London, March 15: The reason that green tea can protect against some cancers but also raise the risk of birth defects when drunk by pregnant women is revealed by new research today.
Earlier studies showed that one of the tea's active ingredients is a naturally occurring polyphenol called EGCG. Today's work, published in the journal Cancer Research, shows EGCG could provide the starting point for a new family of anti-cancer drugs.
The team, at John Innes Centre (JIC), Norwich, and the University of Murcia, Spain, found that EGCG disables the enzyme dihydrofolate reductase, DHFR, an established target for anti-cancer drugs which is also implicated in birth defects.
Professor Roger Thorneley, head of the JIC team, said: 'For the first time we have a clear scientific explanation of why EGCG inhibits the growth of cancer cells at concentrations which are found in the blood of people who drink two or three cups of green tea a day.'
The target enzyme, DHFR, is essential for making DNA in both normal and tumour cells. But tumour cells grow and divide more quickly than normal cells and have higher levels of DHFR activity.
Drugs called antifolates already selectively kill cancer cells by putting DHFR out of action.
At the concentrations found in green tea drinkers' blood and other tissues, EGCG kills cancer cells the same way, the team found.
New types of antifolate drugs are being developed because methotrexate, a successful anti-cancer treatment, and related drugs cause side effects by damaging healthy cells, for instance in the liver.
The work also shows why other studies have linked high levels of green tea consumption by women around the time of conception and in pregnancy to an increased incidence of spina bifida and anencephaly. These are neural tube defects linked to folic acid deficiency.
In green tea drinkers, EGCG's antifolate activity would be expected to lessen the activity of the enzyme that uses folic acid, minimising the good effects of folic acid supplements.