Folic Acid

Though supplements containing 0.8 mg of folic acid are available over-the-counter, tablets and injectable forms that contain more than 1 mg of folic acid are available only with a prescription. The vitamin is used to treat anaemia caused by folic acid deficiency, which may result from poor absorption, a dietary deficiency, or pregnancy.

Summary of Interactions with Vitamins, Herbs, and Foods
In some cases, an herb or supplement may appear in more than one category, which may seem contradictory. For clarification, read the full article for details about the summarized interactions.

Beneficial May be Beneficial: Depletion or interference—The medication may deplete or interfere with the absorption or function of the nutrient. Taking these nutrients may help replenish them.

Zinc
Beneficial May be Beneficial: Supportive interaction—Taking these supplements may support or otherwise help your medication work better.

Vitamin B6
Avoid Avoid: Reduced drug absorption/bioavailability—Avoid these supplements when taking this medication since the supplement may decrease the absorption and/or activity of the medication in the body.

Alcohol

Antacids

Beans

Food

Smoking

Vitamin B6
Side effect reduction/prevention

None known
Adverse interaction

None known

An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.

Interactions with Dietary Supplements

Vitamin B6
Folic acid and vitamin B6 have been used to reduce elevated blood levels of homocysteine, which has been associated with atherosclerosis. One controlled study showed that taking 0.3 mg of folic acid together with 120 mg of vitamin B6 reduced homocysteine levels more than taking either vitamin alone. The study also revealed that long-term supplementation with vitamin B6 alone might reduce blood folic acid levels.1 Therefore, people with elevated blood homocysteine levels should supplement with both folic acid and vitamin B6.

Zinc
Though some studies indicate that supplementing with folic acid reduces blood levels of zinc, most show no interaction between the two nutrients when folic acid is taken at moderate levels.2 Therefore, until more convincing evidence is available, people taking moderate amounts of folic acid do not need to supplement with zinc. Zinc supplementation is recommended when folic acid intake is high. A doctor should be consulted to determine the appropriate time to add zinc supplementation to folic acid therapy.

Interactions with Foods and Other Compounds

Food
Studies have shown that taking folic acid with different foods can alter the absorption of the vitamin. One study showed that taking folic acid supplements with wheat bran fibre increased, while beans reduced absorption of the vitamin.3 Though it is unlikely that either food will clinically affect folic acid absorption from a mixed diet, people should probably avoid taking the vitamin with a meal consisting primarily of beans. Another study revealed that folic acid is better absorbed on an empty stomach, though a light meal only slightly reduced absorption.4

Alcohol
One study showed that the majority of individuals who chronically consume alcohol have below-normal red blood cell levels of folic acid.5 Though lower intake of foods containing folic acid may be involved, some researchers believe that alcohol may directly reduce blood levels of nutrients.6 Animal studies have shown that chronic alcohol consumption might reduce absorption7 or increase elimination of folic acid.8 Studies involving acute consumption of alcohol in humans have shown that alcohol may increase urinary elimination of folic acid.9 Additional studies are needed to determine whether heavy drinkers taking folic acid might require larger-than-normal amounts of the vitamin to treat anaemia.

Antacids
One controlled study showed that taking folic acid together with an antacid containing aluminium and magnesium hydroxide reduced the absorption of the vitamin.10 Therefore, individuals should take folic acid one hour before or two hours after taking antacids containing aluminium and magnesium hydroxide.

Smoking
A study of individuals aged 65 and older revealed that people who smoke cigarettes have lower red cell and blood folic acid levels compared with those who do not smoke.11 Lower intake of folic acid through food only partly explained the reduced blood levels observed in smokers. Additional research is needed to determine whether smokers taking folic acid might need to take larger-than-normal amounts of the vitamin to treat anaemia.

References

1. Mansoor MA, Kristensen O, Hervig T, et al. Plasma total homocysteine response to oral doses of folic acid and pyridoxine hydrochloride (vitamin B6) in healthy individuals. Oral doses of vitamin B6 reduce concentrations of serum folate. Scand J Clin Lab Invest 1999;59:139–46.

2. Campbell RC. How safe are folic acid supplements? Arch Intern Med 1996;156:1638–44 [review].

3. Keagy PM, Shane B, Oace SM. Folate bioavailability in humans: effects of wheat bran and beans. Am J Clin Nutr 1988;47:80–8.

4. Pfeiffer CM, Rogers LM, Bailey LB, Gregory JF 3rd. Absorption of folate from fortified cereal-grain products and of supplemental folate consumed with or without food determined by using a dual-label stable-isotope protocol. Am J Clin Nutr 1997;66:1388–97.

5. Gloria L, Vravo M, Camilo ME, et al. Nutritional deficiencies in chronic alcoholics: relation to dietary intake and alcohol consumption. Am J Gastroenterol 1997;92:485–9.

6. Simko V, Connel AM, Banks B. Nutritional status in alcoholics with and without liver disease. Am J Clin Nutr 1982;35:197–203.

7. Romero JJ, Tamura T, Halsted CH. Intestinal absorption of 3H-folic acid in the chronic alcoholic monkey. Gastroenterology 1981;80:99–102.

8. McMartin KE, Collins TD. Role of ethanol metabolism in the alcohol-induced increase in urinary folate excretion in rats. Biochem Pharmacol 1983;32:2549–55.

9. McMartin KE, Collins TD, Shiao CQ, et al. Study of dose-dependence and urinary folate excretion produced by ethanol in humans and rats. Alcohol Clin Exp Res 1986;10:419–24.

10. Russell RM, Golner BB, Krasinski SD, et al. Effect fo antacid and H2 receptor antagonists on the intestinal absorption of folic acid. J Lab Clin Med 1988;112:458–63.

11. Walmsley CM, Bates CJ, Prentice A, Cole TJ. Relationship between cigarette smoking and nutrient intakes and blood status indices of older people living in the UK: further analysis of data from the National Diet and Nutrition Survey of people aged 65 years and over, 1994/95. Public Health Nutr 1999;2:199–208.