AbstractIn experimental and clinical studies, green or black tea consumption has been shown to reduce oxidative stress. However, these studies involved high levels of tea consumption and may not reflect patterns in the general population. Here, we examined the association between black or green tea consumption and oxidative stress in a cross-sectional study of 889 premenopausal US women aged 35–54 years. Tea consumption was measured using the Block-98 FFQ. Urinary 8-iso-PGF_2α (F₂-IsoP) and 2,3-dinor-5,6-dihydro-15-F_2t-isoprostane (15-F_2t-IsoP-M) were used as biomarkers of oxidative stress. These compounds were measured by MS and normalised to creatinine. Linear regression was used to calculate the geometric mean differences (GMD) and 95% CI for log-transformed urinary F₂-IsoP or 15-F_2t-IsoP-M in relation to black or green tea consumption. We further examined whether adjusting for caffeine impacted associations between tea and oxidative stress. Geometric means of urinary F₂-IsoP and 15-F_2t-IsoP-M were 1·44 (95% CI 1·39, 1·49) and 0·71 (95% CI 0·69, 0·73) ng/mg creatinine, respectively. Overall, green tea consumption was not associated with urinary F₂-IsoP or 15-F_2t-IsoP-M. High-level black tea consumption (≥5 cups/week compared with 0) was associated with higher 15-F_2t-IsoP-M concentrations (adjusted GMD=0·10, 95 % CI 0·02–0.19) but not F₂-IsoP. Adjusting for caffeine nullified the association between black tea and 15-F_2t-IsoP-M. Our findings do not support the hypothesis that dietary tea consumption is inversely associated with oxidative stress.