Plasma Glial Cell-Derived Neurotrophic Factor and Insulin-like Growth Factor-1 Levels Were Not Correlated with the Severity of Age-Related Hearing Impairment in Humans.

The relationship between plasma glial cell-derived neurotrophic factor (GDNF) or insulin-like growth factor-1 (IGF-1) levels and age-related hearing impairment (ARHI) has not been reported in humans. By cross-sectional design, 268 subjects older than 33, with normal cognitive function and normal or symmetric sensorineural hearing loss, were selected randomly. Multivariate linear regression analysis was performed to test the impact of the plasma GDNF or IGF-1 level on the pure tone threshold of low frequencies (PTA-low) and high frequencies (PTA-high), respectively. Results showed that plasma GDNF and IGF-1 levels decreased with age without statistical significance. Multivariate linear regression analysis showed that GDNF or IGF-1 levels were not significantly correlated with PTA-low or PTA-high after adjusting age, gender, body mass index, systemic diseases, habits, and noise exposure. In conclusion, plasma GDNF or IGF-1 levels were not associated with the severity of ARHI in humans. However, these findings did not support the roles of GDNF or IGF-1 genotypes on hearing.