Low socioeconomic position (SEP) has been linked to an increased risk of dementia. However, little is known about the association between SEP trajectory and regional brain volumes related to dementia. A random sample of community-dwelling older adults (n = 428, age = 73.1±5.5) living in Tokamachi City (Niigata Prefecture, Japan) without medical histories of dementia, Parkinson's disease, and depression who underwent automated assessment of brain volumes on magnetic resonance imaging and responded to a self-administered questionnaire survey in 2017. We measured SEP in childhood (household SEP at age 15), young adulthood (education), mid-adulthood (the longest occupation), and late adulthood (current wealth), and further performed group-based trajectory analysis to identify lifetime trajectory patterns on SEP. Multivariate regression models were employed to investigate the association between SEP trajectories and 4 regional brain volumes related to the development of Alzheimer's disease (ie, entorhinal cortex, hippocampus, amygdala, and the parahippocampus), the most common type of dementia. We found 3 distinct SEP trajectories (stable middle class [68%], downward [23%], and upward [9%]). Compared to those who experienced stable middle class, older adults who experienced the upward SEP mobility had significantly larger hippocampus (β: 213.2, 95% confidence interval: 14.7, 411.8). On the other hand, older adults who experienced downward SEP mobility showed no significant differences in any of the 4 brain structural volumes. Our findings indicate that upward life-course SEP mobility is associated with larger volumes of hippocampus in old age. SEP trajectory may offer us a useful lens to enhance our understanding of the etiology of dementia.
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