Work

Spot urine sampling yields reliable measurements for urine caffeine and caffeine metabolites over short-to-intermediate timeframes in a regional cohort of 50 United States adults

Year: 2025

Type: article

Abstract: BACKGROUND: The temporal variability of caffeine and caffeine metabolite concentrations in spot urine samples is unknown. Understanding this variability in both unadjusted and flow-adjusted measurements is essential to assess the suitability of spot urine sampling for measuring these compounds and estimate the number of samples required for reliable measurements. OBJECTIVES: This study aimed to examine the temporal variability of unadjusted and flow-adjusted concentrations of caffeine and its metabolites in spot urine samples, both within and between individuals, over short-to-intermediate timeframes. METHODS: We measured urine caffeine and 14 caffeine metabolite concentrations in 1749 spot samples collected from a cohort of 50 adults over a 6-wk period from the Pilot Study to Estimate Human Exposures to Pyrethroids using an Exposure Reconstruction Approach. We calculated between- and within-person variances, 95%-fold ranges, and intraclass correlation coefficients (ICCs) for unadjusted, flow rate-, creatinine-, and specific gravity-adjusted analyte concentrations over timeframes of 24 h, 1 wk, and 6 wk. Additionally, we estimated the number of spot urine samples needed for reliable measurements (ICC ≥ 0.80). RESULTS: We found that ICCs were the highest in the 24-h timeframe, with 69% of analyte × urine flow adjustment combinations yielding median ICCs ≥0.80 (range: 0.62-0.94). ICCs decreased as the timeframe increased (1-wk median ICC range: 0.49-0.84; 6-wk ICC range: 0.37-0.76). Caffeine showed no ICC improvement with urine flow adjustments, whereas dimethylxanthines showed mixed results. Later-forming metabolites consistently showed ICC improvement across all types of urine flow adjustments. CONCLUSIONS: Overall, 1-2 spot urine samples were sufficient to obtain a reliable concentration estimate (ICC ≥ 0.80) for caffeine and most caffeine metabolites during 24-h or 1-wk sampling timeframes with appropriate urine flow adjustment, with 2-3 spot urine samples being sufficient for sampling over 6 wk.

Source: American Journal of Clinical Nutrition

DOI: 10.1016/j.ajcnut.2025.09.022

Authors: Michael E Rybak, Maya R Sternberg, Patrick W Simon, Marsha K Morgan

Institutions: Centers for Disease Control and Prevention, National Center for Environmental Health, Environmental Protection Agency

Language: English

Topic: Coffee research and impacts

Subfield: Pharmacology

Field: Medicine

Domain: Health Sciences

SDG: Good health and well-being

Open Access status: hybrid

Estimated APC paid: $5,200