Relationship Between Infant Feeding and Infectious Illness: A Prospective Study of Infants During the First Year of Life

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Abstract
Prior studies investigating the relationship between infant feeding and infectious illnesses in developed countries have provided conflicting data about whether breast-feeding protects against common infectious illnesses early in life. These conflicts may in part be due to the failure to consider the following methodologic issues: (1) collecting data prospectively at frequent intervals for active surveillance of the detection of infections and of feeding practices, (2) specifying what is meant by infectious illnesses and breast-feeding, (3) controlling for confounding variables such as social class or presence of siblings in the household, and (4) applying appropriate analytical strategies to a population in which both feeding and exposure to illness change over time. A total of 500 infants born consecutively in a university-affiliated community hospital in Copenhagen, Denmark, were studied prospectively for the first 12 months of life by means of a detailed, monthly, mailed questionnaire that focused on feeding practices and illnesses (overall response rate, 73%). The percentage of infants who were completely or mostly breast-fed decreased from 88% at 1 month to 20% at 12 months of age. After adjustment for major covariates, no statistically significant relationship was found between the type of infant feeding and the incidence of four categories of infectious illnesses: gastroenteritis, upper respiratory illness, otitis media, and lower respiratory illness. The adjusted incidence density ratio for gastroenteritis was 1.067 (95% confidence interval = 0.982, 1.226) and for upper respiratory illnesses 0.984 (95% confidence interval = 0.883, 1.096). These data suggest there is no substantial protective effect of breast-feeding against the occurrence of infectious illnesses early in life in a largely middle class urban population in a developed country.