There are a number of studies available on the potential beneficial effect of soya and breast and prostate cancer. But there is also the potential for soya to reduce the risk of other cancers. Animal data shows that soya can inhibit the growth of bladder tumors and can reduce pulmonary metastases (1,2).
The soyabean saponins and phytosterols seems to act as chemoprotective agents for colon cancer (3,4). A meta-analysis of epidemiologic studies found that the non-fermented soyafood intake was associated with a reduced risk of stomach cancer (5). The study concluded that because of the potential confounders the role of soya in the etiology of stomach cancer could not be determined with confidence.
Endometrial cancer
Incidence rates of endometrial cancer vary more than 10-fold worldwide with Asian countries having a low incidence of endometrial cancer. An inverse association between phytoestrogen consumption and risk of endometrial cancer was found in a multiethnic population among Western women (6). This case-control study of 500 African, American, Latina, and white women with endometrial cancer and 470 age- and ethnicity-matched control women was conducted in the San Francisco Bay Area. Odds ratio’s were calculated for the highest versus lowest quartile of exposure. Isoflavone (OR = 0.59) and lignan (OR = 0.68) consumptions were inversely related to the risk of endometrial cancer. These associations were slightly stronger in postmenopausal women (OR = 0.44 and OR = 0.57). Obese postmenopausal women consuming relatively low amounts of phytoestrogens had the highest risk of endometrial cancer (OR = 6.9 compared with non-obese postmenopausal women consuming relatively high amounts of isoflavones). Thus some phytoestrogenic compounds, at the levels consumed in the typical American-style diet, are associated with reduced risk of endometrial cancer Similarly, a study in a Chinese population found that regular consumption of soyfoods was inversely associated with the risk of endometrial cancer. Compared with women with the lowest quarter of intake, the adjusted odds ratio of endometrial cancer was reduced from 0.93 to 0.85 and 0.67 with increasing quarter of soy protein intake. A similar inverse association was observed for soy isoflavone intake. The inverse association seemed to be more pronounced among women with high BMI and waist to hip ratio. Median soy protein intake was 9.9 g/d in the cases and 10.2 g/d in the controls; median isoflavone intake was 40.5 mg/d in cases and 42.5 mg in controls. The authors concluded that regular intake of soyfoods is associated with a reduced risk of endometrial cancer (7).
Colorectal cancer
The potential relation between flavonoids and colorectal cancer risk was investigated using data from a multicentric Italian case-control study, including 1,953 cases of colorectal cancers (1,225 colon cancers and 728 rectal cancers) and 4,154 controls (8). A reduced risk of colorectal cancer was found for increasing intake of isoflavones (OR=0.76, for the highest versus the lowest quintile). The estimates did not substantially differ for colon and rectal cancers, as well as in strata of sex, age, and body mass index. The findings of this large study provide support for an inverse association of selected classes of flavonoids with colorectal cancer risk. A case-control study in Canada evaluated the association between phytoestrogen intake and colorectal cancer risk (9): 1095 Colorectal cancer cases were sex and age matched with 1890 control subjects. Dietary lignan intake was associated with a significant reduction in colorectal cancer risk (OR of 0.73 for highest versus lowest tertile) as was isoflavone intake (OR = 0.71). This finding that phytoestrogen intake may reduce colorectal cancer risk is important, because dietary intake is potentially modifiable.
Lung cancer
A research group in Texas evaluated the relationship between dietary intake of phytoestrogens and risk of lung cancer in a case-control study of 1,674 patients with lung cancer and 1,735 matched healthy controls (10). Reductions in risk of lung cancer tended to increase with each increasing quartile of phytoestrogen intake. The highest quartile of total phytoestrogens from food sources only (OR= 0.54; P<.001 for trend) were associated with 46% reductions in risk of lung cancer compared to the lowest quartile of intake. Sex-specific effects were also apparent. For men, statistically significant trends for decreasing risk with increasing intake were noted for each phytoestrogen group (isoflavones and lignans): protective effects for the highest quartile of intake ranging from 27% for lignans to 44% for isoflavones. While in women, significant trends were only present for intake of total phytoestrogens from food sources only, with a 34% protective effect for the highest quartile of intake.
References :
- Zhou JR, Mukherjee P, Gugger ET, Tanaka T, Blackburn GL, Clinton SK. Inhibition of murine bladder tumorigenesis by soy isoflavones via alterations in the cell cycle, apoptosis, and angiogenesis. Cancer Res 1998;58(22):5231-8.
- Li D, Graef GL, Yee JA, Yan L. Dietary supplementation with high-selenium soy protein reduces pulmonary metastasis of melanoma cells in mice. J Nutr 2004;134(6):1536-40.<
- Koratkar R, Rao AV. Effect of soya bean saponins on azoxymethane-induced preneoplastic lesions in the colon of mice. Nutr Cancer 1997;27(2):206-9.
- Rao AV, Janezic SA. The role of dietary phytosterols in colon carcinogenesis. Nutr Cancer 1992;18(1):43-52.
- Wu AH, Yang D, Pike MC. A meta-analysis of soyfoods and risk of stomach cancer: the problem of potential confounders. Cancer Epidemiol Biomarkers Prev 2000;9(10):1051-8
- Horn-Ross PL, John EM, Canchola AJ, Stewart SL, Lee MM. Phytoestrogen intake and endometrial cancer risk. J Natl Cancer Inst 2003;95:1158-64.
- Xu WH, Zheng W, Xiang YB et al. Soya food intake and risk of endometrial cancer among Chinese women in Shanghai: population based case-control study. BMJ 2004;328:1285.
- Rossi M, Negri E, Talamini R et al. Flavonoids and colorectal cancer in Italy. Cancer Epidemiol Biomarkers Prev 2006;15:1555-8.
- Cotterchio M, Boucher BA, Manno M, Gallinger S, Okey A, Harper P. Dietary phytoestrogen intake is associated with reduced colorectal cancer risk. J Nutr 2006;136:3046-53.
- Schabath MB, Hernandez LM, Wu X, Pillow PC, Spitz MR. Dietary phytoestrogens and lung cancer risk. JAMA 2005;294:1493-504