Abstract
BackgroundIsoflavones from soybeans may provide some beneficial impacts on postmenopausal health. The purpose of this study was to compare the pharmacokinetics and bioavailability of plasma isoflavones (daidzein and genistein) after a single dose of orally administered soy beverage and soy extract capsules in postmenopausal Thai women.MethodsWe conducted a randomized two-phase crossover pharmacokinetic study in 12 postmenopausal Thai women. In the first phase, each subject randomly received either 2 soy extract capsules (containing daidzin : genistin = 7.79 : 22.57 mg), or soy beverage prepared from 15 g of soy flour (containing daidzin : genistin = 9.27 : 10.51 mg). In the second phase, the subjects received an alternative preparation in the same manner after a washout period of at least 1 week. Blood samples were collected immediately before and at 0.5, 1, 2, 4, 6, 8, 10, 12, 24 and 32 h after administration of the soy preparation in each phase. Plasma daidzein and genistein concentrations were determined by using high performance liquid chromatography (HPLC). The pharmacokinetic parameters of daidzein and genistein, i.e. maximal plasma concentration (Cmax), time to maximal plasma concentration (Tmax), area under the plasma concentration-time curve (AUC) and half-life (t1/2), were estimated using the TopFit version 2.0 software with noncompartmental model analysis.ResultsThere were no significant differences in the mean values of Cmax/dose, AUC0–32/dose, AUC0-∝/dose, Tmax, and t1/2 of genistein between both preparations. For pharmacokinetic parameters of daidzein, the mean values of Cmax/dose, Tmax, and t1/2 did not significantly differ between both preparations. Nonetheless, the mean AUC0–32/dose and AUC0-∝/dose after administration of soy extract capsules were slightly (but significantly, p < 0.05) higher than those of soy beverage.ConclusionThe bioavailability of daidzein, which was adjusted for the administered dose (AUC/dose), following a single oral administration of soy beverage was slightly (but significantly) less than that of soy extract capsules, whereas, the bioavailability adjusted for administered dose of genistein from both soy preparations were comparable. The other pharmacokinetic parameters of daidzein and genistein, including Cmax adjusted for the dose, Tmax and t1/2, were not different between both soy preparations.
Highlights
Isoflavones from soybeans may provide some beneficial impacts on postmenopausal health
Isoflavone contents in soy preparations The quantification of isoflavone contents demonstrated that both soy flour and soy extract capsule preparations contained predominantly daidzin and genistin, whereas, aglycones were rarely found and isoflavones in other forms were not measured
Pharmacokinetics of daidzein and genistein in healthy postmenopausal Thai women The Mean plasma daidzein and genistein concentrationtime curves after a single dose of both orally administered soy preparations are shown in Figure 2, 3
Summary
Isoflavones from soybeans may provide some beneficial impacts on postmenopausal health. Estrogen replacement therapy after menopause improves the health and quality of life for women. The Women's Health Initiative (WHI) randomized controlled trial has recently found that estrogen-alone hormone therapy reduces the risk of hip and other fractures in healthy postmenopausal women with prior hysterectomy, it significantly increases the risk of stroke (but has no significant effect on the risk of coronary heart disease, breast or colorectal cancer) [2]. Long-term estrogen replacement therapy in postmenopausal women who have a uterus might has the disadvantage of being tissue agonists for endometrial tissue, which increases the incidence of endometrial cancer [3]. Adding progestin to estrogen can be used to prevent the development of endometrial cancer, this combination may cause some unwanted side effects, i.e. breast cancer, venous thromboembolism, stroke and coronary heart disease [3]. Alternative therapies, which include natural products such as phytoestrogens and herbs, offer attractive options because they may protect against breast and endometrial cancer, have fewer side effects and still provide health benefits [4]
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