Table 1.

Principal case-control and longitudinal population-based studies of peripheral auditory dysfunction and central auditory processing dysfunction in age-related hearing impairment in relation to late-life cognitive decline, incident dementia and Alzheimer's disease (AD).

References	Subjects	Assessment of auditory function	Assessment of cognition or diagnosis of dementia	Covariates	Principal findings
PERIPHERAL AUDITORY DYSFUNCTION
Anstey et al., 2001 The Australian Longitudinal Study of Aging Australia	2087 subjects aged 70–96 years	Pure-tone audiometry with portable audiometers	Similarities and DSS from WAIS-R, BNT, and NART	Age	In a 2-year follow-up, decline in hearing was not associated with decline in any cognitive domain
Anstey et al., 2003 The Australian Longitudinal Study of Aging Australia	525 subjects, mean age 74.7 years	Pure-tone audiometry with portable audiometers	Similarities and DSS from WAIS-R, BNT, and NART	Age, gender, depressive symptoms, self-rated health, and medical comorbidities	In a 8-year follow-up, a weak association between hearing decline and memory decline was found
Lin et al., 2004 The Study of Osteoporotic Fractures (SOF) USA	6112 women aged 69 years and older	Pure-tone audiometry with hand-held audiometers	3MS and functional status assessed with five activities: walking, climbing stairs, preparing meals, shopping, and doing housework	Medical comorbidities, age, education level, smoking, presence of vertebral fracture, benzodiazepine use, BMI, Lubben social network, grip strength, walking speed, and baseline cognitive or functional status	Combined hearing and vision impairment was associated with cognitive and functional decline after a 4-year follow-up period
Valentijn et al., 2005 The Maastricht Aging Study The Netherlands	418 subjects aged 55 years and older	Pure-tone audiometry	VVLT, SCWT, CST, VFT, and LDST	Age, sex, education level, baseline cognitive performance, change in vision or hearing, and baseline vision or hearing	A change in auditory acuity predicted change in memory performance, and auditory acuity at baseline predicted change in the mean score of the first two SCWT cards and the LDST in a 6-year follow-up
Wallhagen et al., 2008 The Alameda County Study USA	2002 subjects aged 50–94 years	Self-report	A self-report measure of cognitive functioning	Chronic conditions, age, sex, and education level	In a 5-year follow-up, a relationship between baseline hearing impairment and subsequent poorer cognitive function was found in both existing and new cases of cognitive impairment
Lin et al., 2011 The Baltimore Longitudinal Study of Aging USA	639 subjects aged 36–90 years	Pure-tone audiometry	Diagnoses of dementia and AD using DSM-III-R and NINCDS-ADRDA criteria	Sex, age, race, education level, diabetes, smoking, hypertension, and hearing aid use	During a median follow-up of 11.9 years, baseline hearing loss was independently associated with incident all-cause dementia
Gallacher et al., 2012 The Caerphilly cohort United Kingdom	1057 men mean age 56.2 years	Pure-tone audiometry.	Diagnoses of dementia and AD using DSM-IV and NINCDS-ADRDA criteria. MMSE, CAMCOG, AH4, and CRT	Age, social class, anxiety, and premorbid cognitive ability	Over a 17-year period, auditory threshold was found to be associated with incident dementia and cognitive decline. An additional effect of change in auditory threshold over 8 years was found for nonvascular dementia
Kiely et al., 2012 The Dynamic Analyses to Optimize Aging Project Australia	4221 subjects aged 50–103 years	Pure-tone audiometry.	MMSE	Age, sex, diabetes, stroke, hypertension, visual impairment, smoking status, workplace noise exposure, and high-frequency audiometric noise notches	Cognitive impairment and hypertension were independently associated with lower levels and accelerated declines of peripheral hearing, and incidence of cognitive impairment was also associated with poorer hearing function in a 11-year follow-up
Lin et al., 2013 The Health ABC Study USA	1984 subjects mean age: 77.4 Years	Pure-tone audiometry.	3MS and DSS	Age, sex, race/ethnicity, education level, study site, smoking status, hypertension, diabetes mellitus, and stroke history	In a 6-year follow-up, hearing loss was independently associated with accelerated cognitive decline and incident cognitive impairment
CENTRAL AUDITORY PROCESSING DYSFUNCTION
Gennis et al., 1991 USA	112 community-dwelling adults aged 60 years and older	Pure-tone audiometry and SPIN	WMS and JCST	Age and sex	In a 5-years follow-up, no evidence that peripheral or central hearing impairment predicted cognitive decline was found
Gates et al., 1996 Framingham Heart study USA	Population-based, 1662 people aged 63–95 years	Pure-tone audiometry and SSI-ICM	MMSE and diagnosis of dementia and AD using NINCDS-ADRDA criteria	Age and education level	In a 6-year follow-up, CAP dysfunction in one ear increased the risk of subsequent dementia or cognitive decline; CAP deficit present in both ears doubled the risk
Gates et al., 2002 Framingham Heart study USA	Population-based, 740 people aged 63–95 years	Pure-tone audiometry and SSI-ICM	MMSE and diagnosis of probable AD using NINCDS-ADRDA criteria	Age, gender, education level, APOE e4 allele presence, and hearing level	In a 8-year follow-up, CAP dysfunction presence was associated with a 10 times higher risk for developing AD
Gates et al., 2011 The Adult Changes in Thought Study USA	Population-based, 274 people aged 71–96 years	Pure-tone audiometry, SSI-ICM, DSI test, and DDT	CASI and diagnoses of dementia and AD using DSM-IV and NINCDS-ADRDA criteria	Education level	In a 3-year follow-up, severe CAP dysfunction strongly predicted the risk of a subsequent diagnosis of AD
Idrizbegovic et al., 2013 Sweden	Case-control, 70 participants aged 50–80 years with MCI or AD and SMC	Pure-tone audiometry, SPIN, and DDT	MMSE, MCI diagnosis, and diagnoses of dementia and AD using DSM-IV and NINCDS-ADRDA criteria	None	In a 1.5-year follow-up, CAP showed a significant decline in the AD group compared with the controls/SMC subjects (left ear)

DSS, Digit Symbol Substitution subscale; WAIS-R, Wechsler Adult Intelligence Scale-revised; BNT, Boston Naming Test; NART, National Adult Reading Test; 3MS, modified version of Mini-Mental State Examination; BMI, body mass index; VVLT, Visual Verbal Learning Test; SCWT, Stroop Color Word Test; CST, Concept Shifting Task; VFT, Verbal Fluency Test; LDST, Letter-Digit Substitution Test; DSM-III-R, Diagnostic and Statistical Manual of Mental Disorders, third edition, revised; NINCDS-ADRDA, National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association; MMSE, Mini-Mental State Examination; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition; CAMCOG, Cambridge Cognitive Examination; AH4, Alice Heim test; CRT, 4-choice reaction time task; SPIN, Speech perception in noise; WMS, Wechsler Memory Scale; JCST, Jacobs Cognitive Screening Test; SSI-ICM, Synthetic sentence identification with either an ipsilateral competing message; APOE, apolipoprotein E; DSI, dichotic sentence identification; DDT, dichotic digits test; CASI, Cognitive Abilities Screening Instrument; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition; MCI, mild cognitive impairment; SMC, subjective memory complaints.