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 μmol
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.
