The medical evidence on the pros and cons of folic acid supplementation keeps getting murkier and murkier.
A new study by researchers at St. Michael's Hospital in Toronto showed that giving folic acid supplements to pregnant and breast-feeding rats reduced the rate of colon cancer in their offspring by 64 per cent. The findings were published in the journal Gut.
But a study published back in February by the same team found that daughters of rats who were given folic acid supplements before conception, during pregnancy and while breast feeding have breast cancer rates twice as high as the offspring of other rats who did not get supplements.
These studies add to the sometimes contradictory body of evidence on folic acid - the synthetic form of folate, a B vitamin found in green leafy vegetables, legumes and oranges.
"What this is telling us is that folic acid can have drastically different effects on different organ systems in our bodies," said Young-in Kim, the scientist who led both of the St. Mike's studies. "It may be protective in certain organs and it may be harmful in other organs."
Despite the mixed signals on cancer, the research clearly shows that folate is crucial for the prevention of certain birth defects such as spina bifida. Since 1998, food manufacturers in Canada and the United States have been required by law to add folic acid to bread, pasta, flour and other grain products. The fortification effort is meant to ensure that women who are of child-bearing age receive adequate levels of folic acid.
Dr. Kim noted that fortifying foods with folic acid has been highly successful in reducing birth defects. But he is concerned that some people may now be consuming excessive levels of folic acid from other sources, such as supplements.
"We really need to monitor the effects of too much folic acid," said Dr. Kim. He added that more studies are need to clarify its potential role on cancer risk.