Examining the impact of socio-economic position (SEP) across the life course on cognitive function and brain structure in healthy ageing.

This study explores the relationship of life course inter-generational social mobility with cognitive function and brain structure in older adults using Diagonal Reference Models (DRMs). Data from the Irish Longitudinal Study on Ageing, a population-based cohort of adults aged 50 years and older (N=4,620 participants; mean age: 66.1; SD:9.1; 55% female) was used for analysis. Brain MRI data was available for 464 participants. Social mobility was characterised as the difference between childhood socio-economic position (SEP) (i.e. father's occupation) and adulthood SEP (i.e. own occupation). The Montreal Cognitive Assessment (MoCA), the Mini Mental State Examination (MMSE), cortical thickness and total grey matter volume (GMV) served as global cognitive and brain measures. Exploratory analyses included the volumes of the ventromedial prefrontal cortex (vmPFC), anterior cingulate (AC), hippocampus and amygdala. A social gradient in cognitive function was observed among the inter-generationally stable; brain structure was not as clearly socially patterned. Adulthood SEP was significantly associated with MoCA (weight = 0.76; p<.001), MMSE (weight = 0.91; p<.001), GMV (weight = 0.77; p=.002) and AC volume (weight = 0.76; p<.001), while childhood SEP was associated with vmPFC volume (weight = 1.00; p=.003). There was no independent association of social mobility with any of the outcomes. Together our results suggest that both childhood and adulthood SEP are important in shaping later life brain health, but that adulthood SEP predominates in terms of its influence. This is potentially an important insight as it suggests that brain health may be modifiable if socio-economic circumstances change.