Table 1.
Characteristics of cohort studies included in the systematic review and meta-analysis (n = 10)
| Study | Country | Sample size, n | Follow-up, years | Age, years | Female, % | Assessment of HI | Definition of MCI/dementia | Results | Covariates |
|---|---|---|---|---|---|---|---|---|---|
| Framingham Heart Study Gates, 2002 [16] | USA | 740 | Mean: 8.4 (range: 3–12) | Normal hearing: 71.7±4.9 HI: 77.8±5.2 |
Normal hearing: 61.4 HI: 53.3 | A central auditory speech-processing deficit was defined as a score of 50% or less correct on the Synthetic Sentence Identification with Ipsilateral Competing Message Test in at least one ear with normal word recognition ability in both ears Prevalence: 2.0% | The diagnosis of probable Alzheimer disease was made prospectively using the NINCDS-ADRDA criteria | Alzheimer's dementia (n = 40): RR = 23.3, 95% CI: 6.6, 82.7 | Age, gender, education level, apolipoprotein allele E4 presence, and hearing level |
| Baltimore Longitudinal Study of Aging Lin, 2011 [17] | USA | 639 | Median: 11.9 | By HL status: Normal: 59.9±12.2 Mild: 71.1±8.6 Moderate: 77.0±8.4 Severe: 77.7±4.8 |
By HL status: Normal: 50.5 Mild: 24.8 Moderate: 32.1 Severe: 16.7 |
HL was defined by a pure-tone average of hearing thresholds at 0.5, 1, 2, and 4 kHz in the better-hearing ear (normal, <25 dB; mild loss, 25–40 dB; moderate loss, 41–70 dB; and severe loss, >70 dB) Prevalence: 28.8% | Dementia: by consensus diagnostic conference | All-cause dementia (n = 58): Mild HI: HR = 1.89, 95% CI: 1.00, 3.58; Moderate HI: HR = 3.00, 95% CI: 1.43, 6.30; Severe HI: HR = 4.94, 95% CI: 1.09, 22.40 Alzheimer's dementia (n = 37): per 10 dB of HL: HR = 1.27, 95% CI: 1.06, 1.50 |
Sex, age, race, education, diabetes mellitus, smoking, and hypertension |
| Adult Changes in Thought Gates, 2011 [18] | USA | 274 | Mean: 2.2 (range: 0.8–4) | Mean: 80 (range: 71–96) | 62.8 | With severe CAD: SSI-ICM: <50% correct DSI: <50% correct DDT: <50% correct With moderate CAD: SSI-ICM: <80% correct DSI: <80% correct DDT: <80% correct Prevalence: 16.1% |
Alzheimer's dementia: physician diagnosis according to NINCDS-ADRDA criteria | Alzheimer's dementia (n = 21): With severe CAD: By DSI <50%: HR =9.9, 95% CI: 3.6, 26.7 By DDT <50%: HR= 2.2, 95% CI: 0.7, 7.0 By SSI-CCM <50%: HR = 2.1, 95% CI: 0.7, 6.6 With moderate CAD: By DSI <80%: HR = 6.8, 95% CI: 1.9, 24.1; By DDT <80%: HR = 7.0, 95% CI: 1.6, 31.0; By SSI-CCM <80%: HR = 2.5, 95% CI: 0.9, 7.5 |
Education |
| Caerphilly Prospective Study Gallacher, 2012 [19] | UK | 1,057 | Mean: 16.8 (range: 14.5–19.8) | Mean: 56.1±4.4 | 0 | Pure-tone unaided audiometric threshold assessed at 0.5, 1, 2, and 4 KHz at baseline and after 9 years Prevalence: 43.2% | Dementia (Alzheimer's and vascular) DSM-IV criteria | All-cause dementia (n = 79): OR = 2.67, 95% CI: 1.38, 5.18 Vascular dementia (n = 38): OR = 2.40, 95% CI: 0.99, 5.83 Nonvascular dementia (n = 41): OR = 2.96, 95% CI: 1.21, 7.22 MCI (n = 146): OR = 1.24, 95% CI: 0.77, 2.01 |
Age, social class, anxiety, premorbid intelligence |
| Health ABC study Lin, 2013 [20] | USA | 1,984 | 6 | Mean: 77.4 | By hearing status: Normal: 62.3 HL: 44.8 | Pure-tone average: mild loss, 25–40 dB; moderate loss, 41–70 dB; and severe loss, >70 dB Prevalence: 58.6% | 3MS score of less than 80 or a decline in 3MS score of more than 5 points from baseline | MCI (n = 609): Overall: HR = 1.24, 95% CI: 1.05, 1.48 Mild HL: HR = 1.19, 95% CI: 0.99, 1.44 Moderate HL or above: HR = 1.36, 95% CI: 1.08, 1.70 Per 10 dB of HL: HR = 1.07, 95% CI: 1.01, 1.14 |
Age, sex, race/ethnicity, education, study site, smoking status, hypertension, diabetes mellitus, and stroke history |
| Deal, 2017 [21] | USA | 1,889 | 9 | Mean: 75.5±3 (range: 70–79) | 53 | A pure-tone average in decibels hearing level (dBHL) was calculated in the better hearing ear using thresholds from 0.5 to 4 kHz, and HI was defined as normal hearing (≤25 dBHL), mild (26–40 dBHL), and moderate/severe (>40 dBHL) Prevalence: 58.4% | Dementia was defined using a prespecified algorithm incorporating medication use, hospital records, and neurocognitive test scores | Dementia (n = 229): Mild HI: HR = 1.02, 95% CI: 0.75, 1.40 Moderate/severe HI: HR = 1.55, 95% CI: 1.10, 2.19 Per 10 dB increase: HR = 1.14, 95% CI: 1.03, 1.26 |
Age, sex, race, education, study site, smoking status, hypertension, diabetes, and stroke |
| Cache County Study on Memory, Health, and Aging Gurgel, 2014 [22] | USA | 4,463 | By hearing status: Normal: 6.08 HL: 4.32 |
Mean: 75.4 (range: 65.3–102.4) | 57.0 | Subjects with at least one testing item coded with auditory impairment were then coded in a dichotomous indicator as HL present or absent Prevalence: 18.7% | Diagnoses of dementia were based on DSM-III-R criteria | Dementia (n = 72): HR = 1.27, 95% CI: 1.03, 1.56 | Sex, presence of APOE-4 allele, education, baseline age, cardiovascular risk factors |
| Epidemiology of Hearing Loss Study Fischer, 2016 [23] | USA | 1,884 | 10 | Mean: 66.7±8.4 | 59.1 | HI was a pure-tone average of hearing thresholds (0.5, 1, 2, 4 kHz) of >25 dB hearing level in either ear Prevalence: 43.8% | Cognitive impairment was defined as a Mini-Mental State Examination score of <24 or history of dementia or Alzheimer disease | MCI (n = 145): HR = 1.90, 95% CI: 1.11, 3.26 | Age, sex, education, smoking, BMI, exercise, alcohol consumption, hypertension, diabetes, high inflammatory markers, non-HDL, intima-media thickness, frailty score, longest held job, cold or stuffy nose, nasal polyps, deviated septum, allergies, head injury, stroke or TIA, epilepsy |
| Washington Heights-Inwood Columbia Aging Golub, 2017 [24] | USA | 1,881 | Mean: 7.4±4.6 (range: 0.9–22) | Mean: 75.8±6.3 | 70 | Hearing normal vs. abnormal, hearing normal versus abnormal (repeat of first variable occurring later during the visit), no impairment in hearing versus some difficulty hearing versus must speak loudly versus must shout versus cannot rate, auditory ability adequate versus inadequate, has hearing aid; if any HL was noticed among any of the variables that assessed HL, or if the subject wore hearing aids, OHL was considered present Prevalence: 10.8% | A neuropsychological battery was administered at baseline and all follow-up visits; dementia was then diagnosed using previously defined cutoff scores decided in a consensus panel of neurologists, neuropsychologists, and psychiatrists | Dementia (n = 377): HR = 1.69, 95% CI: 1.3, 2.3 Alzheimer disease: HR = 1.85, 95% CI: 1.3, 2.6 Vascular dementia: HR = 1.34, 95% CI: 0.5, 3.5 |
Age, sex, ethnicity, race, years of education, diabetes mellitus, hypertension, heart disease, smoking, APOE4 genotype, and stroke |
| Singapore Longitudinal Ageing Study Heywood, 2017 [25] | Singapore | 2,599 | Median: 3.8 | ≥55 | 63.8 | Hearing was tested at a study site by a research nurse using the whispered voice test in a standard manner Prevalence: 2.7% | MMSE ≤23 or neuropsychological domain scores below 2 SD of age- and education-adjusted mean and evidence of social or occupational function impairment (dependency in 1 or more basic ADL or CDR score ≥1) | MCI (n = 144): HR = 1.85, 95% CI: 0.78, 4.40 | Sex, age, ethnicity, education, central obesity, hypertension, diabetes, dyslipidemia, smoking, alcohol, leisure time activity, cardiac diseases, depressive symptoms |
MCI, mild cognitive impairment; RR, risk ratio; HR, hazard ratio; OR, odds ratio; HI, hearing impairment; HL, hearing loss; OHL, observed hearing loss; NINCDS-ADRDA, National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association; 3MS score, Modified Mini-Mental State score; MMSE, Mini-Mental State Examination; DSM, Diagnostic and Statistical Manual; SSI-ICM, Synthetic Sentence Identification with Ipsilateral Competing Message; DSI, Dichotic Sentence Identification Test; DDT, Dichotic Digits Test; CAD, central auditory dysfunction; BMI, body mass index; HDL, high-density lipoprotein; TIA, transient ischemic attack.