LONDON (Reuters Health) - A researcher said on Tuesday that so little is known about how plant oestrogens act on the human body that sales of soy supplements as a natural alternative to hormone replacement therapy (HRT) must be questioned.

But Dr. Saffron Whitehead, reader in reproductive physiology at St. George's Hospital Medical School, London, said new studies on human cells have shown that genistein and other phyto-oestrogens may also stop the enzymes that make these hormones.

She told the British Endocrine Society's annual meeting in Harrogate, Yorkshire, this could explain why the incidence of breast cancer, which in many cases is dependent on oestrogen, is about two-thirds lower amongst Japanese and Chinese women who consume diets rich in soy compared with women living in England.

Whitehead's team examined the effects of phyto-oestrogens on human ovarian cells obtained during procedures for in vitro fertilization.

The results showed that several phyto-oestrogens, including genistein, inhibited the conversion of androgens to oestrogens.

The researchers believe this could be significant in postmenopausal women because as these women's ovaries cease to function, their only source of oestrogens is converting androgens released by their adrenal glands.

"This finding is potentially important to the phyto-oestrogen story," Whitehead added in a statement. "We really don't know how phyto-oestrogens act in the human body. They could be weak oestrogen mimics, oestrogen blockers or enzyme inhibitors.

"If they do stop the natural production of oestrogens, we should consider whether soy supplements be sold as a natural alternative to HRT."

Reference Source 89

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