Endocrine Today current issue presents the case for routine screening for B12 levels for patients on metformin therapy. I was pleased to see this finally being discussed openly as I have always included the fact that metformin can cause B12 deficiency in my patient and professional lectures. Since I thoroughly read full prescribing info about all diabetes medications, I knew it clearly states that precaution for metformin. I have found, however, that nobody seems aware of that potential problem. 

Endocrine Today discusses the case for neuronal damage caused by B12 as presented by David S H Bell,MD in a case reported in Southern Medical. He states that Vitamin B12 deficiency is a chronic complication of metformin therapy that can cause irreversible neuronal damage. Metformin has been around since 1955. It is widely used because it is inexpensive, readily accepted by patients and seems to assist in weight loss in some patients.

Another concern that I have with metformin is the precaution about lactic acidosis. This  is also stated in the medication literature, but lactic acidosis is not widely reported. I often wonder if subclinical lactic acidosis is present in people on metformin. That would only be identified by labs. Sufficient hydration, I feel, needs to be stressed in people on metformin to assure that the kidneys get all the help they need to get rid of the lactic acid by product of anaerobic metabolism caused by metformin.

Metformin is widely used for pregnancy (off label, but used) and for children. Patients on metformin need to be instructed regarding precautions with metformin...including alcohol consumption.

Great post!
I discuss Vit B12 def. and metformin intake with all those who are on this drug and order Vit 12 test PRN.

Yes, I do discuss B12 and metformin with patients. I do the same with physicians as it seems not to be a widely recognized issue.

I discuss it as well. I learned the hard way, my dad was taking metformin and developed a B12 deficiency.  Now I know to tell patients about it!

I don't routinely discuss B12, so I'm glad you started this discussion. Is there a specific test you recommend to monitor B12 levels? If you find levels are low, do you recommend a specific type and amount of B12 supplement, or will focusing more on food sources of B12 work?

Finally, could you explain the reason why metformin may lower B12 levels? I think that will help me understand this whole issue better. Thanks!

Hi Lynn,  it has to do with the mechanism of the gut.  Here is an article I found on it, with case studies:

http://ageing.oxfordjournals.org/cgi/content/full/35/2/200

I discuss it and then have ALL my patients on Metformin get a B12 shot (methylcobalamin) each month.  Serum B12 is a very poor analysis of B12--MMA is best--but the injection is inexpensive and a good prevention.

Calcium has been shown to help reverse the absorption problem that Metformin creates for B12, although I'm not sure of the exact physiology of how calcium works. 

Also, watch folic acid levels via homocysteine, as well.

Dr. Morstein

Agree with Dr Morstein-B12 injections Q mo(usually) work the best. The endocrinologists  in our practice prescribe Vitamin B 12 1000 mcg 1 t PO QD for those whose Vit B12 levels are seriously depleted. For some reason sublingual preparations don't work as well. Thanks. Isabella, RN/CDE.

The Endocrinologists are well aware of B12 deficiency with use of metformin. Usually B12 deficiency happen about 5 years of use of metformin. I agree with Dr David Bell ,that B12 levels should be checked periodically in patient taking metformin.Since one can ,T predict when it will happan,when I start patient on metformin,i tell them to take a tablet of B100. It has B12,and that will prevent B12 deficiency.
Lactic Acidosis is rare with metformin,Ther is a risk if GFR<35ml/min,or patient become dehydrated.So,good hydration,and F/U of GFR,and creatinin is important.Also if creatinin >1.5 in man,and .1.4 in woman it is recommended to D/C metformin.

How often should B12 levels be checked in patients on metformin?  Should these levels be checked more fquently, once someone has been on metformin for more than 5 years?

TwiceB12 to be cheked twice yearly,.If patient on B12 supplement once yearly .

Thanks for the answer, Dr. Sachmechi.

Donna Jornsay