Estrogen-like compounds that come with a soy-rich diet are sometimes linked to a reduced risk of cancer, but new research from Japan suggests that protection doesn't extend to stomach cancer.
In a study that tried to tease apart the effects of isoflavones—also known as phytoestrogens—found in soy, and other nutrients, like salt, Japanese researchers found no difference in gastric cancer risk between people who consumed a lot of isoflavones and those who consumed the least.
Azusa Hara and her colleagues from the National Cancer Center in Tokyo examined data on about 85,000 people in an existing Japanese study.
The researchers estimated how much isoflavone the study's participants ate from a list of questions they had answered in the 1990s, then followed the subjects until the end of 2006 to see how many developed stomach cancer.
During the follow-up period, approximately 1,250 of the study's participants got stomach cancer, but the researchers saw no difference in risk between those who ate the most isoflavone and those who ate the least.
According to Dr. Richard Peek, director of Gastroenterology, Hepatology and Nutrition at Vanderbilt University Medical Center in Nashville, Tennessee, estrogen is thought to protect against stomach cancer because the disease is much more common in men, at least until women are post-menopausal—hinting that younger women's higher estrogen levels might be protecting them.
Peek told Reuters Health there are also studies on mice that suggest estrogen protects against stomach cancer.
The Japanese team, however, found an increase in stomach cancer risk among women taking hormone therapy who ate the most isoflavone-laden food, compared to those who ate the least.
The women in the study on hormone therapy were more likely to smoke, drink and have a family history of stomach cancer, the researchers note, which could explain the link.
Hara and her colleagues wrote in the American Journal of Clinical Nutrition that their results are limited by the use of their questionnaire and the fact that they could not account for whether the subjects were also infected with the bacterium Helicobacter pylori, which is also linked to increased stomach cancer risk.
Still another well-known risk factor for gastric cancers is high salt intake.
According to the American Cancer Society, a person in the United States has a one in 114 chance of developing stomach cancer. An estimated 21,500 Americans were diagnosed with it in 2011 and an estimated 10,500 died from it.
Stomach cancers were once the leading cause of cancer deaths in the U.S. until 1930.
"One of the reasons for decline is that people have fridges now, and they use less salt preservatives," said Khaldoun Almhanna, a medical oncologist at the Moffitt Cancer Center in Tampa, Florida.