A new study of Japanese women showed no evidence for a protective association between soy food or isoflavone intake and risk of endometrial cancer.

Soy foods are an almost exclusive dietary source of isoflavones, a plant-derived estrogen. Some studies have highlighted their potential for cancer protection. However, research looking at the link between consumption of soy food or isoflavones and endometrial cancer has given inconsistent results.

This population-based prospective cohort study of 49,121 Japanese women, age 45 to 74 years examined responses to a food survey questionnaire. The food questionnaire asked about the consumption of eight soy food items such as miso soup, tofu, and soymilk.

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Researchers looked at the total dietary intake of genistein and daidzein, two different types of isoflavones, and divided the women into three groups based on their intake of soy foods and isoflavones.

Women consuming more isoflavones were older, less likely to be current smokers, less likely to consume alcohol and coffee on a regular basis, and more likely to have a history of diabetes. They also had a higher dietary intake of fruit and vegetables.

Higher consumption of total soy foods and isoflavones was not associated with risk of endometrial cancer after adjustment for factors such as age, alcohol consumption, smoking, body mass index, menopausal status, coffee intake, and number of deliveries.

“Our study found that intake of soy and isoflavones was not associated with the risk of endometrial cancer,” said Motoki Iwasaki, MD, PhD, National Cancer Center, Tokyo, Japan. “Although the incidence of endometrial cancer is much lower in Asian countries, the incidence rate has been increasing. We know that the consumption of soy foods among Japanese people is very high. Further studies are needed to verify these findings.”

“This large population-based study found no evidence of a protective association of soy food or isoflavone intake. Confirmation of these results needs further investigation and larger more diverse studies,” said John Thorp, BJOG Deputy-Editor-in-Chief.

This study was published in BJOG: An International Journal of Obstetrics and Gynaecology (2014; doi:10.1111/1471-0528.12853).