Can you have too much folic acid?

The risk of toxicity from folic acid is low.

The Institute of Medicine has established a tolerable upper intake level (UL) for folate of 1 mg for adult men and women, and a UL of 800 µg for pregnant and lactating (breast-feeding) women less than 18 years of age.

Masking Vitamin B12 deficiency

Supplemental folic acid should not exceed the UL to prevent folic acid from masking symptoms of vitamin B12 deficiency.There has been concern about the interaction between vitamin B12 and folic acid. 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 could theoretically occur if vitamin B12 deficiency is not treated. Therefore, intake of supplemental folic acid should not exceed 1000 micrograms (1000 mcg or 1 mg) per day to prevent folic acid from masking symptoms of vitamin B12 deficiency. In fact, to date the evidence that such masking actually occurs is scarce, and there is no evidence that folic acid fortification in Canada or the US has increased the prevalence of vitamin B12 deficiency or its consequences.

However one recent study has demonstrated that high folic or folate levels when combined with low B12 levels are associated with significant cognitive impairment among the elderly, If the observed relationship for seniors between folic acid intake, B12 levels, and cognitive impairment is replicated and confirmed, this is likely to re-open the debate on folic acid fortification in food. While public health policies tend generally to support the developmental needs of infants and children over slight risks to other population groups, the ratio of benefit in this case is likely to be on the scale of one child's life saved versus impairment of hundreds or thousands of seniors.

In any case, it is 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.

Folic Acid and Malaria

Research suggests high levels of folic acid can interfere with some antimalarial treatments.
Folicacid might have a preventative effect on a number of other diseasessuch as heart diseases or stroke (millions affected), but this positiveeffect is not yet proven.