Caution About Folic Acid Supplements

Beware of the interaction between vitamin B₁₂ and folic acid
Intake of supplemental folic acid should not exceed 1,000 micrograms (μg) per day to prevent folic acid from triggering symptoms of vitamin B₁₂ deficiency . Folic acid supplements can correct the anemia associated with vitamin B₁₂ deficiency. Unfortunately, folic acid will not correct changes in the nervous system that result from vitamin B₁₂ deficiency. Permanent nerve damage can occur if vitamin B₁₂ deficiency is not treated.

It is very important for older adults to be aware of the relationship between folic acid and vitamin B₁₂ because they are at greater risk of having a vitamin B₁₂ deficiency. If you are 50 years of age or older, ask your physician to check your B₁₂ status before you take a supplement that contains folic acid. If you are taking a supplement containing folic acid, read the label to make sure it also contains B₁₂ or speak with a physician about the need for a B₁₂ supplement.

What is the health risk of too much folic acid?

Folate intake from food is not associated with any health risk. The risk of toxicity from folic acid intake from supplements and/or fortified foods is also low. It is a water soluble vitamin, so any excess intake is usually excreted in urine. There is some evidence that high levels of folic acid can provoke seizures in patients taking anti-convulsant medications. Anyone taking such medications should consult with a medical doctor before taking a folic acid supplement.

The Institute of Medicine has established a tolerable upper intake level (UL) for folate from fortified foods or supplements (i.e. folic acid) for ages one and above. Intakes above this level increase the risk of adverse health effects. In adults, supplemental folic acid should not exceed the UL to prevent folic acid from triggering symptoms of vitamin B₁₂ deficiency. It is important to recognize that the UL refers to the amount of synthetic folate (i.e. folic acid) being consumed per day from fortified foods and/or supplements. There is no health risk, and no UL, for natural sources of folate found in food. Table 4 lists the Upper Intake Levels (UL) for folate, in micrograms (μg), for children and adults.

Table 4: Tolerable Upper Intake Levels for Folate for Children and Adults

Age (years)	Males and Females (μg/day)	Pregnancy (μg/day)	Lactation (μg/day)
1-3	300	N/A	N/A
4-8	400	N/A	N/A
9-13	600	N/A	N/A
14-18	800	800	800
19 +	1000	1000	1000

Selecting a healthful diet

As the 2000 Dietary Guidelines for Americans states, "Different foods contain different nutrients and other healthful substances. No single food can supply all the nutrients in the amounts you need". Green leafy vegetables, dried beans and peas, and many other types of vegetables and fruits provide folate. In addition, fortified foods are a major source of folic acid. It is not unusual to find foods such as some ready-to-eat cereals fortified with 100% of the RDA for folate. The variety of fortified foods available has made it easier for women of childbearing age in the US to consume the recommended 400 mcg of folic acid per day from fortified foods and/or supplements. The large numbers of fortified foods on the market, however, also raises the risk of exceeding the UL. This is especially important for anyone at risk of vitamin B₁₂ deficiency, which can be triggered by too much folic acid. It is important for anyone who is considering taking a folic acid supplement to first consider whether their diet already includes adequate sources of dietary folate and fortified food sources of folic acid.