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Soya cuts cancer threat of HRT
Soya beans
Soya beans could stop hormones triggering cancer
Soya may protect women against the cancer risk linked with hormone replacement therapy, scientists have claimed.

However, they warn that the wrong balance between soya consumption and HRT dosage may have the opposite effect and increase the risk.

HRT has been associated with a higher than normal incidence of breast or uterine cancer.

This is because oestrogen, the female sex hormone that is given to women undergoing HRT, can trigger the development of cancerous tumours.

Soya contains plant versions of another female sex hormone, called phytoestrogens, which are thought to block the action of oestrogen on breast and uterus cells.

Professor Mark Cline, from Wake Forest University Baptist Medical Center in Winston-Salem, North Carolina, USA, showed that soya could protect postmenopausal monkeys from developing cancer.

Hormone replacement therapy induced a proliferation of cells - a precursor of cancer - in the breasts and wombs of the monkeys.

But when they were fed soya of the sort found in tofu and dietary supplements the cells stopped multiplying so rapidly.

"These data indicate that soy supplements may decrease breast and endometrial (uterine) cell proliferation and therefore could decrease cancer risk in these tissues," said Professor Cline, who presented his findings at the annual meeting of the American Association for the Advancement of Science in Anaheim, California.

Possible risks

Breast scan
Hormone replacement therapy can increase the risk of breast cancer
However, Profesor Cline warned that tests in rats whose ovaries had been removed revealed that when the animals were given low doses of oestrogen replacement, the addition of natural soya to their diet increased breast cell proliferation.

At higher HRT doses, however, soya reduced cell proliferation in both the breast and uterus.

Professor Cline said further work was needed to explore the basic mechanisms by which soya phytoestrogens affected the incidence of breast cancer.

"Widespread consumption of phytochemicals in the human diet and as supplements make it imperative that we understand their effects, particularly as they relate to differing developmental and functional stages of the breast," he added.

He drew attention to the fact that Asians living in their native country had far lower cancer rates than Americans, probably because of their diet which contained a high proportion of vegetables, including soya.

American-born children of Asian immigrants had a 60% higher risk of developing breast cancer than people who had moved to the United States from Asia and were now eating western diets.

This implied that dietary effects protecting against breast cancer may occur early in life.

However, the degree to which the anti-cancer properties of vegetables could be attributed to phytoestrogens was unclear.

Professor Cline said: "The benefit of soy phytoestrogens is clearer for dietary exposures early in life and for pre-menopausal women. The benefit for older women and breast cancer survivors remains to be determined."

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