To the Editor: Preparations containing isoflavone phytoestrogens are widely used as an alternative therapy for treating symptoms of the menopause. Although Australian government regulations strictly control the components of alternative therapies, adherence to the stated amounts of the components in alternative therapies is not routinely assessed. Isoflavones exist in two forms — aglycone (the free form) and glycosylated or glycone (the conjugated form) — the relative proportions of which vary between preparations. As glycosylation contributes considerably to the mass of isoflavone molecules, it is relevant to consider the total amount of potentially available isoflavone in alternative therapy preparations.

Isoflavone-containing preparations which had a recommended daily dose on their labels were purchased at random from pharmacies around Sydney during September 1999. Where possible, products from more than one manufacturing batch were purchased and all products were well within their stated shelf life. The tablets, capsules or powder were removed from their packaging to conceal their identity and randomly allocated to numbered plastic bags by the hospital pharmacy department. The samples were then sent to PhytoChem Technologies Inc (Chelmsford, Mass, USA), an independent reference laboratory for the assay of isoflavones. There, isoflavones were extracted within four months of purchase (and before their stated use-by date) from 500 mg of each specimen after dissolution in 70% methanol. Glycosylated and free isoflavones were assayed in duplicate by gradient high-pressure liquid chromatography, with detection of isoflavones at 254 nm using a Waters 996 series photodiode detector with a limit of detection of 0.2 µg/mL. The identity of chromatogram peaks was confirmed by UV–V spectral analysis, and by comparison with standards. The mobile phase was acetonitrile, and adequate peak separation, linearity, accuracy and reproducibility were demonstrated. The total amount of available aglycone isoflavones in each sample was estimated (see Table).

Only two products (Phytolife and Promensil) had total isoflavone contents close to the stated amount, and the content of the Phytolife product was variable. Estimated aglycone contents of preparations demonstrated that glycosylated isoflavones contributed substantially to the stated content of the product. A previous study of isoflavone-containing preparations marketed in the United States produced similar results to ours.1 Consumers may wish to consider not only whether an alternative therapy is of use, but also whether the product they purchase contains what they expect.