By Joene Hendry

NEW YORK (Reuters Health) - Men who don't smoke and eat a lot of soy may have a lower risk of lung cancer, according to a new study.

Soy contains isoflavones, which act similarly to the hormone estrogen, and may have anti-cancer qualities in hormone-related cancers of the breast and prostate, the researchers note in the American Journal of Clinical Nutrition. Cells in the lung have properties that suggest they may also respond to isoflavones.

Dr. Taichi Shimazu, of the National Cancer Center in Tokyo, and colleagues studied more than 36,000 Japanese men and more than 40,000 Japanese women, 45 to 74 years old and free of cancer at the start of the study.

The researchers followed the women for about 11 years, after surveying their food intake, smoking status, medical history, and other lifestyle factors between 1995 and 1999.

Overall rates of lung cancer were small: 481 men -- or about one in 75 -- and 178 women, or about one in 225 -- were diagnosed during the 11 years of the study.

Among the slightly more than 13,000 men who never smoked, there were 22 lung cancer cases among men who ate the least soy, and just 13 lung cancer cases among those who ate the most. Shimazu said men's soy intake from food varied widely, from about 34 to about 162 grams per day.

After taking a number of factors into account, the risk about halved in the highest versus the lowest intake group.

There were even fewer lung cancer cases among women, so researchers could draw no conclusions about their risks.

The authors note that men it may not be the act of eating soy that lowered lung cancer risk in the men in their study. Men who eat soy may be more likely to take part in other activities that may lower the risk, or may be more likely to eat other healthy foods. But they did take many of those factors into account.

However, the current study did not gather data on isoflavone supplement use, nor did it look at exposure second-hand smoking. That means these findings should be confirmed among Japanese and other populations, the authors conclude.

In other words, the study does not provide enough evidence to suggest a change in eating behavior, Shimazu told Reuters Health by email.

SOURCE: American Journal of Clinical Nutrition, published online January 13, 2010.