Spanish and British scientists have discovered how green tea helps to prevent certain types of cancer.

Researchers at the University of Murcia in Spain (UMU) and the John Innes Center (JIC) in Norwich, England have shown that a compound called EGCG in green tea prevents cancer cells from growing by binding to a specific enzyme.

"We have shown for the first time that EGCG, which is present in green tea at relatively high concentrations, inhibits the enzyme dihydrofolate reductase (DHFR), which is a recognized, established target for anti-cancer drugs, " Professor Roger Thorneley, of JIC, stated.

"This is the first time, to our knowledge, a known target for an anti-cancer drug has been identified as being inhibited by EGCG," he added.

Green tea has about five times as much EGCG as regular tea, studies have shown. It decreased rates of certain cancers but scientists were not sure what compounds were involved or how they worked. Nor had they determined how much green tea a person would have to drink to have a beneficial effect, he said.

Thorneley said EGCG is probably just one of a number of anti-cancer mechanisms in green tea.

"We have identified this enzyme in tumour cells that EGCG targets and understand how it stops this enzyme from making DNA. This means we may be able to develop new anti-cancer drugs based on the structure of the EGCG molecule," Thorneley explained.

The scientists decided to look at ECGC after they realized its structure was similar to a cancer drug called methotrexate.

"We discovered that EGCG can kill cancer cells in the same way as methotrexate," Dr Jose Neptuno Rodriguez-Lopez, of UMU, a joint author of the research published in the journal Cancer Research.

EGCG binds strongly to DHFR, which is essential in both healthy and cancerous cells. But it does not bind as tightly as methotrexate, so its side effects on healthy cells could be less severe than those of the drug.

Thorneley said EGCG could be a lead compound for new anti-cancer drugs.

The findings could also explain why women who drink large amounts of green tea around the time they conceive and early in their pregnancy may have an increased risk of having a child with spina bifida or other neural tube disorders.

Women are advised to take supplements of folic acid because it protects against spina bifida. But large amounts of green tea could decrease the effectiveness of folic acid.

"This enzyme, (DHFR), is the one folic acid supplements are given for. Folic acid deficiency leads to neural tube development defects," Thorneley added.