ABSTRACT
BACKGROUND & OBJECTIVE: Soy isoflavones are being used as therapy for menopausal syndrome in many countries. Marketed preparations show variability in bioavailability and there are variations in kinetics due to ethnicity and diet. Inspite of soy isoflavone being available in the Indian market there are no studies to show whether the preparation is likely to be effective in women. This study was carried out to determine circulating levels of genistein, a bioactive soy isoflavone, in Indian women after a single dose of soy extract. METHODS: Six healthy vegetarian women volunteers, between 36 and 62 yr and with a mean body mass index (BMI) 25.01+/-2.02 (kg/m2), were enrolled after an informed consent. Women with antibiotic or Soy food intake within 1 month of study were excluded. A single dose of standardized soy extract capsule containing 64.12 mg of total isoflavones (genistein content equivalent to 31.76 mg) was ingested under supervised fasting condition and multiple blood samples were collected at 0, 1, 2, 4, 6, 8 and 24 h. Genistein levels were measured by high performance liquid chromatography (HPLC) method with a detection level of 2.5 ng/100 microl of injection volume. The intra- and inter-assay coefficients of variation were < 5.32 per cent. RESULTS: Genistein was detected (10.3 to 16.2 ng/ml) in 3 volunteers in baseline samples. Within one hour genistein levels rose from 42 ng to 215 ng/ml with a maximum concentration of 117 to 380 ng/ml at 4 to 8 h. A secondary peak suggestive of enterohepatic circulation was seen between 4 and 6 h in 2 out of 6 volunteers. The mean Cmax was 315.5 +/- 57.1 ng/ml. All women had detectable levels from 25.2 to 109.3 ng/ml at 24 h. INTERPRETATION & CONCLUSION: Our study showed adequate circulating levels of genistein in Indian vegetarian women after a single dose of soy extract. Variability in plasma levels of the soy isoflavones may explain differences in responses to therapy.