NEW YORK (Bloomberg) – Taking a daily supplement of folic acid and other B vitamins doesn't lower a woman's risk of cancer, a study of more than 5,000 women found.

Researchers found little difference in the number of women who developed cancer while on the supplements compared with those on a placebo, according to the study in this week's Journal of the American Medical Association. Low levels of folic acid was suspected to cause cancer by altering chemicals that affect DNA, changing how cells repair and divide, according to the American Cancer Society. Based on the latest finding, women should focus on eating healthy, exercising and quitting smoking to prevent cancer rather than on any identifiable supplements, said lead author Shumin Zhang.

"If we're just thinking of cancer prevention, there are other approaches," said Zhang, an associate professor of medicine at Harvard University and a researcher at Brigham and Women's Hospital in Boston, in a telephone interview.

Several studies suggest that dietary sources of folate, such as dark green leafy vegetables, may lower cancer risk, said study author JoAnn Manson, chief of Preventive Medicine at Brigham and Women's Hospital in Boston, in a statement. "Also, previous studies have shown conclusively that folic acid lowers the risk of certain birth defects, such as spina bifida, and adequate intake is important throughout pregnancy."

Researchers analysed data on cancer from a trial of 5,442 women health professionals ages 42 and older who had either pre- existing heart disease or carried three or more risk factors for coronary disease.

That trial studied if supplements of folic acid and vitamins B6 and B12 prevented heart disease in women at high risk for the condition versus a placebo.