They studied the lifestyles and tea drinking habits of 1,370 middle-aged men living in Yoshimi, near Tokyo, and analysed their blood. The findings are based on men who drank up to three cups a day, four to 9 cups a day or more than 10 cups a day.
Dr Kazue Imai, epidemiologist at the Saitama Cancer Centre Research Institute, Saitama district, says in the British Medical Journal that they found high consumption - especially more than 10 cups a day - reduced potentially harmful blood fat levels.
They also believe that high levels of green tea drinking may protect liver cells which, by reducing the output of harmful blood chemicals, may lower the risk of cancer. They have started more trials in this area.
Some studies of black tea have been carried out but results were flawed because they did not include heavy tea drinkers, Dr Imai says.
In a separate article in the Lancet, results of an international study found that the drug captropil could save thousands of lives if used routinely after a heart attack.
The drug, one of a group known as Ace inhibitors, was designed to treat high blood pressure and the chronic condition of heart failure.
The study among 58,000 acute heart attack patients found that the drug saved one in 200 patients treated. It was used in combination with aspirin and a clot-busting drug.
Dr Rory Collins, the British Heart Foundation senior research fellow and co-ordinator of the research said: "In British coronary care units alone appropriate widespread use of Ace inhibitors would save a few hundred lives a year."