Pubertal timing and mental health. Understanding social and genetic determinants

Abstract

Background: Previous research has found associations between poor mental health and early puberty (EP). Genetically informed studies provide conflicting evidence on whether the association between mental health and EP is transient / confounded by variables like Body Mass Index (BMI).

Methods: The thesis is based on two large studies: a) The International Health Behaviour in School-Aged Children Study, providing cross-sectional evidence on pubertal timing and life circumstances in 36 countries and regions; b) The Avon Longitudinal Study on Parents and Children with longitudinal and genetic data on puberty and psychiatric impairment. The thesis relies on longitudinal and auto- regressive modelling, genetic correlations, Mendelian Randomization, as well as cross-cultural associations to elucidate the research question.

Results: 1) The study verifies the so-called “Stepfather-effect” which is measurable on a cross-cultural level (girls in families with stepfathers experience earlier puberty). However, some of these differences can be explained by differences in BMI and lifestyle between different families. 2) It is shown that there is no evidence for prepubertal psychiatric impairment caused by early puberty. Mendelian Randomization suggests a peripubertal, but no prepubertal effect in girls. 3) Genetic correlations reveal no genetic overlap of EP with mental health, but with BMI and socioeconomic traits; 4) Cross-culturally, EP is related to higher life expectancy and an overall lower burden of disease for psychiatric disorders. Overall, EP in girls is more prevalent in the lower socioeconomic strata mainly in English-speaking and Northern European countries.

Discussion: The study contradicts an “accentuation hypothesis” that prepubertal differences in psychopathology accentuate after puberty, because in girls they are not present pre-pubertally and in boys they diminish over time. The thesis makes a case for understanding pubertal timing as a socioeconomic variable because of its strong association with BMI. To be informative, studies need to disentangle the biological from the socioeconomic signal.