From Howard Jacobs, University College London
Marina Delac makes the argument in her letter that hormone replacement therapy based on the two hormones oestrogen and progesterone might be safer if women took the natural “bio-identical” hormone progesterone instead of the synthetic progestins usually prescribed (29 March, p 29). But as she correctly points out, the bio-identical progesterone preparations that are available have never been tested in large-scale trials, so no one knows whether they are indeed safer.
I have come across one trial done in 1998, but the results were not convincing. To be effective, progesterone or its synthetic equivalents must reach and protect the uterus to prevent it turning cancerous through overexposure to oestrogen. But when the bio-identical progesterone was applied to the skin as a cream, not nearly enough diffused into blood to protect the uterus. This is hardly surprising, given that the skin contains 5-reductase, an enzyme which destroys progesterone.
Unless a way can be found to make bio-identical progesterone as resistant to enzyme destruction as its hardier synthetic cousins, it looks as though the commercial preparations are the only reliable ones for now.
London, UK
