Determination of phytoestrogens in dietary supplements by LC-MS/MS
Résumé
Labeling data quantifying the exact content of individual phytoestrogen analytes in dietary supplements is generally poor. As these products are commonly used in the management of menopause symptoms, any clinical benefits would be dependent on the exact dosage of isoflavones received. Well established extraction procedures and updated Isotope Dilution Mass Spectrometry LC-MS/MS have been used to accurately quantify the concentrations of 10 common isoflavones in 35 dietary supplement samples on sale in the UK, Canada and Italy. Concentration specific ionization suppression is described for biochanin A and formononetin. All supplements contained phytoestrogens. The soya isoflavones (genistein, daidzein, glycitein) were present in all products and the majority also contained the red clover isoflavones (biochanin A, formononetin) and some the Kudzu isoflavones (daidzein, puerarin). The content of total isoflavones per dose ranged from <1 to 53 mg. Trace amounts of coumestrol were found in 6 products. Other less common analytes, the prenylnaringenins (6-prenylnaringenin, 8-prenylnarigenin, 6,8-diprenylnaringenin) were not found in any of the products. Only 14 of 35 supplements were found to deliver more than or equal to 40 mg/day of aglycone isoflavones, a consensus dose value recognized as delivering therapeutic benefit. 11 did not match label claims. Six delivered less than 10 mg/day isoflavones. There has been little improvement in the overall quality of industry labeling in the five years since this was last investigated. Consequently, the public, retailers and health care professionals should consider using standardised isoflavone supplements, which are supported by analytical measurements.
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