To determine whether breast-feeding is protective against infection in
relatively affluent populations, morbidity data were collected by wee
kly monitoring during the first 2 years of life from matched cohorts o
f infants who were either breast fed (BF) (N = 46) or formula fed (FF)
(N = 41) until at least 12 months of age, Cohorts were matched for ch
aracteristics such as birth weight and parental socioeconomic status,
and we controlled for use of day care in data analysis, Mean maternal
educational level was high (16 years) in both groups, In the first yea
r of life the incidence of diarrheal illness among BF infants was half
that of FF: infants; the percentage with any otitis media was 19% low
er and with prolonged episodes (>10 days) was 80% lower in BF compared
with FF infants, There were no significant differences in rates of re
spiratory illness; nearly all cases were mild upper respiratory infect
ions, Morbidity rates did not differ significantly between groups in t
he second year of life, but the mean duration of episodes of otitis me
dia was longer in FF than BF infants (8.8 +/- 5.3 vs 5.9 +/- 3.5 days,
respectively; p = 0.01), These results indicate that the reduction in
morbidity associated with breast-feeding is of sufficient magnitude t
o be of public health significance.