The research, which analyzed data from seven international studies that involved thousands of children, should encourage more mothers to take prenatal vitamins, says Dr. Gideon Koren, the study's principal investigator.

"That's why we are so excited," says Koren, director of the Motherisk program at the hospital and a professor of pediatrics at the University of Toronto.

The study found a multivitamin regime fortified with folic acid, a member of the B-complex group of vitamins, lowered the chance a child would develop a brain tumour by 27%, leukemia by 39% and neuroblastoma by 49%. It was published yesterday in the journal Clinical Pharmacology and Therapeutics.

For 15 years it has been common knowledge that the risk of spina bifida, a malformation of the spine, can be reduced by as much as 80% when mothers take folic acid prior to and during pregnancy.

Even so, Koren says only 40% of Canadian mothers bother to take the nutrient, which costs pennies a day.

Most prenatal supplements supply between 600 and 1,000 micrograms of folic acid. While a diet rich in folic acid (found naturally in dark green vegetables, beans, citrus fruit and berries, as well as fortified bread and cereal) would likely provide the recommended daily allowance of 400 micrograms a day, a supplement is still recommended for pregnant women.

Jana Atkins doesn't need any urging.

The Toronto woman began taking folic acid and vitamins before her first pregnancy, now in its 35th week, to prevent spina bifida.

"Maybe many people haven't heard of spina bifida, whereas cancer is a catch-all phrase and it's a disease that we're all well aware of," says the 32-year-old psychologist-in-training.

The study grew out of an observation by oncologists at Sick Kids who noticed the number of neuroblastomas began to drop substantially about five years ago. A devastating cancer of the peripheral nervous system, the disease affects about one in every 6,500 children under five years in North America.

The only link Koren and colleagues could suggest was a Health Canada edict that forced flour manufacturers to add folic acid to their products in 1998.

A subsequent study, published by Koren three years ago, showed neuroblastoma had substantially decreased in Ontario after the fortified flour was introduced.

While the Ontario study focused on neuroblastomas, the international studies also looked at leukemia and brain tumours.

Since some studies included both multivitamins and folic acid, there is some doubt as to which supplement is tied to the cancer protection.

"To our amazement and surprise, all available studies today from different parts of the world ... showed a similar trend (to the one in Ontario)," Koren says.

Koren says folic acid, instrumental in the body's DNA repair mechanisms, is likely at play because damaged DNA is a key contributor to tumour development, though he did not rule out the role played by other vitamins -- including A, the B series, C, D, E as well as iron.