Posted online March 25, 2013 on www.jco.org .
Analysis of data collected in a large, population-based study in Shanghai, China, showed women who consumed higher amounts of soy food in the years leading up to their diagnosis of lung cancer lived longer. These results offer the first scientific evidence that consuming soy food before cancer diagnosis may be associated with significantly improved survival in patients with lung cancer.
A comprehensive food-frequency questionnaire was used to assess usual dietary intake of soy foods commonly consumed in Shanghai, such as tofu, soy beans, soy milk, and soy sprouts. Information on usual dietary intake was collected at study enrollment and updated 2-3 years later.
The researchers identified 444 cases of lung cancer among the 74,941 study participants. At 12 months after diagnosis, nearly 60 percent of the patients who ate the most soy and 50 percent of those who ate the least soy were alive.
During a median follow-up period of 36 months, the risk of dying from any cause decreased with increasing soy food intake, until the intake reached the equivalent of approximately 4 ounces of tofu per day; adding more soy to the diet did not appear to provide additional survival benefit for lung cancer patients. The benefits were highest for women who never smoked.
What This Means for Patients
The findings add to growing evidence suggesting that estrogen plays a role in lung cancer development and growth and that soy, which contains estrogen-like substances called isoflavones, may favorably affect lung cancer survival. A recent study by the same research team reported that high intake of soy food was associated with a 40 percent decrease in lung cancer risk.
While these early results are very promising, it would be premature to make any dietary recommendations based on this single study. The study was conducted in a population of women with very low prevalence of cigarette smoking, a known risk factor for lung cancer development and postmenopausal hormone therapy use –a factor that may negatively influence lung cancer prognosis. More research is needed to see if similar benefits would be seen in other populations, such as women who smoke and those who have undergone hormone replacement therapy.
Usual soy food intake among Shanghai women is higher than among non-Asian women. But given the increasing popularity of soy food in the Western world, this research may have broader relevance.