Monitoring caffeine intake in children with a questionnaire and urine collection: a cross-sectional study in a convenience sample in Switzerland.

PURPOSE The objectives of this study were (1) to estimate caffeine intake and identify the main sources of intake using a dietary questionnaire, (2) to assess 24-h urinary excretion of caffeine and its metabolites, and (3) to assess how self-reported intake estimates correlates with urinary excretion among children in Switzerland. METHODS We conducted a cross-sectional study of children between 6 and 16 years of age in one region of Switzerland. The participants filled in a dietary questionnaire and collected a 24-h urine sample. Caffeine intake was estimated with the questionnaire. Caffeine, paraxanthine, theophylline, and theobromine excretions were measured in the urine sample. Correlations between questionnaire-based intake and urinary excretion estimates were assessed using Spearman correlation coefficients. RESULTS Ninety-one children were included in the analysis (mean age 10.6 years; 43% female). The mean daily caffeine intake estimate derived from the diet questionnaire was 39 mg (range 0-237), corresponding, when related to body weight, to 1.2 mg/kg (range 0.0-6.3). Seven children (8%) had a caffeine intake above the upper recommended level of 3 mg/kg per day. The main sources of caffeine intake were cocoa milk (29%), chocolate (25%), soft drinks (11%), mocha yogurt (10%), tea (8%), and energy drinks (8%). The 24-h urinary excretion of caffeine was 0.3 mg (range 0.0-1.5), paraxanthine 1.4 mg (range 0.0-7.1), theophylline 0.1 mg (range 0.0-0.6), and theobromine 14.8 mg (range 0.3-59.9). The correlations between estimates of caffeine intake and the 24-h urinary excretion of caffeine was modest (ρ = 0.21, p = 0.046) and with the metabolites of caffeine were weak (ρ = 0.09-0.11, p = 0.288-0.423). CONCLUSIONS Caffeine intake in a sample of children in a region of Switzerland was relatively low. The major sources of intake were cocoa milk, chocolate and soft drinks. Self-reported caffeine intake correlated weakly with urinary excretion of caffeine and some of its main metabolites. TRIAL REGISTRATION NUMBER NCT02900261