Equol production, isoflavone excretion, and the salivary estradiol profile among 36 females, native Irish Caucasian volunteers following ingestion of 200 mL soymilk is reported. The soymilk contained daidzein (73 ± 6.7 mg) and genistein (86 ± 10.2 mg). Volunteers provided personal and family medical history. Dietary analysis revealed that all volunteers regularly consumed soy-based or soy-supplemented food products. The mean age, mean age at menarche, and body mass index of volunteers were 46.6 ± 12.3 years, 13.1 years and 26.1, respectively. The average number of children per volunteer was 2.13. Twelve (34%) of the volunteers were found to be first-degree relatives of breast cancer patients. Following consumption of the soymilk, equol was detected in the urine of 18 (51%) of the volunteers. Mean urinary daidzein and genistein concentrations during the hours following soymilk ingestion were 13.5 and 16.7 μg/mg creatinine, respectively, however, some volunteers excreted little (less than 4.0 μg/mg) or no isoflavone. Salivary estradiol in most (24) volunteers had decreased from 51.5 ± 28.67 pmol/L pre-ingestion to 29.75 ± 16.13 pmol/L 5 h after drinking the soymilk. However, the salivary estradiol in 12 subjects (34%) increased from 33.76 ± 13.4 pmol/L to 137.4 ± 65.64 pmol/L over the same period. Individuals whose salivary estradiol increased had significantly less children (1.58 ( P < 0.05)), were more likely to (a) return urine samples with low isoflavone content (50.3% compared to 25%), (b) to be equol producers (67% compared to 41.7%), and (c) to be first-degree relatives of breast cancer patients (41.7% compared to 25%). Volunteers who reported a first-degree link to breast cancer were more likely to have a higher body mass index (29.0 compared to 26.1 ( P < 0.05)), to be equol producers (75% compared to 51%), and to excrete isoflavones in low quantities only (60% compared to 50%). First-degree relatives also had fewer children (1.75 ( P < 0.05)). The results indicate a significant, distinctive variation in equol production, isoflavone excretion and salivary estradiol profile among individual volunteers following ingestion of soymilk.
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