Metabolic health and obesity: Early determinants, trajectories and causal analysis. The Northern Finland Birth Cohort 1966 and 1986 studies.

The obesity epidemic has grown over the last four decades in most European countries including Finland where 21.5% of women and 20% of men are now living with obesity. There is a large body of evidence establishing that the first years of life, including the foetal period, are critical for obesity and general health later in life. However, a better understanding of the link between early life determinants and the life-course trajectory of obesity is needed.
In this thesis, associations between early life determinants and cardio-metabolically healthy obesity, defined as obesity in the absence of any cardiometabolic disorders, were investigated. The relationships between early life determinants and developmental body mass index (BMI) trajectories were explored. Finally, the associations between temperament traits and cardiovascular health and whether eating behaviours and fitness mediated the associations were examined. The research was conducted on data from the prospective Northern Finland Birth Cohorts 1966 (NFBC1966) and 1986 (NFBC1986) using association analyses, latent trajectory modelling and causal mediation analysis.
The first study suggested that early life determinants such as age at adiposity rebound were associated with cardio-metabolically healthy obesity and that the association differed between males and females. In the second study, developmental BMI trajectories were modelled from NFBC1966 and NFBC1986. Adverse maternal factors were associated with unfavourable BMI trajectories. A different pattern of association between age at adiposity peak and BMI trajectories was found between the different cohorts, uncovering secular trends. The third study provided evidence that associations between temperament traits, established early in life, and cardiovascular health measures could be sex-specific. Furthermore, eating behaviours and mediators involved in the associations seemed to be associated with sex.
The research undertaken in this thesis provides evidence to support the effect of early life determinants on life-course metabolic health and highlights the role of sex in these pathways. In addition, this work further advances the importance of psychological factors in relation to metabolic health with a specific focus on sex-specific temperament and behavioural mediators.