Preplanned Studies: Hearing Loss and Cognitive Impairment Among Community-Dwelling Older Adults — Liaoning, Henan, and Guangdong Provinces, China, 2019–2020

Hearing loss (HL) and cognitive impairment are both highly prevalent neurological complications for older adults, affecting approximately 59% and 22% of older adults, respectively (1-2). A systematic review and meta-analysis showed that age-related HL was a possible biomarker and modifiable risk factor for cognitive impairment (3). However, to our knowledge, only one study has explored this association among Chinese older adults (4). Therefore, this study aimed to explore the association between HL and cognitive impairment using a large sample, community-based investigation among elderly people. This study utilized data from the second round of the Prevention and Intervention on Neurodegenerative Disease for Elderly in China (PINDEC) project, which was conducted in Liaoning, Henan, and Guangdong provinces in 2019–2020. A total of 10,347 community-dwelling older adults aged 60 years and above were recruited using a stratified, multi-stage cluster sampling method. After adjusting for confounding factors, the multivariate logistic regression analysis showed that, compared with the no HL group, the odds ratios (ORs) for cognitive impairment were 1.23 [95% confidence interval (CI): 1.08, 1.40] for mild HL, 1.55 (95% CI: 1.32, 1.82) for moderate HL, and 1.87 (95% CI: 1.47, 2.39) for severe or profound HL. The association between HL and cognitive impairment highlights the need to integrate the early identification of these problems into primary care, as both are risk factors for healthy aging and potentially preventable and/or treatable conditions.

The PINDEC project was initiated in 2015 to explore the epidemiology of neurodegenerative diseases and other common health problems, and their risk factors, among adults aged 60 years and older in China. The second round of field surveys was conducted from 2019 to 2020 in 12 districts/counties across Liaoning, Henan, and Guangdong provinces. These provinces were selected by considering their geographic location, level of economic development, and degree of aging. A stratified multi-stage cluster sampling method was used to select adults aged 60 years or older who had lived at their residence for more than 6 months in the past year. First, two or three cities in each province were selected by simple random sampling. Second, one county and one district were randomly selected in each city. Third, one township or one street was sampled at each county/district using the proportional to population size (PPS) sampling method. Fourth, cluster sampling was used to select several administrative villages or neighborhood committees in the selected townships/streets, until the survey sample size (1,000 respondents) was met. Trained local health staff conducted interviews and physical examinations with all participants to collect information on demographics, lifestyle, activities of daily living, cognitive function screening, sleep quality, hearing function, and olfactory function.

HL was measured by pure-tone audiometry. Pure-tone audiometry was performed for all individuals in a quiet room in which ambient noise did not exceed 50 dB as measured by a sound level meter. Levels of ambient noise were recorded for each subject in a questionnaire. Each ear was tested separately at 0.5, 1, 2, and 4 kHz to obtain the hearing threshold at each frequency. The average of the hearing thresholds at these four frequencies in the better ear was taken as the pure-tone average (PTA). According to the World Health Organization (WHO) 1997 hearing classification criteria (5), a PTA ≤25 dB was considered normal hearing, 26–40 dB was mild HL, 41–60 dB was moderate HL, and ≥61 dB was severe or profound HL. A uniform type of audiometer in accordance with the national standard GB/T 7341.1-2010 was used for all tests and was calibrated prior to testing. The detailed investigation workflow is shown in Supplementary Figure S1.

Cognitive function was assessed using a Chinese version of the Mini-Mental State Examination (MMSE). Cognitive impairment was defined as an MMSE score of ≤17 for illiterate participants (0 years of education), ≤20 for those with a primary school education (1–6 years of education), and ≤24 for those with a junior high school education and above (≥7 years of education) (6).

Ethical approval was granted by the Ethnics Commitee of the National Center for Chronic and Noncommunicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention (approval number 201902). All the participants provided written informed consent prior to the survey.

A total of 12,369 participants were selected, and 12,223 completed the survey, yielding a response rate of 98.8%. After data cleaning, 1,876 participants were excluded due to incomplete sociodemographic data or lacking responses to the hearing function test or cognitive function screening questions. Finally, a total of 10,347 participants were included in this study. Demographic characteristics of the categorical variables were described as percentages in the overall population and subgroups. The chi-square test was used to analyze differences between subgroups, with a P of <0.05 considered statistically significant. Multivariable logistic regression was used to examine the association of HL with cognitive impairment. All statistical analyses were performed using SAS software (version 9.4; SAS Institute Inc., Cary, USA).

Of the 10,347 participants in the study sample, 57.2% were female, and 58.6% resided in rural areas (Table 1). The average age was 69.1±6.6 years. In 2019–2020, among older adults aged 60 years and above, the prevalence rates of mild HL, moderate HL, and severe or profound HL were 47.2% (95% CI: 46.3%, 48.2%), 18.0% (95% CI: 17.3%, 18.8%), and 4.5% (95% CI: 4.1%, 4.9%), respectively. The prevalence of moderate or higher grades of HL increased with age, from 12.8% at 60–64 years to 52.4% at 80 years and above. Across subgroups, the study found that the prevalence rates of moderate HL and severe or profound HL were likely higher among those residing in rural areas, those of older age, those with fewer years of education, and those who were widowed. There was no statistically significant difference in the prevalence of mild HL between males and females; however, the prevalence rates of moderate HL and severe or profound HL were higher in males than in females (Table 1). The prevalence of cognitive impairment was 19.1% (95% CI: 18.3%, 19.8%) overall and increased gradually with the severity of HL in both males and females (P<0.001) (Figure 1). The prevalence of cognitive impairment was 14.3% (95% CI: 13.1%, 15.5%) for those with normal hearing function, 18.4% (95% CI: 17.3%, 19.5%) for those with mild HL, 25.4% (95% CI: 23.4%, 27.4%) for those with moderate HL, and 32.3% (95% CI: 28.0%, 36.5%) for those with severe or profound HL. Among those with HL, the prevalence of cognitive impairment was higher in females than in males (Figure 1). After adjusting for confounding factors, multivariate logistic regression analysis showed that, compared with the no HL group, the ORs for cognitive impairment were 1.23 (95% CI: 1.08, 1.40) for mild HL, 1.55 (95% CI: 1.32, 1.82) for moderate HL, and 1.87 (95% CI: 1.47, 2.39) for severe or profound HL (Table 2).

Figure 1. 

Prevalence of cognitive impairment among elderly with different grade of HL by genders in Liaoning, Henan, and Guangdong provinces in China, 2019–2020.

Note: P denotes the prevalence difference of cognitive impairment between males and females in each grade of HL among older adults.

Abbreviation: HL=hearing loss.