Women who eat a lot of soybean products are three to four times more likely to develop liver cancer than those who eat only a small amount, a major government health survey has found.

It is known that isoflavones contained in soybeans lower the risk of breast cancer, but the results highlight the risks of excessive consumption. The Ministry of Health, Labor and Welfare research team that carried out the survey says isoflavones should be consumed in moderation, through people's daily diets.

In its survey, the team followed the health of roughly 20,000 people in six prefectures between 1993 and 2005. The participants were aged between 40 and 69 at the start of the survey. Altogether, 69 men and 32 women developed liver cancer. Participants were asked how much soybean products they ate, and the relationship between two isoflavone constituents and the rate of cancer was examined.

A clear connection between the amount consumed and the risk of liver cancer was seen only in women. Women in the group that consumed the most (80 grams or more of bean curd, or two-thirds or more of a pack of natto per day) were between 3.2 and 3.9 times more likely to develop liver cancer than the group that ate the least (less than 40 grams of bean curd or less than one-third of a pack of natto per day).

Norie Kurahashi, a researcher in the National Cancer Center's Epidemiology and Prevention Division who was part of the ministry's team, said that the structure of isoflavone constituents is similar to the female hormone estrogen. Estrogen heightens the risk of breast cancer, but protects against liver cancer. It is believed that excessive consumption of isoflavones may block this property.

"The greatest risk factors for liver cancer are the type B and C hepatitis viruses. We want women to check whether they are infected, and if they are, we want them to take care not to consume too much soybean products," Kurahashi said. However, the researcher added, "Even if they are not infected, there is a need to take care not to consume too much."

http://mdn.mainichi.jp/mdnnews/news/20090311p2a00m0na001000c.html