A Cochrane review [Abstract] 1 included 23 studies with a total of 9666 subjects. Eleven studies were from developing countries (2 controlled trials), and 12 from developed countries (all observational studies). Definitions of exclusive breastfeeding varied considerably across studies. Trials and the observational studies suggest that infants who continue to be exclusively breastfed for six months show no deficits in weight or length gain, although larger sample sizes would be required to rule out modest differences in risk of undernutrition. In developing country settings where newborn iron stores may be suboptimal, exclusive breastfeeding without iron supplementatin may compromise haematologic status. Infants who continue exclusive breastfeeding for six months or more appear to have a reduced risk of gastrointestinal or respiratory infection. No significant reduction in risk of atopic eczema, asthma or other atopic outcomes has been demonstrated. The mothers had longer lactational amenorrhoea and more rapid postpartum weight loss.
A trial 2 in the UK randomly assigned 1303 exclusively breast-fed infants who were 3 months of age to early or late introduction of 6 allergenic foods (peanut, cooked egg, cow's milk, sesame, whitefish, and wheat; early-introduction at 3 months or standard-introduction at 6 months of age). The primary outcome was food allergy to one or more of the 6 foods between 1 year and 3 years of age.In the intention-to-treat analysis, food allergy developed in 7.1% in the standard-introduction group (42/ 595 participants) and in 5.6% in the early-introduction group (32/ 567) (P=0.32). In the per-protocol analysis, the prevalence of any food allergy was significantly lower in the early-introduction group than in the standard-introduction group (2.4% vs. 7.3%, P=0.01), as was the prevalence of peanut allergy (0% vs. 2.5%, P=0.003) and egg allergy (1.4% vs. 5.5%, P=0.009); there were no significant effects with respect to milk, sesame, fish, or wheat. The consumption of 2 g per week of peanut or egg-white protein was associated with a significantly lower prevalence of these respective allergies than was less consumption. Drop-out rate of infants recruited in the early group was 69.1%.
Another trial 3 randomly assigned 640 infants with severe eczema, egg allergy, or both to consume or avoid peanuts until 60 months of age. Participants, who were at least 4 months but younger than 11 months of age at randomization, were assigned to separate study cohorts on the basis of pre-existing sensitivity to peanut extract, which was determined with the use of a skin-prick test--one consisting of participants with no measurable wheal after testing and the other consisting of those with a wheal measuring 1 to 4 mm in diameter. Among the 530 infants in the intention-to-treat population who initially had negative results on the skin-prick test, the prevalence of peanut allergy at 60 months of age was 13.7% in the avoidance group and 1.9% in the consumption group (P<0.001). Among the 98 participants in the intention-to-treat population who initially had positive test results, the prevalence of peanut allergy was 35.3% in the avoidance group and 10.6% in the consumption group (P=0.004). There was no significant between-group difference in the incidence of serious adverse events.
Yet another controlled trial 4 randomized 319 high-risk infants (with at least 1 first-degree relative with allergic disease and a skin prick test response to egg white) at age 4 months to receive whole-egg powder or placebo (rice powder) until 8 months of age, with all other dietary egg excluded. The primary outcome was an eggwhite skin prick test response of 3 mm or greater at age 12 months.14 infants reacted to egg within 1 week of introduction and were excluded. 253 (83%) infants were assessed at 12 months of age. Loss to follow-up was similar between groups. Sensitization to egg white at 12 months was 20% and 11% in infants randomized to placebo and egg, respectively (odds ratio, 0.46; 95% CI 0.22 to 0.95; P = .03). The absolute risk reduction was 9.8% (95% CI, 8.2% to 18.9%), with a number needed to treat of 11 (95% CI, 6 to 122). Levels of IgG4 to egg proteins and IgG4/IgE ratios were higher in those randomized to egg (P < .0001 for each) at 12 months. There was no effect on the proportion of children with probable egg allergy (placebo, 13; egg, 8).
Comment: The quality of evidence is downgraded by study quality.
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