Effect of green tea supplements on liver enzyme elevation: Results from a randomized intervention study in the United States

Liver injury effects of green tea–based products have been reported in sporadic case reports. However, no study has examined systematically such adverse effects in an unbiased manner. We examined the potential effects of a high, sustained oral dose of green tea extract (GTE) on liver injury measures in a randomized, placebo-controlled, double-blinded phase II clinical trial, which enrolled 1,075 women with the original aim to assess the effect of daily GTE consumption for 12 months on biomarkers of breast cancer risk. The current analysis examined the effect of GTE consumption on liver injury in 1,021 participants (513 in GTE and 508 in placebo arm) with normal baseline levels of liver enzymes. Among women in the GTE arm, alanine aminotransferase (ALT) increased by 5.4 U/L [95% confidence interval (CI), 3.6–7.1] and aspartate aminotransferase increased by 3.8 U/L (95% CI, 2.5–5.1), which were significantly higher than those among women in the placebo arm (both P < 0.001). Overall, 26 (5.1%) women in GTE developed moderate or more severe abnormalities in any liver function measure during the intervention period, yielding an OR of 7.0 (95% CI, 2.4–20.3) for developing liver function abnormalities as compared with those in the placebo arm. ALT returned to normal after dechallenge and increased again after one or more rechallenges with GTE. The rise–fall pattern of liver enzyme values following the challenge–dechallenge cycles of GTE consumption strongly implicates the effect of high-dose GTE on liver enzyme elevations.