Drinking green tea may lower your risk of developing certain blood cancers, but it will take about 5 cups a day, according to a study from Japan.

Drinking green tea has been associated with lower risk of dying and heart disease deaths, Dr. Toru Naganuma, at Tohoku University School of Medicine in Sendai, Japan told Reuters Health in an email correspondence.

The current study, Naganuma said, suggests drinking green tea may have a favorable effect for particular cancers.

After gathering information on the diets and green tea drinking habits of a large group of Japanese adults aged 40 to 79 years old, Naganuma and colleagues followed the group for development of blood and lymph system cancers. The lymph system is a major component of the body's immune system.

The 19,749 men and 22,012 women who participated in the study had no previous history of cancer, Naganuma and colleagues note in the American Journal of Epidemiology.

During 9 years of follow up, 157 blood, bone marrow, and lymph system cancers developed in the study group.

Naganuma's team found that the overall risk for blood cancers was 42 percent lower among study participants who drank 5 or more, versus 1 or fewer, cups of green tea daily.

Drinking 5 or more cups of green tea daily was also associated with 48 percent lower risk for lymph system cancers.

These associations held up in analyses that allowed for age, gender, education, smoking status and history, alcohol use, and fish and soybean consumption.

The researchers also observed reduced risk for blood-related cancers among obese study participants, who are considered to have higher risk of these cancers, Naganuma said.

The investigators say further studies are needed to confirm the health benefits of drinking green tea, and to determine whether daily consumption might prevent certain cancers.

SOURCE: American Journal of Epidemiology, September 15, 2009

Japan Medicine Cancer