A new study has found that several hundred children a year in Canada could be spared devastating forms of cancer if women who are pregnant or trying to conceive take a multivitamin fortified with folic acid.

The Canadian research is believed to be the largest of its kind ever undertaken. It shows that expectant women who take the supplement during the first trimester of pregnancy can lower the risk of leukemia, brain tumours or neuroblastoma by as much as 47 per cent.

"This is very meaningful, because these cancers are devastating for the child. Many of them die," says Dr. Gideon Koren, the study's principal investigator and director of the Motherisk Program at Toronto's Hospital for Sick Children.

"Those who survive have very long-term effects from the treatments, and of course the cost on the family and health system is huge. Here is a very, very cheap way to prevent a large percentage of them."

The study was partly funded by Duchesnay Inc., which makes the prenatal multivitamin PregVit. Koren has also received funding from Duchesnay.

Folic acid alone had already been proven to reduce the risk of neural tube defects - defects of the brain and spine, including spina bifida. Rates of neural tube defects have been falling since Canada began in 1998 requiring breads, flours and other foods be enriched with folic acid.

Last year, the Sick Kids team, working with researchers from London, Ont., reported that folic-acid fortified multivitamin supplements consistently protect babies against other congenital anomalies, including "holes in the heart," limb defects, cleft palate and hydrocephalus - water buildup on the brain that can lead to irreversible brain damage.

The new study found the multivitamins were associated with a 47 per cent risk reduction for neuroblastoma, 39 per cent for leukemia and 27 per cent for brain tumours.

"These are significant. It means in the case of neuroblastoma cutting half of the cases in the country. In the case of leukemia, cutting 40 per cent," Koren says.

Combined, the three cancers affect about 1,000 Canadian children each year, Koren says.

Neuroblastoma is one of the most devastating cancers in the young. These solid tumours can occur anywhere in the body but usually arise from the adrenal gland, which sits just above the kidney.

"Unfortunately, it's frequently discovered when it is already advanced," said Dr. Paul Rogers, head of the division of pediatric hematology and oncology at B.C. Children's Hospital and the University of British Columbia. Neuroblastoma affects one in every 6,000 to 7,000 children in North America.

Leukemia, on the other hand, accounts for 25 to 35 per cent of new childhood cancer cases each year, making it the most frequently diagnosed pediatric cancer.

It's not known which vitamins or minerals, and in what amounts, could be protecting babies from cancer. But it's possible folic acid, which plays a crucial role in cellular function, may be acting alone. One theory is that a shortage of folic acid may impair DNA synthesis and repair, or change the way genes that normally suppress cancer, or turn cancer on, are read.

"A few studies from the U.S. say that if you talk to mums who have kids with cancers, it is much more likely that they did not use vitamins," Koren said in an interview.

"We thought that was important enough to pull together anything which was done by anyone, anywhere."

His team combined the results of seven studies "where mums (of children with cancer) were asked, 'What did you use in pregnancy?' in a very detailed manner and this was compared to the next mom who had a child with no cancer, who was healthy."

The study, published online Wednesday in the journal Clinical Pharmacology & Therapeutics, estimates prenatal multivitamin supplements "may prevent 900 cases of pediatric leukemia and 300-400 cases of pediatric brain tumours annually in the United States."

Only 40 to 50 per cent of take prenatal vitamins.