A wealth of research has reinforced the idea that supportive and connected social relationships have a positive effect on mental health. The association between social relationships and mental health is affected by top-down socioeconomic conditions and bottom-up biological factors, including the structure of the brain. These factors are not fixed; there is a dynamic, reciprocal interplay which affects a personâs mental health. This thesis aimed to 1) investigate those multiple levels in tandem to predict mental health, 2) understand the role of different points in the life course â adolescence and older age â and 3) determine the role of sex differences in the role of those multiple factors to predict mental health. Study One tested a cross-sectional model investigating the role of functional aspects between peer and family relations, socioeconomic stress, and amygdala and ventromedial prefrontal cortex grey matter volume in predicting emotional symptoms in early adolescence. Study Two investigated the direction of the associations between peer and family relationships, emotional symptoms, and amygdala and ventromedial prefrontal cortex grey matter volume between ages 14 and 19 years. Study Three conducted both a cross-sectional and longitudinal analysis of data from older adults aged 60 years and above to investigate structural and functional aspects of social relationships in relation to psychological distress, socioeconomic status, and amygdala and ventromedial prefrontal cortex grey matter volume. Findings indicated that the functional aspects of social relationships changed together with emotional functioning in both early and late life, and the importance of adolescence as a sensitive period for structural brain plasticity according to the social environment was highlighted. To add, socioeconomic status and sex were implicated in social relationships, mental health, and regional brain structure, which contributed to differing effects in adolescence and older age. Altogether, the findings show the nuance between the role of social relationships, socioeconomic status, and brain structure in terms of specific facets studied, time point investigated, and individual characteristics. This thesis has implications for specificity in intervention approaches and methodological approaches for future research. For example, latent change score modelling, latent variable modelling, and measurement invariance testing should be more widely adopted to strengthen the ability to detect robust, directional effects, and to clarify the specific factors contributing to mental health across the lifespan.
- older age
- structural equation modelling
- brain structure
- social relationships
- mental health