Glycosylated Hemoglobin Level Is Associated with Hearing Impairment in Older Japanese: The Kurabuchi Study

Objectives To examine the association between glycemic levels (glycosylated hemoglobin (HbA 1c )) and hearing impairment in a general older population. Design Community‐based prospective longitudinal cohort study. Setting Kurabuchi T own, G unma P refecture, J apan. Participants Residents (N = 831; 350 men, 481 women) aged 65 and older were examined in 2005 and 2006 and analyzed in a cross‐sectional study. Residents without hearing impairment at baseline who participated in audiometric re‐examinations 4 years later were analyzed (n = 338). Measurements Hearing impairment was defined as failure to hear a 30‐ dB signal at 1 kHz and a 40‐ dB signal at 4 kHz in the better ear in pure‐tone audiometric tests. Results Mean HbA 1c level ( N ational G lycohemoglobin S tandardization P rogram) was 5.8 ± 0.8% (40 mmol/mol). Odds ratios ( OR s) and 95% confidence intervals ( CI s) of hearing impairment associated with HbA 1c were estimated using a logistic regression model. In the cross‐sectional analysis, HbA 1c levels were positively associated with hearing impairment ( OR per 1.0% increase in HbA 1c  = 1.30, 95% CI  = 1.00−1.68). This association persisted even after excluding 58 participants with a self‐reported history of diagnosed diabetes mellitus. Longitudinal analysis revealed the temporality of the discussed association ( OR  = 1.52, 95% CI  = 1.03−2.23). Conclusion The present study provides supportive evidence for a causal link between hyperglycemia and age‐related hearing loss.