L-Shaped Association Between Dietary Copper Intake and Chronic Obstructive Pulmonary Disease Among American Adults: Findings From the National Health and Nutrition Examination Survey 1999–2018

Abstract

Background

Copper plays a vital role in human physiological functions. However, limited epidemiologic evidence exists for an association between dietary copper intake and chronic obstructive pulmonary disease (COPD).

Objectives

This study aimed to assess the association between dietary copper intake and COPD in American adults.

Design

This cross-sectional study used data from the US National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018.

Participants/setting

Following the inclusion criteria, data from a total of 39 644 adults aged 20 and older were included in this study, out of which 3159 individuals had been diagnosed with COPD by a health care provider.

Main outcome measures

Dietary data were obtained through 24-hour dietary recall, and COPD diagnosis information was derived from a standardized medical condition questionnaire.

Statistical analyses performed

Multivariable logistic regression analysis was conducted to explore the association between dietary copper intake and COPD. To assess the dose–response relationship, a 3-piecewise restricted cubic spline analysis was employed. Potential thresholds were identified with a 2-piecewise logistic regression model. Subgroup analysis was performed to assess heterogeneity and explore potential interactions.

Results

Compared with individuals in the lowest tertile of dietary copper intake (T1, <0.89 mg/day), those in the highest tertile (T3, >1.35 mg/day) had an adjusted odds ratio (OR) of 0.79 for COPD (95% confidence interval [CI], 0.68–0.92, P = .002). The relationship between dietary copper intake and COPD followed a nonlinear L-shaped curve (P < .001). Threshold analysis found a statistically significant inverse association between dietary copper intake and the odds of COPD for intakes < 1.5 mg/day but no significant association for intakes ≥ 1.5 mg/day. Subgroup analysis indicated an interaction effect with age.

Conclusions

An L-shaped inverse association was observed between dietary copper intake and COPD in US adults, at a threshold of approximately 1.5 mg/day, with an observed age interaction.