Infant colic: empirical evidence of the absence of an association with source of early infant nutrition.

Background: The etiology of infant colic remains unknown, despite an abundance of research on the topic.

Objective: To determine whether breastfeeding has a protective effect in colic's development.

Design: A prospective cohort study of 856 mother-infant dyads. Eligible participants included English-speaking adult residents of a region in Ontario, who gave birth, at term, to a live singleton whose birth weight was appropriate for gestational age. Self-administered questionnaires, mailed to mothers at 1 and 6 weeks post partum, requested information on several infant and maternal factors, including source of infant nutrition (exclusively breastfed, complementary fed, and exclusively formula fed). Cases of colic were identified by applying modified Wessel criteria to data recorded in the Barr Baby Day Diary or by interpreting responses to the Ames Cry Score.

Main Outcome Measures: Prevalence of colic among breastfed, formula-fed, and complementary-fed infants; and adjusted odds ratios (AORs) reflecting the prevalence of colic among formula- and complementary-fed infants relative to those who were breastfed.

Results: Of 856 mothers, 733 (86%) completed the first questionnaire and 617 (72%) completed the second questionnaire. Overall, the prevalence of colic at 6 weeks was 24%. No association was seen between the source of infant nutrition and colic's development. In multivariate analyses, higher levels of maternal trait anxiety (AOR, 1.22; 95% confidence interval [CI], 0.96-1.54), maternal alcohol consumption at 6 weeks (AOR, 1.57; 95% CI, 1.03-2.40), and shift work during pregnancy (AOR, 1.27; 95% CI, 0.73-2.21) were associated with an increased likelihood of colic, after controlling for feeding method, maternal age, and parity. In these same analyses, being married or having a common-law partner (AOR, 0.30; 95% CI, 0.10-0.87) and being employed full-time during pregnancy (AOR, 0.60; 95% CI, 0.32-1.14) were associated with a reduced likelihood of colic.

Conclusions: Breastfeeding did not have a protective effect on the development of colic. Although colic was statistically associated with several variables, including preexisting maternal anxiety, much of colic's etiology remains unexplained.