Foods Fortified With Folic Acid May Cut Stroke Risk
The B vitamin might work by reducing an amino acid in the blood, study finds
THURSDAY, March 16, 2006 (HealthDay News) -- Cereals and breads fortified with folic acid, mandatory in the United States and Canada to help reduce birth defects, may also help cut your risk of dying from a stroke, a new study suggests.
Folic acid has long been known for its effect on reducing certain birth defects when taken in sufficient quantities by pregnant women. That was the rationale behind the U.S. Food and Drug Administration's 1998 order for folic-acid fortification of enriched grain products such as cereals and breads. Canada made fortification mandatory that same year.
Now, experts have compared stroke mortality rates in both countries before and after fortification and found that death rates, while already on the decline before, dropped substantially after fortification took effect.
"This is the first population-based study of changes in stroke mortality before and after folic-acid fortification in the United States and Canada," said Quanhe Yang, an epidemiologist at the U.S. Center for Disease Control and Prevention's National Center on Birth Defects and Developmental Disabilities.
Yang is the lead author of the new study, which appears in the March 14 issue of Circulation.
The researchers also looked at stroke death rates in England and Wales, where fortification of foods with folic acid is not required, and did not find a significant change in mortality rates between the years 1990 and 2002.
What triggered the study? "There was accumulating evidence to suggest elevated levels of homocysteine [an amino acid in the blood] increases stroke death risk," he said. "It remains controversial." Some research has found that elevated homocysteine in the blood, by itself, can raise stroke risk, Yang said.
"If you have a high level of folic acid [in your blood], the level of homocysteine will decrease," he added.
Not all the evidence supports that view, however. Two studies released early on Sunday by the New England Journal of Medicine found that even after heart patients lowered their homocysteine levels via folic acid and B vitamin supplementation, their risk for heart attack did not change.
One study did find a "marginally significant" decrease in stroke risk linked to supplement use, while another found no decline in stroke and even a slight increase in heart attack risk after years of supplementation with folic acid and vitamins B6 and B12.
According to experts, the findings cast doubt on the conventional wisdom that folate might help ward off heart disease.
However, Yang's population-based study appears to support the traditional view on folate use. When he and his colleagues examined people before and after fortification became mandatory, they found that homocysteine levels -- and their risk of stroke death -- declined.
The researchers found an association, not a cause-and-effect, Yang emphasized. "The part we don't know is, if the folic acid directly reduces the risk of stroke. It may be that something happens in-between. We do not know yet the mechanism of homocysteine," he said, adding that folic acid somehow breaks down the amino acid.
For the study, Yang and his team reviewed national death statistics in the United States and Canada for the years 1990 to 2002. In the United States between 1990 and 1997, before fortification, the overall death rate from stroke declined by 0.3 percent each year. But from 1998 to 2002, the death rate declined 2.9 percent each year. Those findings translate to about 13,000 fewer stroke deaths each year among U.S. residents over age 40, the study said.
In Canada, the annual decline in stroke-related deaths was 1.2 percent among men and 0.9 percent for women over age 40 before fortification went into effect. After fortification, the declines were 5.6 percent for men age 40 and older and 5.4 percent for women 40 and above -- translating to 2,800 fewer stroke deaths each year after fortification.
Blood levels of folic acid have nearly doubled in the U.S. population since 1998, the authors noted.
Another expert familiar with the study findings called them potentially good news. In the past, researchers have looked at the effects of increasing folic acid on cardiovascular disease, including heart attacks and strokes, said Alice H. Lichtenstein, the Stanley Gershoff Professor of Nutrition at the USDA Human Nutrition Research Center at Tufts University in Boston. "The data for cardiovascular disease has not been encouraging," she said. "This [new study] is looking better."
But, like Yang, she stressed that the study only found an association, not a cause-and-effect. Don't go overboard on folic acid, she cautioned.
Currently, the recommended daily intake of folic acid -- also known as folate -- is 400 micrograms a day for adults and 600 for pregnant women. Many multivitamins contain 400 micrograms. Folate, a B vitamin, is also found in dark green leafy vegetables, fruits such as oranges and strawberries, and in fortified products.
To learn more about folic acid, visit the American Dietetic Association.