Principal Components Analysis of Spot Urine Caffeine and Caffeine Metabolites Identifies Promising Exposure Biomarkers of Caffeine and Theobromine Intake in a Cross-Sectional Survey of the United States Population (National Health and Nutrition Examination Survey 2009-2014).

BACKGROUND

Spot urine concentrations of caffeine and certain caffeine metabolites correlate well with 24-h caffeine intake and have potential use as caffeine exposure biomarkers. However, a high degree of intercorrelation exists among these urine compounds, and their correlations with intake are very similar, making the selection of a single intake biomarker challenging based on bivariate analyses alone.

OBJECTIVES

To use principal components (PCs) analysis (PCA) as a dimensionality reduction tool to identify underlying correlation structures in the relationship of caffeine intake with spot urine caffeine and caffeine metabolite concentrations.

METHODS

We performed weighted bivariate analyses and a weighted PCA of spot urine concentrations of caffeine and 14 caffeine metabolites, and 24-h intakes of caffeine (foods, beverages, and supplements) and theobromine (foods and beverages) from 7732 participants ≥6 y in the National Health and Nutrition Examination Survey (NHANES) 2009-2014.

RESULTS

Bivariate analyses revealed intercorrelation patterns that effectively divided the urine analytes into 2 groups based on their association with either caffeine or theobromine intake. PCA yielded 2 components (PC1 and PC2) that accounted for 83.0% of the total variance. PC1 (70.9%) showed a positive correlation with all original variables and approximated a weighted sum related to the urine analyte concentrations in the original data. PC2 (12.1%) yielded 2 clusters of correlated variables resembling a weighted contrast of the caffeine and theobromine intake associations observed in the original data. Urine 1-methylxanthine showed the strongest PCA correlation with caffeine intake, followed by 5-acetylamino-6-amino-3-methyluracil, 1-methyluric acid, and 1,7-dimethyluric acid. Urine theobromine and its downstream metabolites showed PCA correlation primarily with theobromine intake, though correlation with caffeine intake was also evident.

CONCLUSIONS

With PCA, we were able to identify an underlying correlation structure in the NHANES 2009-2014 data that revealed promising urine exposure biomarkers of caffeine and theobromine intake.