Determination of the isoflavonoids genistein and daidzein in biological samples by gas chromatography-mass spectrometry.

Background: The marked differences in the incidences of both breast and prostate cancer between the East and the West have been attributed to habitual diet. Traditionally, Japanese and Far Eastern people in general consume large quantities of soya and soya-derived foodstuffs. Diphenolic soya phytoestrogens have weak oestrogenic and anti-oestrogenic properties and have been implicated in preventing or limiting the early processes associated with breast and prostate carcinogenesis.

Methods: We have developed a gas chromatography-mass spectrometry procedure that is suitable for measurement of the phytoestrogens daidzein and genistein in serum, urine and tissue samples.

Results: In serum samples of Japanese subjects mean (standard deviation) concentrations of daidzein [men, 281 (375.5) nmol/L; women, 246 (369.4) nmol/L] and genistein (men, 493 (604.4) nmol/L; women, 502 (717.6) nmol/L] were approximately 15 times higher than the mean levels achieved in British men [daidzein, 18.2 (20.4) nmol/L; genistein, 34.1 (27.2) nmol/L] and women [daidzein, 13.5 (11.6) nmol/L; genistein, 30.1 (31.2) nmol/L]. In pharmacokinetic studies of British subjects, maximum levels of daidzein and genistein were achieved within 6-8 h after the consumption of a cereal bar containing 20 mg of soya isoflavonoids; these levels were very similar to the mean levels achieved in normal Japanese subjects. Unlike serum, the mean daidzein concentration in urine from British subjects was higher than the mean genistein concentration (1.66 and 0.72 micromol per 24 h, respectively); following soy supplementation, urinary isoflavonoid levels were increased at least 10-fold.

Conclusions: Serum daidzein and genistein concentrations are lower in British subjects than in Japanese subjects; this may be due to dietary differences.