast-feeding for at least 4 months after birth does protect against childhood asthma.¹

Wendy H. Oddy, MD, of the Institute for Child Health Research in Perth, Western Australia, and her colleagues prospectively followed 2,187 children from birth until age 6 years to determine whether there was a link between breast-feeding and asthma and allergies. She found that breast-feeding for more than 4 months was associated with a substantial reduction in the risk of asthma at age 6 years.

In contrast, longitudinal data collected by the Tucson Children's Respiratory Study and presented at the American Lung Association/American Thoracic Society International Conference in San Diego,² showed that breast-feeding did not affect the prevalence of childhood asthma--although in a subgroup analysis of mothers with asthma, breast-fed children showed a significantly increased risk of developing asthma. However, the authors emphasized the preliminary nature of their findings, which will, they said, require confirmation. They also indicated that this potential association (between asthmatic mothers who breast-feed and increased risk of asthma in their children) should not lead clinicians to advise asthmatic mothers against breast-feeding. Breast milk has many other proven benefits. As Anne L. Wright, PhD, lead author of the Tucson Study and a Research Professor, Department of Pediatrics and Respiratory Sciences Center, University of Arizona, Tucson, told Respiratory Reviews, "It's important to look at the clinical implications of this and not just at some marker in the blood." Dr. Wright is also lead author of a paper based on those longitudinal data and published in a recent issue of the Journal of Allergy and Clinical Immunology.³

In that study, which examined the relationship of breast-feeding, maternal IgE, and total serum IgE in childhood, Dr. Wright and colleagues noted the "controversy regarding the relationship of the effect of breast-feeding on markers of allergy such as total serum IgE in childhood." While the study showed a relationship with the mother's IgE, it showed no relation with the father's IgE levels.

The Tucson study measured total serum IgE at four ages (birth, 9 months, 6 years, and 11 years) in unselected children enrolled in the study at birth. Total serum IgE level is a marker of allergic response, clearly associated with allergic symptoms in childhood, atopy, asthma, and bronchial hyperresponsiveness. IgE is also implicated in the pathogenesis of allergic asthma. On the basis of a physician report or parent questionnaires completed when the child was age 18 months, the children were classified as never breast-fed, breast-fed for less than 4 months, and breast-fed for 4 months or longer.

Among children whose mothers were in the two lower tertiles of IgE, breast-feeding was associated with lower total serum IgE at age 6 years (24.2 vs 44.3 IU/mL for never--breast-fed children, P < .02). However, in children whose mothers were in the highest tertile of IgE, breast-feeding for at least 4 months was associated with higher IgE levels compared with those never breast-fed (by highest tertile mothers) or breast-fed for less than 4 months (97 vs 38.9 IU/mL, P<.005).

The investigators suggested several possible explanations for what they term the "paradoxic relationship" of mother and child IgE levels. "First, it is possible that some aspect of the shared environment of both mothers with high IgE levels and their children might swamp the beneficial effects of breast-feeding seen in the low--<\#029>maternal IgE group." However, in Tucson, sensitization is most commonly seen in relation to aeroallergens and ubiquitous molds rather than to indoor and other localized allergens.

A second possibility is that milk produced by allergic mothers might differ in some significant, but as yet undetermined, ways from that of nonallergic mothers. Thirdly, because cytokines play a crucial role in the regulation of IgE synthesis, those substances might differ by maternal atopic status and might possibly affect development of the immune system markers of allergy in the child. Or it may be that breast-feeding alters some other outcome affecting IgE production.

"Environmental exposures in the early months of life are critical for the development of the immune system but have the potential to predispose to allergy or atopy," note Dr. Oddy and colleagues. "Breast-feeding may be an important part of the immune response, but whether breast-feeding protects against asthma or atopy, or both, is controversial."

The Western Australian pregnancy cohort study is a prospective birth cohort initially established (1989-1992) as a randomized clinical trial, which indicated that multiple ultrasonography did not improve pregnancy outcome. A total of 2,602 (91%) of the original cohort (of infants) remained available for follow-up at 6 years; 2,187 were assessed for the link between breast-feeding and asthma and other allergies. Definitions of asthma included physician-diagnosed asthma and wheeze 3 or more times a year since age 1, wheeze in the past year, sleep disturbance due to wheeze in the past year, and atopy established by a prick test.

At enrollment, parents completed a questionnaire about the child's general health. Parents also kept a diary of their child's health during the first year of life. When the child was age 1 year, the parents completed a questionnaire that included items about feeding. At about age 6 years, the parents were contacted and sent another questionnaire that included items about smoking in the household, family history of respiratory symptoms, and illnesses in the study child.

After adjusting for other possible contributors such as low birth weight, premature birth, and maternal smoking, the investigators found that feeding infants milk other than breast milk before they were age 4 months led to an increase in asthma cases. The odds ratio for asthma diagnosis was 1.25; for wheeze three or more times since age 1 year, 1.41; for wheeze in the past year, 1.31; and for sleep disturbance due to wheeze within the past year, 1.4.

"This protective effect [of breast-feeding] may work through several mechanisms," the authors explained. "These include the exclusion of milk other than breast milk (and its potentially allergenic components) from the diet; and the provision of immunomodulatory, anti-inflammatory, nutritional or other components in human milk." The researchers found that it was the age at which breast-feeding ceased and other milk was introduced--rather than the duration of breast-feeding itself--which was more closely associated with a diagnosis of asthma at age 6 years, a fact favoring the "exclusion" mechanism.

-Margaret A. Inman

References
1. Oddy WH, Holt PG, Sly PD, et al. Association between breast feeding and asthma in 6 year old children: findings of a prospective birth cohort study. BMJ. 1999;319:815-819.
2. Wright AL, Halonen M, Holberg CJ, et al. Breastfeeding and maternal asthma alter risk of childhood asthma. Paper presented at: ALA/ATS International Conference; April 25-28,1999; San Diego, Calif.
3. Wright AL, Sherrill D, Holberg CJ, et al. Breast-feeding, maternal IgE, and total serum IgE in childhood. J Allergy Clin Immunol. 1999;104(3 pt 1):589-594.

Return to table of contents