Discussion
The relationship between NADIn this study, we observed a negative correlation between concentrations of NA, an NADInterestingly, the relationships between NA levels and hearing thresholds were most evident at 1000 and 2000 Hz, which tend to be less elevated with age than the higher frequencies [We did not observe any correlation between whole-blood levels of NADThis study has several limitations. This study was sub-analysis, and the sample size was not pre-calculated for this correlation analysis. Although some correlations might be undetectable due to the small sample size in our analysis, post-hoc power calculation for spearman’s rank correlation showed that the sample size was enough to detect the moderate or strong correlations (power = 0.900 (correlation coefficient = 0.5), and power = 0.702 (correlation coefficient = 0.4)). Additionally, participants comprised healthy Japanese men aged 65 years or older. The results may be relevant only for the certain healthy older Japanese men. Further investigations including other races, generation, and gender are warranted. Moreover, as all analyses were exploratory, multiple comparisons were not performed. However, the significant correlation between NA levels and hearing ability were observed at the same frequencies (1000 and 2000 Hz) on both ear sides in our analyses. While this consistency is not explained by false positive results, we consider our findings deserves further investigation to confirm our findings. Finally, the mechanism of ARHL requires further elucidation from the perspective of the NADIn conclusion, we report a negative correlation between whole-blood concentrations of NA and hearing ability. The relevance of NAD