What is Vitamin B12?

Vitamin B12, also known as cobalamin, plays a crucial role in many important functions in the body. It is essential for nervous system fuction, blood cell formation, metabolism of folic acid, and synthesis of DNA (1)In the diet vitamin B12 is typically obtained through consumption of meat or milk.  The best source of vitamin B12 can be found in clams and liver, with a 3 oz portion of clams providing 1400% of the Daily Value!(1,2).

The digestion and absorption of vitamin B12 relies on certain factors to be present in order to be successful. The high acidity of the stomach is an important part of the digestive process because it allows for proteins surrounding vitamin to break free, continuing digestion (2). Different transporters and chaperones are required for absorbtion by the cells. Because there are many steps in the process of digestion and absorption, there are many areas that can go wrong if not all that is required is present.  

Does Taking Metformin Increase Risk of Vitamin B12 Deficiency?

Metformin is the most commonly prescribed drug to individuals with type 2 diabetes and is also used for insulin resistant conditions like polycystic ovarian syndrome (PCOS) (4). Metformin has many benefits for those with insulin resistance, and is prescribed as a first line of treatment. However in a systematic review of multiple research studies, it was concluded that long term use of metformin had a significant impact on a reduction of vitamin B12 concentrations (3).  Studies show the prevelance of vitamin B12 deficiency to be has high as 30% in patients with type 2 diabetes taking metformin (5).

Groups At Risk For Vitamin B12 Deficiency

  • older adults
  • vegetarian or vegan diets
  • use of proton pump ihibitors (PPIs)
  • gastrointesntial disorders (Crohns diease and celiac disease)
  • history of gastrointenstial surgery

What Are The Risks Of Vitamin B12 Deficiency?

People with type 2 diabetes are at an increased risk for cardiovascular complications as well as peripheral neuropathy, and having low vitamin B12 levels increases this risk(2). Elevated cardiovascular disease risk is due to the role vitamin B12 plays in metabolism of an amino acid called homocysteine. Without B12, homocysteine levels stay elevated, which can increase your risk of heart disease (2,3). Peripheral neuropathy is a condition in which multiple symptoms can be present including pain, numbness, tingling in hands or feet, and sensory loss (7). With a vitamin B12 deficiency, damage can occur to myelin sheaths that surround nerves. The myelin sheaths protect nerves and without this protection, neuropathy can develop (7).

Bottom Line

If you are at increased risk for vitamin B12 deficiency you should talk to your doctor or dietitian about a supplement. According to the Institute of Medicine vitamin B12 is not known to cause any adverse side effects at high doses, meaning the risks of supplementing are likely low (6). Studies suggest supplements may be beneficial for certain groups but you will want to make sure you are taking the correct dose and from of the vitamin for the greatest result.  (2,3).