Equol producer status, salivary estradiol profile and urinary excretion of isoflavones in Irish Caucasian women, following ingestion of soymilk

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.