According to a study, long-term consumption of high-dose green tea extract may offer some protection against cancer, cardiovascular disease, obesity, and type 2 diabetes, but it may also cause liver damage in a small number of people.
The research team investigated whether people with certain genetic variations were more likely than others to show signs of liver stress after a year of ingesting 843 milligrams per day of the predominant antioxidant in green tea, a catechin called epigallocatechin gallate (EGCG).
An analysis by researchers showed that early signs of liver damage were somewhat more common than normal in women with one variation in the Catechol-O-methyltransferase (COMT) genotype and strongly predicted by a variation in the uridine 5'-diphospho-glucuronosyltransferase 1A4 (UGT1A4) genotype.
On average, participants with the high-risk UGT1A4 genotype saw the enzyme that indicates liver stress go up nearly 80 percent after nine months of consuming the green tea supplement, while those with low-risk genotypes saw the same enzyme go up 30 percent.