Social determinants of health, behavioral factors, and incident dementia: a prospective cohort study

While individual associations between social determinants of health (SDoH), behavioral factors, and incident dementia have been established, the cumulative effect of multiple unfavorable SDoH and their interaction with behavioral factors remains poorly understood. We aimed to examine the independent and joint associations of SDoH and behavioral factors with incident dementia risk in middle-aged and older adults. This prospective cohort study utilized data from the Health and Retirement Study. Participants who were dementia-free at baseline, with complete information on SDoH and behavioral factors, and with at least one cognitive assessment during the study period (2006–2020) were included. SDoH, and behavioral factors were sourced from self-reported information. Dementia was assessed biennially using a validated algorithm. Among 17,303 initially dementia-free participants (mean baseline age 63.75 [10.43] years, 58.30% women), 1,942 incident dementia cases were documented over a median follow-up of 9.61 years (IQR, 6.33–13.83). After multivariable adjustment, several unfavorable SDoH and behavioral factors were independently associated with higher dementia risk (P-value < 0.05). Among them, less than high school education emerged as the strongest predictor (hazard ratios [HR] 2.64, 95% confidence interval [CI]: 2.37–2.94), followed by lower household income (HR 1.51, 95% CI: 1.33–1.72). A dose–response association of cumulative unfavorable SDoH (HR per additional disadvantage: 1.42, 95% CI: 1.39–1.45) and behavioral factors (HR per additional factor: 1.31, 95% CI: 1.38–1.44) with dementia risk was also observed. Participants with ≥ 5 unfavorable SDoH and ≥ 2 unfavorable behavioral factors had the highest dementia risk (HR 9.22, 95% CI: 7.28–11.66) compared to those with minimal exposures. This prospective cohort study reveals that cumulative exposure to unfavorable SDoH and behavioral factors is significantly associated with increased dementia incidence, with potential synergistic effects that could amplify risk. Addressing these unfavorable SDoH and maintaining optimal behavioral health is crucial for delaying or preventing dementia.