Daily Use of Pacifier in the First Years of Life Is Associated with Lower IQ at Age Six

Abstract

Background: Literature on pacifier use is controversial, but mostly suggests negative effects especially on breastfeeding, dental occlusion, and speech development. Little is known about its influence on intelligence. This study assessed the influence of pacifier use duration and intensity on intelligence quotient (IQ) scores in six-year old children from a birth cohort.   Methods: Data from 3,532 children from the 2004 Pelotas (Brazil) Birth Cohort were analyzed. Children were recruited and assessed at birth and followed-up at three months and at one, two, four, and six years. IQ was estimated using the Wechsler Intelligence Scale for Children. Data on pacifier use duration/intensity were obtained via interviews with mothers at all follow-up visits before age six. Crude and adjusted effects of pacifier use were assessed through linear regression. Findings: IQ was negatively associated with all pacifier use indicators. Children who used a pacifier all day long at any assessment had an IQ 0·18 SD lower than those who never used it all day. This effect increased with the number of assessments where all-day-long pacifier use was reported. Children who reported all-day-long pacifier use in the four assessments had an IQ 0·34 SD lower than those who never used it all day.   Interpretation: We found strong evidence that intense pacifier use up to four years of age is associated with lower IQ at six years. A dose-response effect was observed, with greater IQ reduction in children who used a pacifier for longer. The mechanisms underlying this association need to be clarified.   Funding Statement: Universidade Federal de Pelotas, ABRASCO, Wellcome Trust (2009-2013), WHO, PRONEX, CNPq, the Brazilian Ministry of Health, and the Child Pastorate. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: Written informed consent was obtained from all mothers or guardians before data collection. The research ethics committee of the Universidade Federal de Pelotas Medical School approved all follow-up waves of the 2004 Pelotas (Brazil) Birth Cohort.