Researchers reviewed data from nearly 6 million births in Canada. The births occurred between 1990 and 2011. Folic acid food fortification became mandatory for all types of flour, enriched pasta and cornmeal in 1998 in Canada.
During the study period, there was an 11 percent decline in rates of congenital heart defects overall. But decreases weren't seen in all types of heart defects present at birth.
The biggest declines -- between 15 percent and 27 percent -- were in structural defects of the heart, such as holes in the wall of the heart or a narrowing of the major artery (the aorta) that carries blood to the body from the heart, the investigators found.
But, there was no reduction in heart defects at birth caused by an abnormality in the number of an infant's chromosomes, the findings showed.
An estimated 650,000 to 1.3 million children and adults in the United States have congenital heart disease, the researchers said. A hole in the wall of one of the heart's ventricles is the most common type of defect in children. These defects account for nearly 620,000 of the cases, the researchers added.
Folic acid deficiency during pregnancy can cause a number of complications. These include anemia and neural tube defects (such as spina bifida, an abnormality of the spine and spinal cord), the researchers explained.
Women who are likely to get pregnant should start taking folic acid supplements before conceiving because they may not get enough folic acid from their diet alone, said study senior author Dr. K.S. Joseph. He's a professor of obstetrics and gynecology at the University of British Columbia in Vancouver.
Joseph added that the study findings likely apply to the U.S. population as well. That's because the United States began fortifying foods with folic acid around the same time as Canada, he said.
Although the study found an association between folic acid food fortification and a decline in certain heart-related birth defects, it did not prove a cause-and-effect relationship.
The study was published Aug. 29 in the journal Circulation.
The March of Dimes has more on folic acid.
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