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Soy Shouldn't Increase Cancer Risk, Study Finds

Posted on: Sunday, 15 January 2006, 18:00 CST

The possible role of plant estrogens from soy products in stimulating breast cancer cells has rumbled through the research community and health foods industry for several years.

There's been a mixed bag of study results from mice and humans. One report showed that soy proteins promoted breast cancer in mice lacking ovaries, and thus not producing much estrogen on their own. Another study on mice with ovaries intact found that soy inhibited tumor growth.

And human population studies have found that women who consumed diets high in soy generally have lower rates of breast cancer.

A study published Sunday in the journal Cancer Research may not settle the soy question for all women. But based on a complex test involving monkeys, it suggests that plant estrogens should not increase the risk of breast cancer in postmenopausal women, and may provide some protection to some women taking estrogen supplements.

"Even at high doses, we found no evidence that the estrogen-like compounds in soy, called isoflavones, stimulate cell growth or other markers for cancer risk in breast tissue,'' said Charles Wood, a veterinarian researcher at Wake Forest University Baptist Medical Center and lead author of the study.

"The study also suggests that women who have higher levels of estrogen may actually gain a protective effect from higher doses of soy isoflavones,'' he added.

Wood and his colleagues evaluated the soy proteins' effect in the presence of different levels of estrogen by rotating 31 postmenopausal cynomolgus monkeys through eight different diets. Each diet contained one of four different isoflavone doses along with either a low or high dose of estrogen.

The isoflavone doses were equivalent to these human levels: no isoflavones, 60 milligrams (the typical Asian diet), 120 milligrams (the highest level that can be achieved through diet alone) and 240 milligrams (levels obtained through supplements).

Estrogen doses were designed to mimic either a low or high-estrogen environment found in postmenopausal women. Those levels can vary depending on a women's amount of body fat, which produces estrogen, and whether they are taking hormone replacement therapy.

The researchers found that in the low-estrogen environment, there was no evidence of increased breast cell proliferation or other markers of breast cancer risk at any level of isoflavone exposure, even at doses several times higher than the typical Asian diet.

In a high estrogen environment, there was higher breast cell proliferation both when isoflavones weren't in the diet and when they were present in lower doses. However, the addition of high levels of soy isoflavones tended to block estrogen effects in breast tissue.

"For women at increased risk of breast cancer due to higher estrogen levels, a diet high in soy isoflavones may offer a modest breast protective effect,'' said Wood.

But he cautioned that the study may not apply to women who have not gone through menopause and thus have higher and more dynamic hormone levels, or to women who are taking combined hormone therapy with estrogen and progestin.

On the Net: http://www.cancerres.aacrjournals.org/

www.wfubmc.edu

(Contact Lee Bowman at BowmanL(at)SHNS.com.)

© 2005 Scripps Howard News Service.

All Rights Reserved.

Source: Scripps Howard

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