Socioeconomic disparities in six-year incident dementia in a nationally representative cohort of U.S. older adults: an examination of financial resources

Dementia affects 47 million individuals globally [1]. Low-resourced populations tend to experience disproportionately higher dementia rates [2, 3] but associations between socioeconomic status and incident dementia are under-examined. Socioeconomic status is a multi-dimensional construct capturing both tangible and intangible resources that can prevent dementia via different intervening mechanisms [4]. As examples, higher educational training and greater occupational complexity are believed to contribute to greater cognitive reserve, which is an intangible resource that may prevent clinical signs of dementia despite pathological changes [5], whereas financial resources, such as income and financial strain, are more important for tangible resources such as nutrition and health care [4]. Determining which dimensions of socioeconomic status contribute to incident dementia could guide prevention and policies directed at lowering risks.

Not all socioeconomic measures have been examined with regard to incident dementia in population-based samples. Low education [3] and low occupational complexity [6] have both been associated with incident dementia in population-based studies. In fact, low education has been identified as a contributor to excess dementia incidence in the U.S. and globally [1, 7]. However, there is less data about whether income and financial strain predict incident dementia independent of education in national samples of older adults, despite two good reasons to investigate. First, income and financial strain have been consistently associated with health-related dementia risk factors, such as cardiovascular disease, smoking and depression [3, 8‐10]. Secondly, there is some evidence linking income and financial strain with dementia independent of education, but results are not consistent across studies. Although income did not predict dementia-related mortality in a large sample of Norwegian men [11], lower income predicted memory decline in the U.S. nationally representative Health and Retirement Study [12], both lower income and financial strain predicted incident dementia in the Health ABC study, which sampled healthy black and white U.S. older adults [2], and fewer financial assets, which is related to income and financial strain, predicted incident dementia in a nationally representative sample of English older adults [13]. Also, it is important to test both income and financial strain, since income improves the quantity and quality of resources to prevent dementia and financial strain reflects whether the income is sufficient for an individual’s cost of living and financial commitments. Therefore, the current study tested the hypothesis that financial resources, including income and financial strain, predict incident dementia over 6 years independent of education and occupation among a nationally representative sample of adults aged 65 years and older.

The six-year cumulative incidence of dementia was approximately 10.5% (Table 1), which extrapolates to 3,100,530 U.S. older adults transitioning to dementia over 6 years. Annual incidence rates ranged from 2.0% (95% CI: 1.5 to 2.5%) to 3.8% (95% CI: 3.2 to 4.4%) in the weighted sample (Fig. 1). Participants free of dementia in 2012 who were included in the analytic sample were typically < 75 years old (58%), female (56%), retired (51%), homeowners (55%) and white (84, 8% were black, 6% Hispanic, and 3% were other racial or ethnic groups). Characteristics according to dementia status by study completion (2018) are summarized in Table 1. Older adults who developed dementia (n = 679) were more likely to report financial strain at baseline, to have less than high school education, and were less likely to have worked mainly in a professional occupation than those who remained free of dementia in 2018 (n = 4355). The mean income to poverty ratio did not differ by 2018 dementia status in the total sample, but among a subset of participants with incomes < 500% poverty, those with incident dementia had a lower average income to poverty ratio than their peers who remained free of dementia in 2018. Those with incident dementia were older and more likely to be female, black or Hispanic than white, more likely to report diabetes, a history of stroke and experience depressive symptoms.

Bivariate standardized coefficients between the socioeconomic measures revealed key differences across measures. Financial strain was strongly inversely associated with income (B = − 0.974, p < 0.001), but had modest associations with education (B = − 0.273, p < 0.001) and professional occupation (B = − 0.165, p < 0.001). Education was moderately positively associated with both income (B = 0.713, p = 0.004) and professional occupation (B = 0.594, p < 0.001). Income was not associated with professional occupation (B = 0.202, p = 0.490).

Adjusting for age, race/ethnicity, gender, home ownership, retirement, and all socioeconomic measures, three socioeconomic measures predicted incident dementia over 6 years (Table 2, Model 1). Financial strain predicted higher odds, while higher education and higher income (among those with incomes < 500% poverty threshold) predicted lower odds of incident dementia. Effect sizes were similar across these three measures; hazard odds ratio estimated between 19 and 28% higher or lower odds of incident dementia. Professional occupation and higher income among those with incomes exceeding the 500% threshold did not predict incident dementia. Additional adjustment for health-related dementia risk factors did not alter inferences (Table 2, Model 2) and hazard odds ratios were similar to those in Model 1. As shown in Fig. 2, hazard odds ratios were fairly similar for financial strain, education, and higher income among participants with incomes < 500% poverty. Four separate sensitivity analyses were conducted as described in statistical methods and inferences were unchanged for each (results not shown).

This is the first nationally representative study of older adults showing that lower income and financial strain predict incident dementia and have associations distinct from low education but comparable in size. This study builds on prior studies linking income and financial strain with cognitive changes in older adults [2, 12]. Together, these results suggest that dimensions of socioeconomic status beyond education place individuals at risk with regard to dementia. These results call for greater attention to the role of financial resources and the lack thereof as predictors of dementia risk in older adults.

Why do lack of financial resources place older adults at increased risk for dementia? In this study, three components of socioeconomic status - financial strain, income and education - were independently associated with incident dementia. These results are consistent with the conceptual understanding of socioeconomic status as a multi-dimensional concept, each contributing to incident dementia via different intervening mechanisms [4]. Less cognitive reserve likely represents a key mechanism linking low education with incident dementia [5], but may not explain effects of income and financial strain noted in this study. Income and financial strain were not strongly correlated with education in this study, suggesting that they capture a different dimension of socioeconomic status. Both income and financial strain capture financial resources that can promote health. Despite the strong correlation between them, both measures independently predicted incident dementia, suggesting that both financial resources are important predictors of incident dementia. These results add incrementally to the other modifiable risks identified in The Lancet Commission on Dementia Report, which, if addressed, could further reduce population dementia risk beyond the one-third reduction proposed in that report [1].

These results add to prior literature linking financial resources with aging-related outcomes; low income and financial strain have predicted earlier mortality [22, 23] and disability [24]. Notably, in this and a prior study [22], income was most strongly associated with health outcomes among those living at or near the poverty threshold. Together, these results warrant further attention to explore intervening mechanisms between financial resources and aging-related outcomes for older adults and suggest that the lowest income individuals should be targeted for prevention efforts.

Notably, three socioeconomic measures remained significant in regression models that adjusted for health-related dementia risk factors, suggesting that socioeconomic associations with dementia risk cannot be attributed to late life chronic disease, smoking history and depression. Although it is possible that the physiologic mechanisms linking chronic disease to dementia risk occur prior to older ages [25, 26], it is also possible that current socioeconomic status confers additional dementia risk via pathways unrelated to chronic disease burden. The theory of fundamental causes proposes that low socioeconomic status causes disease through multiple mechanisms [4]. One key mechanism may include physiologic dysregulation due to relatively more exposure to negative life events and adverse environmental conditions that provoke stress response mechanisms in low socioeconomic status groups. Physiologic dysregulation predicts earlier disability, mortality and cognitive decline [27]. A second mechanism may include less attention to cognitive tasks because of relatively more attention consumed by financial worries [28]. Regardless of the mechanisms, these results suggest that interventions that solely target older adult health-related risk factors will likely not prevent dementia for low socioeconomic status groups. One study showed that recent U.S. declines in dementia prevalence are likely due to age- and education-shifts in the population [17], suggesting that efforts to address socioeconomic exposures may reduce the global dementia burden. Together, these studies suggest that interventions aimed at preventing dementia should move upstream in the causal chain by addressing socioeconomic conditions.

Financial resources may be more modifiable than other socioeconomic dimensions among older adults. Despite the empirical link between education and dementia, education typically captures early life opportunities, whereas financial resources capture an older adult’s current resources. Similarly, while education is not typically acquired in midlife or late life when individuals experience the greatest risk for dementia, financial strain may be modified in late life by improving access to programs providing financial assistance for daily necessities. Financial strain suggests two possible intervention targets –increasing income or decreasing expenses such as medication costs. As examples, one study found that a randomly distributed influx of income improved attention and fluid intelligence scores for low-income adults [28], suggesting that increased financial resources may improve cognitive ability. Also, financial strain is less strongly associated with lower well-being in European countries with relatively more generous welfare programs [29]. As U.S. examples, the implementation of Medicare Part D is associated with lower cost-related medication non-adherence [30] and participation in the Supplemental Nutrition Assistance Program (SNAP) improves an individual’s ability to afford food [31], reduces health care utilization [32, 33], and reduced cost-related medication non-adherence [34]. Despite documented benefit from SNAP, only 42% of eligible older adults actually participate in SNAP [35] and the complex enrollment process for such programs may pose a barrier for older adults. Rigorous evaluation of public benefits and other programs may improve our understanding of how to reduce financial strain for vulnerable older adults.

Dementia is burdensome, costly and feared. Given the financial burdens of dementia on individuals and families [36], attending to financial strain as a risk factor is important. These results contribute to prior studies by showing in a national representative sample that individuals with the fewest financial resources are the most likely to acquire dementia. Prior work has identified multiple modifiable risk factors for dementia [1] and this study builds on those findings by identifying financial resources as a potentially modifiable risk factor. Greater attention is needed to improve financial support for dementia-related prevention and care for low-income and financially strained older adults.