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Folic Acid

Also indexed as:Vitamin B9

Possible Deficiencies

Many people consume less than the recommended amount of folic acid. Scientists have found that people with heart disease commonly have elevated blood levels of homocysteine, a laboratory test abnormality often controllable with folic acid supplements. This suggests that many people in Western societies have a mild folic acid deficiency. In fact, it has been suggested that increasing folic acid intake could prevent an estimated 13,500 deaths from cardiovascular diseases each year.⁹⁵

Folic acid deficiency has also been common in alcoholics, people living at poverty level, those with malabsorption disorders or liver disease (e.g., cirrhosis), and women taking the birth control pill. Recently, elderly people with hearing loss have been reported to be much more likely to be folic acid deficient than healthy elderly people.⁹⁶ A variety of prescription drugs including cimetidine, antacids, some anticancer drugs, triamterene, sulfasalazine, and anticonvulsants interfere with folic acid.

Deficiency of folic acid can be precipitated by situations wherein the body requires greater than normal amounts of the vitamin, such as pregnancy, infancy, leukemia, exfoliative dermatitis, and diseases that cause the destruction of blood cells.⁹⁷

The relationship between folic acid and prevention of neural tube defects is partly thought to result from the high incidence of folate deficiency in many societies. To protect against neural tube defects, the U.S. Food and Drug Administration has mandated that some grain products provide supplemental folic acid at a level expected to increase the dietary intake by an average of 100 mcg per day per person. As a result of folic acid added to the food supply, fewer Americans will be depleted compared with the past. In 1999, scientific evidence began to demonstrate that the folic acid added to the U.S. food supply was having positive effects, including a partial lowering of homocysteine levels.⁹⁸ In the same year, however, a report from the North Carolina Birth Defects Monitoring Program suggested the current level of folic acid fortification has not reduced the incidence of neural-tube defects.⁹⁹ Many doctors and the Centers for Disease Control in Atlanta¹⁰⁰ believe that optimal levels of folic acid intake may still be higher than the amount now being added to food by several hundred micrograms per day. A low blood level of folate has also been associated with an increased risk of miscarriage.¹⁰¹

People with kidney failure have an increased risk of folic acid deficiency.¹⁰² Recipients of kidney transplants often have elevated homocysteine levels, which may respond to supplementation with folic acid.¹⁰³ The usual recommended amount of 400 mcg per day may not be enough for these people, however. Larger amounts (up to 2.4 mg per day) may produce a better outcome, according to one double-blind trial.¹⁰⁴

Folate deficiency is more prevalent among elderly African American women than among elderly white women.¹⁰⁵

Side Effects

With the exception of rare cases of allergic reactions,¹⁰⁶ folic acid is not generally associated with side effects,¹⁰⁷ although there have been rare case reports of allergic reactions to the vitamin.¹⁰⁸ Folic acid supplementation can interfere with the laboratory diagnosis of vitamin B12 deficiency, possibly allowing the deficiency to progress undetected to the point of irreversible nerve damage.¹⁰⁹ Although vitamin B12 deficiency is uncommon, no one should supplement with 1,000 mcg or more of folic acid without consulting a doctor.

In a double-blind trial, people with diabetes who also had with kidney disease received a daily placebo or 2.5 mg of folic acid, 1 mg of vitamin B12, and 25 mg of vitamin B6 for three years. Compared with the placebo, vitamin supplementation accelerated the decline in kidney function and increased the incidence of cardiovascular events (such as heart attacks) and heart disease-related deaths.¹¹⁰ Based on this study, diabetics with kidney disease should not take these vitamins without a doctor's supervision.

Vitamin B12 deficiencies often occur without anemia (even in people who do not take folic acid supplements). Some doctors do not know that the absence of anemia does not rule out a B12 deficiency. If this confusion delays diagnosis of a vitamin B12 deficiency, the patient could be injured, sometimes permanently. This problem is rare and should not happen with doctors knowledgeable in this area using correct testing procedures.