Social environment, lifestyle, and genetic predisposition with dementia risk: A long-term longitudinal study among older adults

Background The role of social environment, i.e., the aggregate effect of social determinants of health (SDOHs), in determining dementia is unclear. Methods We developed a novel polysocial risk score for dementia based on 19 SDOH among 5,199 participants in the Health and Retirement Study, US, to measure the social environmental risk. We used a survival analysis approach to assess the association between social environment and dementia risk in 2006-2020. We further studied the interaction between social environment and lifestyles, and explored racial disparities. Results The study participants (mean age=73.4 years, SD=8.3; 58.0% female; 11.6% African American) were followed up for an average of 6.2 years, and 1,089 participants developed dementia. Every one-point increase in the polysocial risk score (ranging from 0-10) was associated with a 21.6% higher risk (aHR=1.21, 95% CI=1.15-1.26) of developing dementia, other things being equal. Among participants with high social environmental risk, regular exercise and moderate drinking were associated with a 43-60% lower risk of developing dementia (p<0.001). In addition, African Americans were 1.3 times (aHR=2.28, 95% CI=1.96-2.66) more likely to develop dementia than European Americans, other things being equal. Discussion An adverse social environment is linked to higher dementia risk, but healthy lifestyles can partially offset the increased social environmental risk. The polysocial risk score can complement the existing risk tools to identify high-risk older populations, and guide the design of targeted social environmental interventions, particularly focusing on improving the companionship of the older people, to prevent dementia.