Lung cancer is the most common cause of cancer death worldwide and in the United States (1). Estimates are that approximately 160,000 Americans will die of lung cancer in 2012.
While genetic susceptibility plays a role in lung cancer risk, cigarette smoking is by far the most important risk factor. Smokers are as much as 23 times more likely to develop lung cancer than non-smokers. Cigar and pipe smoking also increase risk. Other risks include exposure to radon gas released from soil and building materials, and occupational or environmental exposure to secondhand smoke, asbestos (particularly among smokers), certain metals (chromium, cadmium, arsenic), some organic chemicals, radiation, air pollution, and paint (occupational).
Not all lung cancer is a result of smoking, however. Among non-smokers, women are more likely to develop this type of cancer than men (2). It’s possible that the hormone estrogen has something to do with this. Almost twenty years ago, research found that women who had an earlier menopause were less likely to get lung cancer, while those who used hormone therapy were more likely to develop it (3). More recently, in the Women’s Health Initiative trial, use of hormone therapy—estrogen plus progestin—significantly increased the risk of developing aggressive lung cancer (4). In contrast, in a large breast cancer follow-up study, use of the anti-estrogen drug tamoxifen was linked to a reduction in lung cancer deaths (5).
Given that they are uniquely rich sources of phytoestrogens, it is not surprising that there is been considerable interest in the relationship between soyfoods and lung cancer risk. The largest study to examine this issue was conducted in China and just published in the American Journal of Clinical Nutrition. The authors of this study also analyzed other research on this topic. The results of this analysis and the new study show that soyfoods consumption appears to be remarkably protective against lung cancer.
For the new study, investigators enrolled 71,550 postmenopausal women from Shanghai into the study between 1997 and 2000 (6). Women filled out a dietary questionnaire that was designed to comprehensively evaluate soy intake. The subjects were divided into five groups according to the amount of soy they consumed. Over the 9.1 years of follow-up, 370 of the women developed lung cancer. The results show that women in the highest intake group—who consumed an average of about two servings of soyfoods per day—were 37% less likely to develop lung cancer than women who consumed little soy. However, the benefits were limited to non-smokers and were most apparent in women who experienced later menopause. This suggests that soy may be protective by exerting an anti-estrogenic effect. These effects would be most apparent in women who are exposed to estrogen for a longer time, due to their later age of menopause.
The analysis of 7 previous studies produced results very similar to the study from Shanghai. High soy intake was associated with about a 40% reduction in risk for lung cancer. But again, protection was limited to non-smokers. The authors concluded that there is strong evidence that soy is protective against lung cancer in people who don’t smoke. The researchers suggested that soyfoods could have an important public health benefit since lung cancer is increasing among women in many parts of the world. Consuming soyfoods is one easy way to lower risk.
1. Ferlay J, Shin HR, Bray F, et al. Estimates of worldwide burden of cancer in 2008: GLOBOCAN 2008. Int J Cancer 127:2893-917, 2010.
2. Wakelee HA, Chang ET, Gomez SL, et al. Lung cancer incidence in never smokers. J Clin Oncol 25:472-8, 2007.
3. Taioli E, Wynder EL. Re: Endocrine factors and adenocarcinoma of the lung in women. J Natl Cancer Inst 86:869-70, 1994.
4. Chlebowski RT, Schwartz AG, Wakelee H, et al. Oestrogen plus progestin and lung cancer in postmenopausal women (Women’s Health Initiative trial): a post-hoc analysis of a randomised controlled trial. Lancet 374:1243-51, 2009.
5. Bouchardy C, Benhamou S, Schaffar R, et al. Lung cancer mortality risk among breast cancer patients treated with anti-estrogens. Cancer 117:1288-95, 2011.
6. Yang G, Shu XO, Chow WH, et al. Soy food intake and risk of lung cancer: Evidence from the Shanghai Women’s Health Study and a meta-analysis. Am J Epidemiol, 2012.