Soy food and isoflavone intake and colorectal cancer risk: The Fukuoka Colorectal Cancer Study

Abstract

Objective. It has been suggested that soy food and isoflavone intake may be protective against the risk of colorectal cancer. However, epidemiologic evidence remains sparse and inconsistent. We addressed this issue in the Fukuoka Colorectal Cancer Study. Material and methods. The study subjects were the 816 incident cases of histologically confirmed colorectal cancer and 815 community controls. Intakes of soy foods and isoflavones were assessed by in-person interview using a computer-assisted dietary method. Logistic regression analysis was applied to estimate odds ratio (OR) and 95% confidence interval (CI) of colorectal cancer with adjustment for dietary intakes of calcium and n-3 polyunsaturated fatty acids as well as for body mass index, physical activity, alcohol use, and other lifestyle factors. Results. Energy-adjusted intakes of soy foods (dry weight) and isoflavones were inversely associated with colorectal cancer risk in men and postmenopausal women, but not in premenopausal women. The multivariate-adjusted OR for the highest versus lowest quintile was 0.65 (95% CI 0.41–1.03, p for trend = 0.03) for soy foods and 0.68 (95% CI 0.42–1.10, p for trend = 0.051) for isoflavones in men. The corresponding values for postmenopausal women were 0.60 (95% CI 0.29–1.25, p for trend = 0.053) and 0.68 (95% CI 0.33–1.40, p for trend = 0.049). The site-specific analysis showed inverse associations of soy foods (p for trend = 0.007) and isoflavones (p for trend = 0.02) with rectal cancer in men. Conclusion. The findings add to epidemiologic evidence for protective effects of soy foods and isoflavones in colorectal carcinogenesis.

Key Words::

• Colorectal cancer
• isoflavones
• soy foods

Acknowledgments

This study was supported by a Grant-in-Aid for Cancer Research on Priority Areas (20014018) form the Ministry of Education, Culture, Sports, Science and Technology, Japan. The authors acknowledge support from Emeritus Professors Keizo Sugimachi, Seiyo Ikeda, Sumitaka Arima, and Takayuki Shirakusa and from Drs. Motonori Saku, Yoichi Ikeda, Soichiro Maekawa, Kazuo Tanoue, Kinjiro Sumiyoshi, and Shoichiro Saito in conducting the survey of cases. The following physicians kindly supervised the survey of controls at their clinics: Drs. Hideaki Baba, Tomonori Endo, Hiroshi Hara, Yoichiro Hirokata, Motohisa Ikeda, Masayoshi Ishibashi, Fumiaki Itoh, Yasuhiro Iwanaga, Hideki Kaku, Shoshi Kaku, Minoru Kanazawa, Akira Kobayashi, Ryunosuke Kumashiro, Shinichi Matsumoto, Soukei Mioka, Umeji Miyakoda, Osamu Nakagaki, Nobuyoshi Nogawa (deceased), Nobuyuki Ogami, Toyoaki Okabayashi, Hironao Okabe, Nishiki Saku, Masafumi Tanaka, Masahiro Ueda, Bunichi Ushio, and Koheisho Yasunaga.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.