Correlation between plasma levels of radical scavengers and hearing threshold among elderly subjects with age-related hearing loss

Conclusion: Low plasma melatonin is significant in the development of high frequency hearing loss (HL) among the elderly. Objective: To determine the correlation between hearing threshold and the plasma melatonin and ascorbic acid (vitamin C). Methods: This was a cross-sectional study involving 126 apparently healthy elderly subjects, 59 males and 67 females, aged >60 years. Subjects underwent pure tone audiometry and plasma melatonin and vitamin C were assayed using high-performance liquid chromatography. Results: The mean +/- SD of plasma melatonin among the subjects with normal hearing (NH) (0-30 dB) and those with HL in the speech frequencies was 18.3 +/- 3.6 mu g/L and 16.4 +/- 4.7 mu g/L, respectively. In the high frequencies the values were 17.7 +/- 6.2 mu g/L and 13.1 +/- 6.4 mu g/L for NH and HL, respectively. For vitamin C, the mean +/- SD among subjects with NH and those with HL in the speech frequencies were 1.2 +/- 0.2 mu g/L and 1.0 +/- 0.1 mu g/L, respectively. In the high frequencies, the values were 1.0 +/- 0.2 mu g/L and 0.9 +/- 0.3 mu g/L for NH and HL, respectively. Among subjects with high frequency HL, Spearman's correlation revealed significant correlation between increasing hearing threshold and melatonin (correlation coefficient = -0.30, p = 0.01), but not for vitamin C (correlation coefficient = -0.12, p = 0.22). Linear regression, adjusting for age, still revealed significant correlation between the melatonin (correlation coefficient = -0.03, p = 0.00) and hearing threshold in the high frequencies.