Blood levels of nicotinic acid negatively correlate with hearing ability in healthy older men

Abstract Background Age-related hearing loss (ARHL) is a common phenomenon observed during aging. On the other hand, the decrease in Nicotinamide adenine dinucleotide (NAD +) levels is reported to be closely related to the age-related declines in physiological functions such as ARHL in animal studies. Moreover, preclinical studies confirmed NAD + replenishment effectively prevents the onset of age-related diseases. However, there is a paucity of studies on the relationship between NAD+ metabolism and ARHL in humans. Methods This study was analyzed the baseline results of our previous clinical trial, in which nicotinamide mononucleotide or placebo was administered to 42 older men (Igarashi et al., NPJ Aging 8:5, 2022). The correlations between blood levels of NAD+-related metabolites at baseline and pure-tone hearing thresholds at different frequencies (125, 250, 500, 1000, 2000, 4000, and 8000 Hz) in 42 healthy Japanese men aged > 65 years were analyzed using Spearman’s rank correlation. Multiple linear regression analysis was performed with hearing thresholds as the dependent variable and age and NAD+-related metabolite levels as independent variables. Results Positive associations were observed between levels of nicotinic acid (NA, a NAD+ precursor in the Preiss-Handler pathway) and right- or left-ear hearing thresholds at frequencies of 1000 Hz (right: r = 0.480, p = 0.001; left: r = 0.422, p = 0.003), 2000 Hz (right: r = 0.507, p