How Much Vitamin B12 Should You Take? B12 Blood Test Info

Vitamin B12 is pretty darn important to our health, but how much vitamin B12 should you take? Better yet, is there a B12 blood test to see if you are deficient?

Vitamin B12 is a critically important nutrient.  It is involved in a process called methylation along with folic acid and vitamin B6.  Methylation is involved in such things as protecting your DNA from damage (and thus cancer) and formation of neurotransmitters that keep your brain happy (like epinephrine / adrenaline).  It is also essential for red blood cell formation and making the myelin sheath that helps your nerves function properly.

Here’s the problem.  We need stomach acid and a compound produced in the stomach called intrinsic factor to absorb vitamn B12.  Thus, anytime we interfere with digestion, our ability to absorb vitamin B12 is affected:

  • Ulcer or reflux drugs like Nexium or Prilosec can affect your absorption.
  • Bariatric surgeries like the Roux-en-Y gastric bypass that remove /detach the portion of the stomach that produces intrinsic factor and stomach acid require lifelong vitamin B12 supplementation.
  • As we age, much like every other area of the body, some degree of wearing away of the lining of the stomach that produces stomach acid and intrinsic factor occurs.

I have been the speaker at events in the past where a senior insists that he or she makes “too much stomach acid” because her doctor told them so and that is why Nexium was prescribed.  Too much stomach acid just doesn’t occur as we age.  Quite the opposite (termed hypo- or achlorhydria).

So how do we check for B12 levels?  Most doctors seem to run a B12 blood test looking just at serum B12 levels.  Here’s the problem–you could absolutely avoid B12 for weeks and load up the day before your B12 blood test and the value would come out normal.  In other words, it really doesn’t give a good idea of how well vitamin B12 is working in your body because it is highly variable.

So basically, taking a B12 blood test is just short of worthless.

Just in case you don’t believe me, you can look at this particular study.  Here are the details:

  • Researchers gave 100 elderly participants 500 μg/d, 100 μg/d, and 10 μg/d of vitamin B12 (as cyanocobalamin-more on this later) with low vitamin B-12 levels (<250 pmol/L) for 8 weeks.
  • All participants saw increases in vitamin B-12 and serum holoTC.
  • However, even at the “high” dose 8% of participants still did not reach normal vitamin B12 levels.
  • More importantly, a lab test called methylmalonic acid, MMA was still low in 15–25% of people.

I’ve got a few comments.

First, most forms of vitamin B12 in supplements and injections (ALWAYS check this with injections!!) are of the cyanocobalamin form.  This is NOT the form the body uses.  Rather methylcobalamin or hydroxycobalamin are the preferred forms.  You can read more about this in a previous blog post that can be found by clicking here.

Next, the vitamin B12 blood test is not the best way to check for B12 status.  Checking what vitamin B12 DOES is far more important.  This can be done with the lab values mean corpuscluar volume (MCV), methylmalonic acid and homocysteine.  As seen in this study, the MMA was a much better marker for vitamin B12 status than was the B12 blood test.

Finally, dosage is important.  Our office uses a supplement that has 2,000 mcg of vitamin B12–4 times the dosage used in this study.  At the very least, 1,000 mcg dosage should be used in anyone with concerns over his or her vitamin B12 levels.

James Bogash

For more than a decade, Dr. Bogash has stayed current with the medical literature as it relates to physiology, disease prevention and disease management. He uses his knowledge to educate patients, the community and cyberspace on the best way to avoid and / or manage chronic diseases using lifestyle and targeted supplementation.