Growth in early life and childhood IQ at age 11 years: the Newcastle Thousand Families Study

Background It has been suggested that in addition to genetic factors, fetal and post-natal growth influence childhood cognition, although it is unclear whether such an effect continues throughout childhood. This study aimed at investigating the potential relationships between childhood IQ at age 11 years and birth weight and height at the ages of 9 and 13 years, after adjusting for the confounding factors available to this investigation. Methods The Newcastle Thousand Families study, a prospectively followed cohort, originally consisted of all 1142 births in the city of Newcastle in May and June 1947. Using data on 733 members of this cohort, we investigated the associations between IQ at age 11, and birth weight and height at ages 9 and 13 years. Results Birth weight showed no association with childhood IQ. However, height at age 9 years was a significant predictor of childhood IQ after adjusting for socioeconomic status (standardized regression coefficient b = 2.6, 95% Cl 1.6-3.6, P < 0.0001). Height at age 13 was also a significant predictor of IQ after adjusting for socioeconomic status (b = 3.4, 95% CI 2.3-4.4, P = 0.001), and explained an additional 2.5% of the variation in IQ scores to that already explained by socioeconomic status and height at age nine. Conclusions These results suggest a continuing effect of post-natal growth on childhood cognition beyond the age of 9 years. Post-natal growth, which may be influenced by genetic factors and nutrition and socioeconomic circumstances in childhood, may be more important than fetal growth in terms of childhood cognition.