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Reviewed by the Faculty of Harvard Medical School

Folic Acid: Time To Supplement?

In 1998, the U.S. Food and Drug Administration added folic acid to the list of vitamins and minerals added to the nation's food supply. The intent was to prevent devastating neural tube birth defects, which afflict as many as one in 1,000 newborns. An unintended but fortuitous side effect might be a significant drop in the rate of heart disease among older Americans. Recent research provides mixed results.

The Role Of Folic Acid In Fetal Development

Studies from the Centers for Disease Control and Prevention established that 50% to 70% of neural tube abnormalities, which produce profound and often fatal neurologic defects, can be prevented by ensuring that pregnant women get at least 0.4 milligram of folic acid each day throughout the first trimester of pregnancy. Without supplementation, most women would fall short of the mark.

Public health officials reasoned that if the vitamin were added to grain products, such as flour, pasta, bread and breakfast cereals, women would get more of the folic acid they need, when they need it. But there's a limit to the amount of folic acid that can be safely added to food. High levels of folic acid can mask early symptoms of pernicious anemia, a deficiency of vitamin B-12 common among older people. If the weakness, fatigue and dizziness that characterize the early stages of pernicious anemia are suppressed and the disease is not diagnosed, pernicious anemia will ultimately cause irreversible neurologic damage.

In a compromise, the FDA decided to limit the amount of folic acid added to food. A bowl of breakfast cereal, for instance, provides only about 0.1 milligram. Most women of childbearing age do not consume enough folic acid to prevent neural tube defects. All women of childbearing age should take a vitamin containing at least 0.4 milligrams of folic acid. Folic acid supplementation may also be important for women who do not intend to get pregnant and for men as well. Here's why.

A Possible Heart Connection

Thirty years ago, scientists discovered a genetic defect called hyperhomocysteinemia, which impairs the body's ability to break down the amino acid homocysteine. When a person inherits two copies of the defective gene, the amino acid can build up to levels 40 times higher than normal. At such high levels, homocysteine is extremely toxic to blood vessels, resulting in clogged arteries (atherosclerosis) and fatal heart attack or stroke, often by age 15. That scenario is rare, occurring in just one of every 200,000 births. However, 5% to 7% of Americans carry a single copy of the hyperhomocysteinemia gene. For those people, blood levels of homocysteine are two to four times higher than normal, typically causing cardiovascular disease by early middle age.

Studies then have shown that consuming folic acid, either alone or in combination with vitamins B-6 and B-12, can significantly reduce homocysteine levels.

The key question is: Does lowering blood homocysteine by taking extra folic acid and B vitamins reduce the risk for cardiovascular disease? Researchers don't know the answer yet. Due to some discouraging research results, experts are no longer quite so confident that lowering homocysteine levels reduces a person's heart disease risk. However, because the risks and costs of taking a daily multivitamin with at least 0.4 mg of folic acid are so low, most experts believe that taking multivitamins might still be the way to go.

Here's what doctors know for sure. People who eat more vegetables and fruits, and less saturated fat, and who exercise, have lower risks of heart attacks.

Folic Acid In Food

Supplements aren't the only way to make sure you get plenty of this important B vitamin. Here are some of the top folic-acid-rich foods.

Food Folic acid (milligrams)
Chicken giblets, 3.5 ounces 0.38
Beans, most types, cooked, 1 cup 0.26
Turnip greens, cooked, 1/2 cup 0.17
Avocado, 1 medium 0.16
Okra, cooked, 1/2 cup 0.13
Asparagus, cooked, 1/2 cup 0.13
Breakfast cereal, fortified, 1 cup 0.11
Orange juice, 1 cup 0.11
Spinach, cooked, 1/2 cup 0.10
Source: USDA Nutrition Database



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