Urinary Caffeine Levels in Chinese Children: Insights from Diet, Gender, and Regional Variations

Abstract

Background/objectives: The consumption of caffeine products among children in China is on the rise, yet there remains a paucity of evidence regarding the variability of caffeine consumption and the influencing factors. Urinary caffeine levels provide a valid indicator of caffeine intake, as it directly reflects the quantitative measure of consumption within the population. This study aimed to investigate the effects of diet, gender, and region on urinary caffeine concentrations in Chinese children and their parents, specifically focusing on participants from Guangdong province and Guangxi province.

Methods: Morning urine samples were pretreated using liquid-liquid extraction. Caffeine and creatinine concentrations were analyzed using ultra-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UPLC-MS/MS), with quality control measures ensuring method accuracy (recovery rate: 92.8-122%, RSD < 20%). Caffeine exposure was assessed through estimated daily intake (EDI) calculations, and statistical analyses, including weighted regression and Spearman correlation, were conducted to evaluate associations with demographic and dietary variables.

Results: The findings revealed that urinary caffeine levels and detection rates among Chinese children were significantly lower than those observed in the United States (30.1 ng/mL), with a median concentration of 2.18 ng/mL and a detection rate of 45%. Urinary caffeine concentrations in males were slightly higher than in females; however, these gender differences were not statistically significant. Certain dietary habits, particularly milk consumption, were found to influence urinary caffeine levels and detection rates. Using the random forest method, urine caffeine detection was highest (nearly 60%) when milk was consumed three times a week. Regionally, children in Guangdong had marginally higher urinary caffeine concentrations compared to those in Guangxi (median: 5.20 μg/g_crea vs. 1.58 μg/g_crea). The estimated daily caffeine intake suggested that children in China consume less caffeine than their counterparts in other countries.

Conclusions: These results indicate that dietary habits significantly correlated with caffeine consumption in children, and urinary caffeine concentration serves as a valuable measure for dietary research.

Keywords: Chinese children; EDI; dietary patterns; regional factors; urinary caffeine.

Figure 1

A violin plot comparing caffeine levels (μg/g_crea) between different sites (Guangxi and Guangdong) (a); (b) groups (children and parents of Guangxi), and (c) genders (male and female children).

Figure 2

Dots of caffeine intake for parents and children in each Guangxi family.

Figure 3

Quantile regression of dietary habits (without direct caffeine intake) and body weight: influence of gender and food consumption over quantiles.

Figure 4

Regression models compared urine caffeine with other factors.

Figure 5

(a) Feature importance (gender and frequency of drinking milk), (b) Partial dependence of frequency of drinking milk, (c) Partial dependence of frequency of gender.

Figure 6

EDI (Estimated Daily Intake) distribution of children (GX—Guangxi, GD—Guangdong).