Question Is the association between hearing and cognition present among individuals who have classically defined normal hearing levels?
Findings In this cross-sectional study of 6451 individuals, there was an inverse association between decreasing hearing and decreasing cognition among those classically defined as having normal hearing, after adjusting for confounders.
Meaning The findings suggest that the association between hearing loss and impaired cognition may be present at earlier levels of hearing loss than previously recognized; the current 25-dB threshold for defining adult hearing loss may be too high.
Importance Age-related hearing loss (HL) is a common and treatable condition that has been associated with cognitive impairment. The level of hearing at which this association begins has not been studied to date.
Objective To investigate whether the association between hearing and cognition is present among individuals traditionally classified as having normal hearing.
Design, Setting, and Participants Cross-sectional study of 2 US epidemiologic studies (Hispanic Community Health Study [HCHS], 2008-2011, and National Health and Nutrition Examination Study [NHANES], 1999-2000, 2001-2002, and 2011-2012 cycles). The dates of analysis were November 2018 to August 2019. Multivariable generalized additive model (GAM) regression and linear regression were used to assess the association between HL (exposure) and cognition (outcome). Participants included 6451 individuals aged 50 years or older from the general Hispanic population (HCHS [n = 5190]) and the general civilian, noninstitutionalized US population (NHANES [n = 1261]).
Exposures Audiometric HL (4-frequency pure-tone average).
Main Outcomes and Measures Neurocognitive performance measured by the Digit Symbol Substitution Test (DSST) (score range, 0-113), Word Frequency Test (range, 0-49), Spanish-English Verbal Learning Test (SEVLT) 3 trials (range, 5-40), SEVLT recall (range, 0-15), and Six-Item Screener (range, 0-6); higher scores indicated better cognitive performance.
Results Among 6451 individuals, the mean (SD) age was 59.4 (6.1) years, and 3841 (59.5%) were women. The GAM regression showed a significant inverse association between hearing and cognition across the entire spectrum of hearing after adjusting for demographics and cardiovascular disease. In separate multivariable linear regressions stratified by the classic binary definition of HL, decreased hearing was independently associated with decreased cognition in adults with normal hearing (pure-tone average ≤25 dB) across all cognitive tests in the HCHS. For example in this group, a 10-dB decrease in hearing was associated with a clinically meaningful 1.97-point (95% CI, 1.18-2.75) decrease in score on the DSST. When using a stricter HL cut point (15 dB), an association was also present in NHANES. The associations between hearing and cognition were stronger or equivalent in individuals with normal hearing than among those with HL. For example, there was a 2.28-point (95% CI, 1.56-3.00) combined cohort DSST score decrease per 10-dB decrease among individuals with normal hearing vs a 0.97-point (95% CI, 0.20-1.75) decrease among those with HL, with a significant interaction term between continuous and binary hearing.
Conclusions and Relevance An independent association was observed between cognition and subclinical HL. The association between hearing and cognition may be present earlier in HL than previously understood. Studies investigating whether treating HL can prevent impaired cognition and dementia should consider a lower threshold for defining HL than the current 25-dB threshold.