Association between dietary copper intake and cognitive function in American older adults: NHANES 2011-2014

Abstract

This cross-sectional observational study examined the association between dietary copper intake and cognitive function in American older adults, using data from the 2011 to 2014 National Health and Nutrition Examination Survey (NHANES). Analyzing a total of 2420 participants, dietary copper intake was determined by averaging two 24-h dietary recalls, whereas cognitive function was assessed by the Digit Symbol Substitution Test (DSST), the Animal Fluency Test (AFT), a Consortium to Establish a Registry for Alzheimer's disease (CERAD) subtest and global cognition Z score. Multivariate linear regression models were used to explore the association between copper levels and cognitive function. Higher copper intake was associated with higher cognitive scores. In the fully adjusted model, compared to the lowest quartile (Q1), the highest quartile (Q4) of copper intake was associated with related to higher cognitive scores (DSST: β = 3.80, 95% CI 1.90,5.70; AFT: β = 1.23, 95% CI 0.48,1.99; CERAD-IRT: β = 0.58, 95% CI - 0.06,1.22; CERAD-DRT: β = 0.47, 95% CI 0.15,0.80; Z score: β = 0.20, 95% CI 0.10,0.29), particularly in participants with a history of stroke. Multivariate smooth spline analysis revealed that dietary copper intake was related to DSST, AFT and Z score in an inverted L-shaped nonlinear manner. The inflection point of copper was 1.63 mg/day for DSST, 1.42 mg/day for AFT and 1.22 mg/day for the Z score. Further longitudinal research is necessary to substantiate these findings.

Fig. 1

Flow chart of the screening and enrollment of study participants.

Fig. 2

Association between dietary copper intake and cognitive performance in CERAD-IRT, CERAD-DRT, DSST, AFT and Z score. Solid and dashed lines represent the predicted value and 95% confidence intervals. Adjusted for age, gender, race/ethnicity, poverty income ratio, marital status, education level, body mass index, smoking status, alcohol status, hypertension, diabetes mellitus, cardiovascular disease history, stroke, energy, zinc, iron, selenium, fat, and total saturated fatty acids. Only 99% of the data is shown. DSST, Digit Symbol substation test AFT, Animal Fluency Test; CERAD, Consortium to Establish a Registry for Alzheimer’s disease; CERAD-IRT, immediate recall in CERAD trial; CERAD-DRT, delayed recall in CERAD trial; Z score is average of the standardized scores of DSST, AFT, CERAD-IRT, CERAD-DRT.

Fig. 3

Stratified analyses of the association between cognitive performance and dietary copper intake according to baseline characteristics in Z score test. Note: The P value for interaction represents the likelihood of interaction between the variable and copper. CI confidence interval.