Related Experiment Video
Updated: Aug 10, 2026

A Common Marmoset Model of Mother-Infant Intervention for Breastfeeding Disorders in the Presence of Paternal Inhibition and Maternal Neglect
Published on: September 22, 2023
Breast-feeding and mental and motor development at 51/2 years
Katy M Clark1, Marcela Castillo, Agustin Calatroni
1Center for Human Growth and Development, University of Michigan, Ann Arbor, 48109, USA.
Objective:
Breast-feeding is associated with better child development outcomes, but uncertainty remains primarily due to the close relationship between breast-feeding and socioeconomic status. This study assesses the issue in a low socioeconomic status sample where breast-feeding was close to universal.
Methods:
Seven hundred eighty-four Chilean children were followed longitudinally from infancy. All but four were initially breastfed, 40% nursed beyond 12 months, and infant growth was normal. Child development was assessed at 5(1/2) years by a cognitive, language, and motor test battery. The duration of breast-feeding as the sole milk source was analyzed as a continuous variable, adjusting for a comprehensive set of background factors.
Results:
The relationship between breast-feeding and most 5(1/2)-year developmental outcomes was nonlinear, with poorer outcome for periods of breast-feeding as the sole milk source for <2 months or >8 months--statistically significant for language, motor, and one comprehensive cognitive test, with a suggestive trend for IQ.
Conclusions:
The observed nonlinear relationships showed that breast-feeding as the sole milk source for <2 months or >8 months, compared with 2-8 months, was associated with poorer development in this sample. The latter finding requires replication in other samples where long breast-feeding is common and socioeconomic status is relatively homogeneous.
Related Concept Videos
Piaget's Stage 1 of Cognitive Development
Exploration...
Three Developmental Domains
Physical Development
Physical processes, also known as maturation, encompass the biological changes that occur across an individual's life. These changes begin with genetic inheritance and continue through various stages, including growth in height and weight,...
Introduction to Developmental Psychology
Environmental Influences on Intelligence
Cognitive Development During Adulthood
Development of the Oral Microbiota

