The Association of Copper Intake with Hearing Loss: a Cross-Sectional Study.

Currently, evidence for the relationship between copper intake and hearing loss (HL) is insufficient; therefore, further research is needed. This study aimed to investigate the potential association between copper intake and HL in adults in the United States. We conducted a retrospective cross-sectional study using data from 2777 participants of the 2015-2016 National Health and Nutrition Examination Survey (NHANES). Measurements of copper intake and HL were collected for all participants. Multivariate logistic regression, restricted cubic spline, and subgroup analyses were used to assess the research objectives. In fully adjusted Model 3, continuous dietary copper intake was inversely associated with speech-frequency hearing loss (SFHL, OR = 0.71, 95%CI:0.55-0.91, p = 0.008) and high-frequency hearing loss (HFHL, OR = 0.74, 95%CI:0.60-0.91, p = 0.004). Relative to Q1, Q3 and Q4 showed significant inverse associations with SFHL; significant inverse associations with HFHL were found in Q2 and Q4 rather than Q3. Significant linear trends across quartiles existed for both outcomes (Table 2). Subgroup analyses indicated significant sex interaction for SFHL (p = 0.023). Significant inverse associations between copper intake and two types of hearing loss were only observed in females. Heterogeneous associations were found across subgroups stratified by age, chronic disease and noise exposure, with most interaction terms non-significant (Table 3, Fig. 3). Restricted cubic spline models demonstrated no statistically significant nonlinear association between dietary copper intake and either SFHL (p for non-linearity = 0.328) or HFHL (p for non-linearity = 0.616) (Fig. 2). Our findings suggested an inverse linear association between dietary copper intake and hearing loss among US adults, and this association was modified by sex, being statistically significant only in females. Further research is needed to explore the underlying mechanisms.