Supplementing with B12: Vitamin Side Effects?

Are there any potential side effects to taking supplemental vitamin B12?

Although the body's daily needs for vitamin B12 can be measured in millionths of a gram, vitamin B12 is extraordinarily non-toxic. In fact, when the RDA's for vitamins were established, scientists did not bother to set an upper limit to how much vitamin B12 it is safe to take. Even 1 gram (which is to say, one million micrograms) per day day is non-toxic.

Where you might run into problems with vitamin B12, however, is masking vitamin B12 needs by taking too much folate.

In a condition called pernicious anemia, the body fails to make well-formed red blood cells because of a deficiency of folic acid and B12. It's possible to treat the anemia with folic acid alone, leaving the B12 deficiency. If you do this, however, you can then suffer a number of vitamin B12-deficiency conditions (potentially, dementia, neuropathy, tingling in the legs, tingling in the arms, difficulty in concentration, memory lapses, mood swings, and Alzheimers-like states) that could be avoided simply by replacing both B vitamins at the same time. Just 3 micrograms (3 millionths of a gram) a day, however, is enough vitamin B12 to prevent deficiency.

So, where can you go wrong? Where you can get into trouble is trying to make up a specific B-vitamin deficiency with an all-purpose vitamin B pill. Generally speaking, it's best to get a blood test to make sure you know exactly what vitamins you need, and then supplement those just enough to bring you up to optimal health. And to avoid getting too much folate, don't get all your vitamin B-12 from an all-purpose vitamin B supplement.