CASE-CONTROL STUDY OF PHYTO-ESTROGENS AND BREAST-CANCER

Background Phyto-oestrogens are a group of naturally occurring chemica ls derived from plants; they have a structure similar to oestrogen, an d form part of our diet. They also have potentially anticarcinogenic b iological activity. We did a case-control study to assess the associat ion between phyto-oestrogen intake (as measured by urinary excretion) and the risk of breast cancer. Methods Women with newly diagnosed earl y breast cancer were interviewed by means of questionnaires, and a 72 h urine collection and blood sample were taken before any treatment st arted. Controls were randomly selected from the electoral roll after m atching for age and area of residence. 144 pairs were included for ana lysis. The urine samples were assayed for the isoflavonic phyto-oestro gens daidzein, genistein, and equol, and the lignans enterodiol, enter olactone, and matairesinol. Findings After adjustment for age at menar che, parity, alcohol intake, and total fat intake, high excretion of b oth equol and enterolactone was associated with a substantial reductio n in breast-cancer risk, with significant trends through the quartiles : equol odds ratios were 1.00, 0.45 (95% CI 0.20, 1.02), 0.52 (0.23, 1 .17), and 0.27 (0.10, 0.69)-trend p=0.009-and enterolactone odds ratio s were 1.00, 0.91 (0.41, 1.98), 0.65 (0.29, 1.44), 0.36 (0.15, 0.86)-t rend p=0.013 For most other phytoestrogens there was a reduction in ri sk, but it did nat reach significance. Difficulties with the genistein assay precluded analysis of that substance. Interpretation There is a substantial reduction in breast-cancer risk among women with a high i ntake (as measured by excretion) of phyto-oestrogens-particularly the isoflavonic phyto-oestrogen equol and the lignan enterolactone. These findings could be important in the prevention of breast cancer.