In this 400-page report, prepared for the Agency for Healthcare Research and Quality, the authors evaluate studies of the effects or associations of breastfeeding on various child and maternal outcomes. In a screening of over 9,000 abstracts, researchers from the Tufts-New England Medical Center Evidence-Based Practice Center identified 43 primary studies on infant health outcomes, 43 primary studies on maternal health outcomes, and 29 systematic reviews or meta-analyses to be included in the review. The primary studies were observational, randomized controlled trials, and comparative studies. The systematic reviews were included since it was not deemed feasible for all of the primary studies to be reviewed. The authors relied on the recommendations of the technical expert panel and the Office on Women’s Health to develop an approach to grade the reviews. This approach graded the meta-analyses and the primary studies included in the review as A for good, B for fair to moderate, and C for poor. “A” studies presented the least bias and the most valid results. “B” studies were susceptible to some bias but were still considered valid, and the “C” studies had significant biases that may have resulted in invalid results. In addition, screening for the meta-analyses and systematic reviews included standards for reporting for meta-analysis in observational studies in epidemiology and a checklist developed specifically for this review to evaluate the quality of the reviews of observational studies. The checklist included such questions as whether the study included an appropriate search strategy, justification for inclusion/exclusion criteria for studies, and a description of a well-defined population.
The inclusion criteria required studies to have a comparative arm of formula feeding or different durations of breastfeeding, and studies had to have been conducted in developed countries. For topics that included the systematic reviews/meta-analyses, any additional primary studies were reviewed if they were published subsequent to those reviews. Studies that only included formula-fed infants were not included in the review.
Definition of breastfeeding was varied across studies reviewed, so the authors elected to use the definition of exclusive breastfeeding as provided by the authors of the studies reviewed and to qualify the conclusions based on these definitions. Data were presented as a reduction in relative risk, estimated as (1–odds ratio) x 100%, along with the corresponding 95% confidence interval (CI).
For the full-term infant, breastfeeding was associated with a reduced risk of acute otitis media, atopic dermatitis, gastrointestinal infections, lower respiratory tract diseases, asthma, obesity, childhood leukemia, and sudden infant death syndrome. There was a 23% (95% CI, 9–36%) reduction of otitis media when breastfeeding was compared to exclusive formula feeding. When exclusive breastfeeding for three or six months’ duration was compared to exclusive formula feeding, there was a reduction of otitis media of 50%...