Its synthetic form, folic acid, is added to enriched breads, breakfast cereals and other grains; this fortification has been required by law for the past decade, as studies have shown that folate before and during pregnancy can prevent neural tube defects -- birth defects of the brain and spine, such as spina bifida.

Folate is important in maintaining the DNA within cells, and some small studies have suggested that women who get more folate have a lower breast cancer risk.

However, when researchers at the University of Bristol in the UK combined the results from 22 studies on the subject, there was no evidence that the vitamin affected a woman's risk of the disease.

Along with this lack of benefit in human studies, some animal research has found high folate levels to actually feed the growth of breast tumors, lead study author Dr. Sarah J. Lewis told Reuters Health.

The bottom line, according to Lewis, is that women should be careful about taking large amounts of the vitamin until researchers know more about its effects on a range of disease risks.

Still, she said, women who might become pregnant should continue to get the recommended amount of folate to lower the risk of neural tube defects. Experts advise both men and women to get 400 mcg of folate per day, while pregnant women should have 600 mcg.

"We would urge women to carry on doing this," Lewis said.

She and her colleagues based their findings on observational studies -- studies in which researchers looked for associations between women's reported folate intake and breast cancer rates. Such studies are less definitive than clinical trials, in which participants are randomly assigned to take a treatment, such as folate, and then followed over time to monitor the health effects.

Lewis said the "best way" to determine the effects of folate on breast cancer would be to follow-up with the many women who, in the 1980s, took part in the clinical trials assessing folate and neural tube defects.

"We would urge those researchers involved in the randomized controlled trials to do this," she said.

SOURCE: Journal of the National Cancer Institute, November 15, 2006.

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Cancer stem cells start tumors in mice

Last Updated: 2006-11-20 11:52:00 -0400 (Reuters Health)

WASHINGTON - Stem cells -- the master cells that give rise to all the blood and tissue in the body -- may also be responsible for tumors, according to two separate studies published on Sunday.

Canadian and Italian researchers both found that specialized colon cancer stem cells appeared to be the sources of colon cancer tumors in mice.

Their findings, published in the journal Nature, support the idea that future cancer treatments will have to home in on cancer stem cells.

Similar findings have been seen for leukemia, breast and brain cancers, but the two studies are the first to show cancer stem cells are also responsible for colon tumors.

"Colon cancer is one of the best-understood neoplasms (tumors) from a genetic perspective, yet it remains the second most common cause of cancer-related death (in Canada), indicating that some of its cancer cells are not eradicated by current therapies," John Dick of University Health Network in Toronto and colleagues wrote in their report.

They implanted human colon cancer cells into mice with a deficient immune system -- a standard way of studying cancer.

Only certain cells, those with a protein on the surface called CD133, were able to initiate a new tumor.

CD133 had previously been implicated in brain and prostate cancers. In a second study, Ruggero De Maria of the Istituto Superiore di Sanita in Rome and colleagues got the same CD133 cells to start tumors when injected under the skin of immune-deficient mice.

"These studies demonstrate that a small population of colon cancer cells, distinct from those that make up the bulk of a tumor, initiate tumor growth," Nature said in a statement.

It may be possible to design drugs that attack only those cells, and thus treat colon cancer in a way that better affects the tumors without hurting healthy cells, the researchers said.

Colon cancer is the fourth most deadly cancer globally, killing 655,000 people a year, according to the World Health Organization.

Copyright © 2006 Reuters Limited. All rights reserved. Republication or redistribution of Reuters content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters. Reuters shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon. Reuters and the Reuters sphere logo are registered trademarks and trademarks of the Reuters group of companies around the world.