Folic acid is often used to treat anemia, which can be caused by a ‘hidden’ Vitamin B12 deficiency. Therefore, folic acid could theoretically ‘mask’ deficiencies of B12 deficiency, and the other symptoms of B12 deficiency will continue.

  Folic acid does not, however, treat nerve damage that B12 deficiency may cause, and permanent nerve damage may be caused if the B12 deficiency is not treated.

  Large amounts of folic acid actually can trigger the damaging effects of B12 deficiency, and should not be taken in quantities larger then 1000 μg/day.

  People taking folic acid supplements, especially adults over 50, should talk to their doctor about possible needs for additional B12 and monitor the amounts of folic acid they are consuming.

   Evidence of such ‘masking’ has not been consistently proven, and while it should be kept in mind it is not a major source of concern in the United States. The best way to prevent this type of B12 deficiency is by asking your physician to check B12 levels before taking a supplement containing folic acid.

• http://www.vitaminworld.com/vf/healthnotes/hn75_english/Concern/Vitamin_B12_Deficiency.htm
• http://www.publix.com/wellness/notes/Display.do?id=Supp&childId=Vitamin_B12