The Associations of Sensory Impairment With 10-Year Risk of Dementia and Alzheimer’s Disease: The Health and Retirement Study,2010-2020

Abstract

Background

Studies have examined the association between dual sensory impairment and late-life cognitive outcomes in the U.S with inconsistent findings.

Objective

To examine the associations between sensory impairment and 10-year risk of dementia or Alzheimer’s disease among U.S. adults aged ≥ 50.

Methods

A prospective cohort study based on the Health and Retirement Study from 2010 to 2020. Individuals aged ≥ 50 years without self-reported dementia and Alzheimer’s disease in 2010 were included in the analysis. Self-reported visual and hearing impairments were measures in 2010. Main failure events included self-reported incident dementia and Alzheimer’s disease over a 10-year follow-up period. Participants were categorized as having no visual or hearing impairment, visual impairment only, hearing impairment only, and dual sensory impairment. Fine-Gray competing risk regression model was applied to estimate the associations of sensory impairment with incident dementia and Alzheimer’s disease, adjusted for demographic characteristics, health behaviors, and health conditions at baseline.

Results

Of 20,248 identified individuals, 14.6% had visual impairment only, 11.2% had hearing impairment only, and 9.1% had dual impairment at baseline. After adjusting for all covariates, dual sensory impairment was associated with higher risk of dementia (HR = 1.46, 95% CI: 1.23-1.73) and Alzheimer’s disease (HR = 1.35, 95% CI: 1.03-1.76). Visual impairment only was also associated with incident dementia and Alzheimer’s disease among individuals <65 years.

Conclusion

Older adults in the U.S. with visual and hearing impairments simultaneously had a particularly greater risk of dementia and Alzheimer’s disease, indicating the needs of targeted screening for timely treatment and further prevention of dementia and Alzheimer’s disease.

Keywords

sensory impairment dementia Alzheimer’s disease aging

Introduction

Alzheimer’s disease and Related Dementias have become urgent public health concerns. About 1 in every 10 Americans aged 65 years and older were living with dementia in 2016, with a disproportionate burden among Black and Hispanic adults and individuals with low education attainment and limited health literacy.^1,2 The increasing prevalence of dementia poses significant health and economic burden on both individual patients and society, with an estimated worldwide cost of $2 trillion U.S. dollars in 2030.³ Hence, with rapid population aging worldwide, identifying preventive measures regarding risk factors for dementia in older people has great public health importance.

Sensory impairments, specifically vision and hearing impairment, are individually associated with a higher risk of incident dementia,^4–7 and share multiple risk factors with dementia (e.g., central nervous structure degeneration, cardiovascular diseases, social isolation, depression).^8–11 The combined hearing and vision impairment, also known as dual sensory impairment, has been increasingly prevalent among midlife and older adults.^12–14 Dual sensory impairment is a specific type of disability with which an individual experiences any level of concurrent vision and hearing impairment, independent of severity or order of onset.^15–17 It tends to have more severe consequences on individuals than the sum of each single sensory impairment.¹⁸ However, evidence has been relatively limited on how dual sensory impairment was related to incident dementia.

Several studies have shown dual sensory impairment is associated with excess risk of incident dementia,^19–23 while others found no associations.^24,25 One recent study showed that compared with individuals without sensory impairments, dual sensory impairment is associated with higher risk of all-cause dementia and Alzheimer disease in the Cardiovascular Health Study (CHS).²⁶ Another study which used the National Health and Aging Trends Study (NHATS) and focused on community-dwelling, Medicare beneficiaries also found a positive association between dual sensory impairment and incident dementia.²⁷ While these studies provided important evidence of dual sensory impairment with incident dementia, they only focused on late-life adults (aged 65 and older), while hearing loss in midlife has been considered a risk factor for dementia.⁴ Additionally, one study examined the association between sensory impairment and probable dementia in the Health and Retirement Study (HRS) among participants ≥50 years old, and no association was found after adjustment for all covariates.²⁸ It is noticeable that in this study, the measurement of dementia in the HRS is based on a few cognitive tests, without physician diagnosis which is often obtained with an assessment of potentially treatable conditions related to cognitive difficulties, review of patients’ medical and family history, and procedures including but not limited to brain scan, psychiatric evaluation, genetic tests, and blood tests.²⁹ Therefore, further evidence is needed regarding the associations of sensory impairments with incident dementia in mid-to-late-life adults.

Using the HRS cohort with more recent data and self-reported diagnosis of incident dementia, we aimed to extend existing research to examine how visual and hearing impairment are separately and jointly associated with the incidence of dementia, including Alzheimer’s disease, the major type of dementia, while taking death into account as a competing risk. Based on existing literature, we hypothesized that having visual and hearing impairments are jointly associated with the incident dementia (including Alzheimer’s disease) and the association is greater than the sum of associations for having single sensory impairment.

Methods

Study Population and Sample

The study population was based on the HRS, a nationally representative survey of adults aged ≥50 years in the United States. The study used a longitudinal cohort sample with a steady-state design that replenishes the sample every six years with younger cohorts. Participants were interviewed face-to-face or by telephone for information collection, including income, work, assets, health insurance, physical health and functioning. The HRS offered assistance and opportunities to use a proxy respondent to participants who were unable or unwilling to complete an interview themselves, including but not limited to individuals with certain physical symptoms (e.g., hearing problems, speech problems, severe and permanent illness) and potential symptoms of cognitive impairment. With the use of proxy respondent, the attrition bias was shown to be reduced in measured cognition.³⁰ Our analytical cohort started with 20,340 individuals aged ≥50 years without dementia or Alzheimer’s disease who rated their hearing and vision at time of Wave 10 (2010), the baseline of our study, as this was the first wave with information of self-reported dementia and Alzheimer’s disease available. We additionally excluded 92 participants who had missing information in education, which is highly related to cognitive outcomes. We used the multiple imputation by chained equation (MICE) algorithm to impute any missing observation among the other baseline covariates (see Table 1).³¹ MICE was implemented using the “mice” package in R with 5 sets of imputation.

Table 1.

List of Variables Imputed Using the MICE Algorithm.

Variable name	Data type
Race	Categorical
Smoking	Categorical
Drinks per day	Numeric
Physically active	Categorical

Measures

Vision and hearing abilities were self-evaluated at baseline (2010). Participants were asked “Is your hearing excellent, very good, good, fair, or poor” (among participants who reported not wearing a hearing aid), or “Is your hearing excellent, very good, good, fair, or poor using a hearing aid as usual” (among participants who reported wearing a hearing aid). Participants who reported “fair” or “poor” were considered having hearing impairment. Similarly, participants were asked “Is your eyesight excellent, very good, good, fair, or poor using glasses or corrective lenses as needed”, and participants who reported “fair” or “poor” were considered having visual impairment.

Two main failure events – self-report diagnosis of incident dementia and Alzheimer’s disease were obtained at each wave. Participants were asked the questions “Has a doctor ever told you that you have dementia, senility or any other serious memory impairment” and “Has a doctor ever told you that you have Alzheimer’s Disease”. These measures have been used in literature and exhibited a moderate level of agreement with studies that used in-home cognitive assessment to determine dementia diagnosis.^32–35 Participants can dispute their previously reported self-reported diagnoses when they are re-interviewed in the HRS. Death and year of death were recorded from report by household members and through matching with the National Death Index.

The endpoint of the study of this closed cohort was the reporting of incident dementia (including Alzheimer’s disease), death, or the end of follow-up (Wave 15, 2020), whichever occurred first. Particularly, if a respondent ever reported dementia, we looked at which wave they first reported and defined survival time based on that using the interview date midpoint for that wave. For respondents who were alive and reported no dementia ever in 2020, they were censored at the interview midpoint date of Wave 15. For respondents who were dropouts (N = 201), or had no information in a Wave, we treated them as censored and used the last Wave with available information to define their censored time (observed time).

Covariates

To account for potential confounders associated with sensory impairment, dementia, and Alzheimer’s disease, we included covariates in the analysis, all measured at the baseline of our study (2010). We controlled for individual characteristics, including age, sex (men, women), race (White, Black, other), number of years of education, marital status (currently married or not). We also included baseline health behavior and health conditions, including smoking status (current, former, never), alcohol drinking (number of drinks per day among participants who reported drinking), physical activity (>1 time a week for moderate-to-vigorous physical activity), hypertension, diabetes, heart disease, stroke. All these covariates were collected via a self-reported questionnaire.

Statistical Analysis

Baseline characteristics of participants were descriptively analyzed and presented for the full sample and stratified by sensory impairment status (no visual or hearing impairment, visual impairment only, hearing impairment only, and dual impairment). Differences among the groups were examined using analysis of variance (ANOVA) or Chi-squared tests. Fine-Gray competing risk regression models were used to model the sub-distribution hazard functions of dementia (and Alzheimer’s disease separately) over 10 years of follow-up periods, with adjustment for the covariates mentioned above.³⁶ Death from any causes was considered as competing risk in the analysis. For sensitivity analysis, we combined dementia or Alzheimer’s disease with death as a composite outcome and used a Cox proportional hazard model for analysis, as an alternative strategy for dealing with competing risks.^37–39 Sub-distribution hazard ratios (HRs) for dementia or Alzheimer’s disease and 95% confidence intervals (CIs) were reported. All analyses have been performed in R version 4.0.4.

Results

A total of 20,248 individuals were included in the analyses. The mean age was 66.7 ± 11.0 years, and 42.9% were male. White and Black participants accounted for 72.8% and 19.2%, respectively, and 62.8% were married or partnered. The average years of education received was 12.6 ± 3.2; 56.8% were current or former smokers, and the daily average alcohol drinks was 0.8 ± 1.6; 57.2% ever had hypertension, and 21.7%, 21.9%, and 7.7% had diabetes, heart disease, ever had a stroke, respectively. Half (52.4%) of the participants were physically active (Table 2). Among all participants, 2965 (14.6%) and 2063 (11.2%) reported visual impairment only and hearing impairment only, respectively. Another 1841 (9.1%) participants reported dual impairment. Compared to those without self-reported sensory impairment, participants with sensory impairment had fewer years of education, more were likely to be smokers and have hypertension, diabetes, heart disease, and stroke, and were less physically active, with participants having dual sensory impairment showing the greatest difference (Table 2). For the dementia analysis, 1327 (6.6%) individuals reported a dementia diagnosis first during 10 years of follow-up, and 4807 (23.7%) deaths occurred. For the analysis of Alzheimer’s disease, 515 (2.5%) individuals reported an Alzheimer diagnosis first and 5231 (25.8%) death occurred. The median follow-up duration was 9.1 years (Interquartile range = 4.5 years; Range = 0 – 11.0 years).

Table 2.

Baseline Characteristics of Participants.

	Total (n = 20,248)	No visual or hearing impairment (n = 13,178)	Visual impairment only (n = 2965)	Hearing impairment only (n = 2264)	Dual impairment (n = 1841)
Age, year	66.7 ± 11.0	65.8 ± 10.4	65.6 ± 11.2	71.1 ± 11.4	70.0 ± 12.5
Men, n (%)	8682 (42.9%)	5362 (40.7%)	1088 (36.7%)	1342 (59.3%)	890 (48.3%)
Race, n (%)
White	14,705 (72.8%)	9849 (74.9%)	1712 (57.9%)	1914 (84.7%)	1230 (67.3%)
Black	3886 (19.2%)	2376 (18.1%)	877 (29.7%)	223 (9.9%)	410 (22.4%)
Other	1607 (8.0%)	931 (7.1%)	365 (12.4%)	124 (5.5%)	187 (10.2%)
Education, years	12.6 ± 3.2	13.2 ± 2.9	11.5 ± 3.4	12.5 ± 3.1	10.5 ± 3.9
Married or living with partner, n (%)	12,720 (62.8%)	8611 (65.3%)	1590 (53.6%)	1502 (66.3%)	1017 (55.2%)
Smoking, n (%)
Current	3075 (15.3%)	1778 (13.6%)	695 (23.6%)	279 (12.4%)	323 (17.7%)
Former	8353 (41.5%)	5336 (40.7%)	1107 (37.5%)	1118 (49.7%)	792 (43.3%)
Never	8697 (43.2%)	5984 (45.7%)	1147 (38.9%)	853 (37.9%)	607 (39.0%)
Drinks per day	0.8 ± 1.6	0.8 ± 1.5	0.9 ± 1.9	0.8 ± 1.6	0.8 ± 2.0
Physically active, n (%)	10,585 (52.4%)	7517 (57.1%)	1281 (43.3%)	1146 (50.8%)	641 (34.9%)
Hypertension, n (%)	11,576 (57.2%)	7062 (53.6%)	1875 (63.2%)	1406 (62.1%)	1233 (67.0%)
Diabetes, n (%)	4387 (21.7%)	2437 (18.5%)	856 (28.9%)	514 (22.7%)	580 (31.5%)
Heart disease, n (%)	4444 (21.9%)	2399 (18.2%)	734 (24.7%)	669 (30.0%)	632 (34.3%)
Stroke, n (%)	1552 (7.7%)	739 (5.6%)	339 (11.4%)	225 (9.9%)	249 (13.5%)

Compared to those without sensory impairment, the incidence of dementia was higher among individuals having visual impairment only, hearing impairment only, and dual sensory impairment over time, with individuals with dual sensory impairment showing the highest incidence of dementia and Alzheimer’s disease (Figure 1). Over the total of 10 years of follow-up period, cumulative incidence of self-reported dementia was 6.1% (95% CI: 5.6%-6.6%) in individuals without sensory impairment, 7.9% (95% CI: 6.9%-9.1%) in individuals with visual impairment only, 9.3% (95% CI: 8.0%-10.7%) in individuals with hearing impairment only, and 13.6% (95% CI: 11.9%-15.4%) in individuals with dual sensory impairment. Cumulative incidence of self-reported Alzheimer’s disease was 2.4% (95% CI: 2.1%-2.7%) in individuals without sensory impairment, 2.9% (95% CI: 2.2%-3.6%) in individuals with visual impairment only, 3.2% (95% CI: 2.5%-4.1%) in individuals with hearing impairment only, and 5.5% (95% CI: 4.4%-6.8%) in individuals with dual sensory impairment.

After adjustment for all covariates, dual sensory impairment was significantly associated with higher risk of incident dementia (HR = 1.46, 95% CI: 1.23-1.73) over 10 years of follow-up, compared to those without any sensory impairments. Having visual or hearing impairment only was not associated with incident dementia (Table 3). Stratified by age group, participants aged <65 years at baseline had lower rates incident dementia and Alzheimer’s disease relative to participants aged ≥65 years, regardless sensory impairment status (Figure 2). Adjusting for covariates, visual impairment only and dual sensory impairment were both associated with higher risk of incident dementia among participants <65 years (visual impairment only: HR = 1.98 95% CI: 1.38, 2.83; dual sensory impairment: HR = 3.17, 95% CI: 2.12, 4.76), and dual sensory impairment was associated with higher the risk of incident dementia among participants ≥65 years (Table 3). Stratified by sex, the association between dual sensory impairment and incident dementia was larger among females (HR = 1.54, 95% CI: 1.24, 1.91) than males (HR = 1.35, 95% CI: 1.03, 1.75). Vision impairment only was associated with incident dementia only among males (HR = 1.33, 95% CI: 1.01, 1.74) (Table 3).

Table 3.

The Associations of Sensory Impairment With Incident Dementia During 10 years of Follow-Up.

	Dementia					Alzheimer’s disease
	Overall^a	<65 years^a	≥65 years^a	Female^b	Male^b	Overall^a	<65 years^a	≥65 years^a	Female^b	Male^b
	HR (95% CI)	HR (95% CI)	HR (95% CI)	HR (95% CI)	HR (95% CI)	HR (95% CI)	HR (95% CI)	HR (95% CI)	HR (95% CI)	HR (95% CI)
No visual or hearing impairment	Reference	Reference	Reference	Reference	Reference	Reference	Reference	Reference	Reference	Reference
Visual impairment only	1.17 (1.00, 1.37)	1.98 (1.38, 2.83)	1.04 (0.87, 1.25)	1.08 (0.89, 1.32)	1.33 (1.01, 1.74)	1.07 (0.83, 1.38)	2.99 (1.60, 5.62)	0.92 (0.69, 1.23)	1.03 (0.75, 1.40)	1.13 (0.73, 1.77)
Hearing impairment only	1.08 (0.92, 1.28)	1.59 (0.95, 2.66)	1.03 (0.87, 1.23)	1.12 (0.89, 1.42)	1.04 (0.82, 1.32)	0.96 (0.73, 1.27)	1.66 (0.62, 4.47)	0.93 (0.70, 1.24)	0.90 (0.60, 1.34)	1.03 (0.70, 1.52)
Dual impairment	1.46 (1.23, 1.73)	3.17 (2.12, 4.76)	1.33 (1.11, 1.59)	1.54 (1.24, 1.91)	1.35 (1.03, 1.75)	1.35 (1.03, 1.76)	5.27 (2.57, 10.80)	1.21 (0.91, 1.60)	1.30 (0.92, 1.84)	1.39 (0.92, 2.11)

^aModels were adjusted for sex (men, women), race (White, Black, other), number of years of education, marital status (currently married/living with partner or not), smoking status (current, former, never), alcohol drinking (number of drinks per day among participants who reported drinking), physical activity (>1 time a week for moderate-to-vigorous physical activity), prevalent hypertension, diabetes, heart disease, and stroke.

^bModels were adjusted for race (White, Black, other), number of years of education, marital status (currently married/living with partner or not), smoking status (current, former, never), alcohol drinking (number of drinks per day among participants who reported drinking), physical activity (>1 time a week for moderate-to-vigorous physical activity), prevalent hypertension, diabetes, heart disease, and stroke.

Abbreviations: HR = sub-distribution hazard ratio; CI = confidence interval. Bold values indicate significant at the 0.05 level.

Adjusted for all covariates, dual sensory impairment was associated with the incidence of Alzheimer’s disease (HR = 1.35, 95% CI: 1.03, 1.76) compared to those without sensory impairment. Stratified by age groups, having visual impairment only and dual sensory impairment were associated with higher risk of incident Alzheimer’s disease among participants <65 years (visual impairment only: HR = 2.99, 95% CI: 1.60, 5.62; dual sensory impairment: HR = 5.27, 95% CI: 2.57, 10.80). No association between any sensory impairment and incident Alzheimer’s disease was observed among participants >65 years.

For sensitivity analysis that used the combined dementia or Alzheimer’s disease with death outcome and a Cox proportional hazard model, we found that visual impairment only, hearing impairment, and dual sensory impairment were associated with higher risk of composite outcome of dementia and death (visual impairment only: HR = 1.25, 95% CI: 1.17, 1.35; hearing impairment only: HR = 1.08, 95% CI: 1.00, 1.16; dual sensory impairment: HR = 1.29, 95% CI: 1.19, 1.39), as well as the composite outcome of Alzheimer’s disease and death (visual impairment only: HR = 1.23, 95% CI: 1.14, 1.32; dual sensory impairment: HR = 1.23, 95% CI: 1.13, 1.33) (Table 4).

Table 4.

The Associations of Sensory Impairment With Composite Outcome of dementia/Alzheimer’s Disease and Death During 10 years of Follow-Up.^a

	Dementia + death	Alzheimer’s disease + death
	HR (95% CI)	HR (95% CI)
No visual or hearing impairment	Reference	Reference
Visual impairment only	1.25 (1.17, 1.35)	1.23 (1.14, 1.32)
Hearing impairment only	1.08 (1.00, 1.16)	1.04 (0.96, 1.12)
Dual impairment	1.29 (1.19, 1.39)	1.23 (1.13, 1.33)

Abbreviations: HR = sub-distribution hazard ratio; CI = confidence interval.

Discussion

Based on a nationally representative sample of individuals aged >50 years in the United States with logitudinal data, our results showed that having both visual and hearing impairment were independently and jointly associated with a higher risk of dementia and Alzheimer’s disease during a follow-up period of 10 years, with adjustment for potential confounders. Our study extends the literature by including a nationally representative U.S. population with more recent data and focusing on the associations of sensory impairment with risk of self-reported diagnosed dementia and Alzheimer’s disease. Additionally, using the competing risk models allowed us to identify more accurate associations by accounting for the cumulative risk of mortality, a major concern of survival analyses for older adults.

Our findings were consistent with most of the recent findings that dual sensory impairment was associated with a higher risk of dementia, regardless of the use of self-reported measures or clinical test results. Kuo et al showed that self-reported visual and dual sensory impairment were associated with higher risk of incident dementia among community-dwelling, Medicare beneficiaries aged 65 years and older in the U.S.²⁷ Our study extends this research by focusing on a larger population of individuals aged 50 and older regardless of health insurance status. Hu et al. showed that objective measures of visual, hearing, and dual sensory impairment were associated with an increased risk of developing dementia using the data from the UK Biobank, and the magnitude of the association between dual sensory impairment and incident dementia was the greatest.⁴⁰ Hwang et al. found that older adults with self-reported dual sensory impairment have a significantly higher risk for dementia in the Gingko Evaluation of Memory Study.⁴¹ Hwang et al. also showed that self-reported dual sensory impairment is associated with a higher risk of dementia among older adults in the CHS.²⁶ Maruta et al. showed that older adults with any objective measure of sensory impairments have a high incidence of dementia, and those with dual sensory impairment have the greatest risk in the Japanese population.²¹ Although a recent prospective cohort study of participants in Germany found no excess risk of all-cause dementia among those reporting dual sensory impairment, it is probably due to low statistical power of the German study that only 229 (6.5%) of the participants who had dual impairments reported dual impairments at baseline.²⁵ Another study that examined the association between sensory impairment and probable dementia based on an algorithm in the HRS among participants ≥50 years old found no association after adjustment for all covariates.²⁸ In this previous HRS study, the measurement of dementia is based on several cognitive tests, instead of physician diagnosis, which may overestimate the prevalence of dementia, particularly in non-Hispanic Black and Hispanic populations.⁴² Except for the German study and the previous study from the HRS,²⁸ all these results suggest that individuals with dual sensory impairment are at high risk of dementia. In addition to the associations found between dual sensory impairment and dementia (including Alzheimer’s disease), the magnitudes of associations for dual sensory impairment were greater than the product of those for visual impairment only and hearing impairment only (Table 3). Our findings are also consistent with the broader literature on dual sensory impairment in older adults. Studies have found dual sensory loss was associated worse cognitive performance,^23,43 as well as several risk factors of dementia (e.g., depressive symptoms, decline in physical functions, limited mobility).^44–46

Several pathways may explain the observed association between sensory impairment and incident dementia. Factors including degeneration of central nervous structures and cardiovascular diseases are common causes of both sensory impairment and worse cognitive performance.^8,9 Sensory impairment is also associated with higher risk of depression and social isolation, which are risk factors of poor cognitive performance.^10,11,47 Decreased auditory and visual input due to sensory impairment can also result in cognitive deterioration within the brain.⁴⁸ Besides, declined cognition and decreased resources for sensory processing as a result of dementia may lead to declines in sensory performance.⁴⁹

While having visual impairment only was marginally associated with incident dementia, we found significant associations among people <65 years and males, which is consistent with previous studies that found young males had a higher risk of developing dementia than older females among elderly people with visual impairment.^50,51 Visual impairment only was not associated with incident dementia among people aged ≥ 65 years, which probably indicated that sensory impairment in midlife rather than late-life is more likely to accelerate cognitive decline and development of dementia. We did not detect a significant association between hearing impairment only and incident dementia after adjustment for all covariates, although the cumulative incidence rate was higher among individuals with hearing impairment only than those free of sensory impairment. Age may explain the lack of associations in the adjusted model, as it is likely that hearing impairment is a mark of aging.^13,52 Another explanation is that the use of hearing aid could underestimate our self-reported hearing impairment measure, resulting in the lack of associations observed. Moreover, although hearing impairment has been an established risk factor of dementia,⁴ most of the previous studies did not differentiate individuals with hearing impairment only and individuals with dual impairment. Our findings still demonstrate an association between hearing impairment and dementia risk among people with vision impairment.

Although sensory impairment is mostly prevalent among the oldest-old population (ages 85-99 years), our findings on a cohort with younger participants (ages 50-64) would emphasize the importance of early intervention. The associations of sensory impairments among people <65 years were stronger compared to people ≥65 years, and the associations were stronger among females compared to males. Similarly, we found significant associations between dual sensory impairment and incident Alzheimer’s disease among people <65 years, but the associations were not significant among people ≥65 years and either sex group, possibly due to the lack of statistical power. This suggests that sensory impairment at an earlier stage of life is a stronger predictor of dementia compared to that at later life. Hence, early detection and prevention of sensory impairment is particularly important. It also emphasizes the necessity of utilizing age and sex for predicting the risk of dementia, as the prevalence of this disease and sensory impairment differ by age and sex.^52–56 Our findings also emphasize that targeting multiple risk factors simultaneously may reduce the risk of dementia more efficiently. Recently published results from the ACHIEVE trial, a large-scale randomized control trial, showed hearing intervention reduces 3-year cognitive decline among older adults with high risk of dementia aged 70-84 years.⁵⁷ More future studies are expected to evaluate the relationship of improving sensory impairment in midlife and risk of incident dementia.

The study also has several limitations. First, we relied on self-reported data to measure sensory impairments and diagnosis of dementia and Alzheimer’s disease, which could underestimate the prevalence,^52,58 especially for non-Hispanic Blacks and Hispanics populations who often had missed or delayed diagnosis of dementia.⁵⁹ On the other hand, as the HRS was designed to ask participants’ existence of dementia and other serious memory impairment, our dementia measure may include memory loss from non-age-related issues. Future studies are needed to assess the robustness of our findings using objective measures (e.g., Deafblind Severity Index) and actual diagnoses in linked claims or electronic medical records data. Second, due to data limitations, we were not able to examine the association of the duration or severity of sensory impairments with risk of dementia. As sensory impairments can progress overtime,^27,60 these impairments with different level of severity can be associated with different levels of dementia risks, which is expected to be explored in future studies. Additionally, as the sensory impairments were measured at baseline, we did not consider the possible impact of sensory impairments that occurred during our follow-up period. Third, our analysis focuses on perceived sensory impairment rather than biological sensory impairment, and we did not differentiate participants with and without using hearing aid or using glasses. Future research is expected to investigate whether the use of hearing aid and glasses mediate the association between sensory impairments and incident dementia. Fourth, our study does not lead to causal conclusions. While we controlled for a series of covariates in the analysis, potential unmeasured confounding factors (e.g., family history of sensory impairment) may alter the relationship between sensory impairment and incident dementia.

Conclusions

U.S. adults with dual sensory impairment had a particularly greater risk of dementia and Alzheimer’s disease, and the associations were stronger among people <65 years. Targeted screening for dual sensory impairment, or separate screening for visual impairment and hearing impairment may be useful in the prevention of dementia, and future studies are expected to evaluate the effectiveness of improving sensory impairment on the risk of dementia.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Kun Li

Jingkai Wei

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