The B vitamin folate has important health benefits, but a lower risk of breast cancer may not be one of them, new research suggests.

In an analysis of 22 past studies, researchers found no evidence that higher folate intake was related to a lower breast cancer risk.

Across the studies, women’s cancer risk remained virtually unchanged with every 100 microgram (mcg) increase in daily folate, the study authors report in the Journal of the National Cancer Institute.

Folate is found naturally in greens like spinach and broccoli, oranges and orange juice, and dried beans and peas, among other foods.

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.