All day-long pacifier use and intelligence quotient in childhood: A birth cohort study.

BACKGROUND Literature on pacifier use remains controversial, but mostly suggests an inverse association with childhood intelligence. OBJECTIVES The objective of this study was to assess the association between pacifier use and intelligence quotient (IQ) in six-year-old children from a birth cohort. METHODS Data from 3532 children from the 2004 Pelotas (Brazil) Birth Cohort were analysed. Children were recruited and assessed at birth and followed up at 3 months, and 1, 2, 4, and 6 years. Data on pacifier use duration and intensity were obtained via interviews with mothers in all six follow-up visits. IQ was estimated at 6 years using the Wechsler Intelligence Scale for Children and standardised for the analyses. Crude and adjusted coefficients were calculated (linear regression) for all the data collected in follow-up assessments for pacifier use. RESULTS IQ was inversely associated with all pacifier use indicators. Children who used a pacifier all day long (ADL) at any follow-up showed an IQ 0.18 (95% confidence interval [CI] 0.11, 0.24) standard deviations below those who never used it ADL, after adjusting for confounders. The strength of association increased with number of assessments reporting ADL pacifier use, from a reduction in IQ of 0.13 (95% CI 0.06, 0.21) to 0.34 (95% CI 0.15, 0.52) standard deviations for ADL use in one and in all four follow-up visits, respectively. CONCLUSIONS We found a strong association between intense pacifier use up to 4 years of age and lower IQ at 6 years. A dose-response gradient was observed, with greater IQ deficits in children who used a ADL pacifier for longer durations. The mechanisms underlying this association need to be clarified. One hypothesis is that children using a pacifier, especially those who use it more intensely, are less stimulated.