Methods: We repeatedly examined 25889 siblings within the Norwegian Mother and Child Cohort Study, following them from the mothers' pregnancy through child age 8 years. Information on the children's height and weight was collected by means of health registries and maternal reports. Information on the siblings' temperament was collected by questionnaires completed when they were 1.5, 3, and 5 years old. We examined the associations of temperament at different child ages with the timing of the adiposity rebound among siblings and controls by means of growth curve and multilevel analyses.
Results: Within siblings, high scores on the approach trait of sociability predicted an earlier adiposity rebound and high scores on the avoidance trait of shyness predicted a later adiposity rebound with timing differences ranging between 6 and 16 weeks. Surprisingly, negative emotionality did not predict the adiposity rebound. The associations between temperament and the adiposity rebound increased with increasing child age. The results within controls-comparing siblings with the population, broadly paralleled those within siblings.
Conclusions: The findings encourage the notion that child temperament functions as an early marker for the adiposity rebound. Future studies may advance our knowledge by including measures of child personality along the taxonomy of the adult Five Personality Factors.