Drinking green tea doesn't dilute breast cancer risk

BMJ Group News

Drinking green tea doesn't protect against breast cancer, reports a new study from Japan. The researchers found that women who drank several cups a day were just as likely to develop breast cancer as those who drank less than one cup a week.

What do we know already?

Green tea is often touted for its health benefits. It's a rich source of polyphenol antioxidants, which studies suggest may reduce the risk of cardiovascular disease and cancer.

There's been particularly strong interest in green tea's possible effect on breast cancer, as the tea is consumed widely in Japan and other Asian countries where breast cancer is less common. Animal and laboratory studies have suggested that green tea may inhibit the growth of breast cancer cells. But the studies done in humans have had conflicting results.

Researchers looked at data on nearly 54,000 middle-aged women in Japan. Over five years, the participants completed two detailed questionnaires asking about their health, lifestyle, and diet, including their consumption of green tea. The researchers then tracked who developed breast cancer using a government-run cancer registry to confirm each diagnosis. On average, the study followed the women for 13.6 years.

What does the new study say?

The researchers found no difference in breast cancer risk based on how much green tea the women drank. Those who drank five or more cups a day were no less likely to develop breast cancer than those who drank less than one cup per week.

The researchers also found no difference in risk when looking at two specific types of green tea (sencha and bancha/genmaicha). And there was no variation when they focused on subtypes of breast cancer (whether the cancer was sensitive to the hormones oestrogen or progesterone) and whether the women had gone through the menopause.

The findings also take into account several other factors that can influence breast cancer risk, including age at first period, age at the menopause, use of hormone replacement therapy (HRT), body mass index (BMI), physical activity, and alcohol intake.

How reliable are the findings?

This was a well-designed study and its findings are compelling, particularly since green tea's purported effect on breast cancer is partly based on the lower risk of this disease among Japanese women. This study strongly suggests that their reduced risk is not related to their intake of green tea.

However, this type of study can't prove conclusively that green tea has no effect on breast cancer risk. And since the study only included Japanese women, we can't be certain that these findings apply to other groups. For example, it's possible that green tea might have a different effect in women of other ethnic backgrounds, or with different diets.

Where does the study come from?

The study was conducted by researchers in Japan and the US, and it was funded by research grants from the Japanese government. It was published in Breast Cancer Research, which is owned by BioMed Central.

What does this mean for me?

If you drink green tea, you should do so primarily because you enjoy it, not because you expect it to lower your risk of breast cancer or another disease. As this study shows, the health benefits attributed to green tea are still not certain.

What should I do now?

If you are concerned about getting breast cancer, talk to your doctor about how you might lower your risk. Studies show that exercising regularly, eating a diet that is low in fat, and not drinking much alcohol can make a difference.