Beware of the interaction between vitamin B12 and folic acid
Intake of supplemental folic acid should not exceed 1,000 micrograms (?g) 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 lost in the 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 (?g), for children and adults.
Table 4: Tolerable Upper Intake Levels for Folate for Children and Adults 
|Males and Females