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 μg/L and 16.4 ± 4.7 μg/L, respectively. In the high frequencies the values were 17.7 ± 6.2 μg/L and 13.1 ± 6.4 μg/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 μg/L and 1.0 ± 0.1 μg/L, respectively. In the high frequencies, the values were 1.0 ± 0.2 μg/L and 0.9 ± 0.3 μg/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.