Metformin is a popular oral diabetes drug taken by millions and used to help manage the growing burden of Type 2 diabetes. It works by lowering the amount of glucose made by the liver and by increasing cells sensitivity to insulin.

In recent years however, concerns have been raised over the increased risk of B12 deficiency in people who take metformin – with some estimates suggesting that between 10% - 30% of people who regularly take metformin have decreased B12 absorption. It’s not clear exactly how this happens, but it is likely that depletion occurs through the interruption of a calcium-dependent mechanism.

Why vitamin B12 is essential for your health…

Needed to make red blood cells - Vitamin B12 is needed for the manufacture of red blood cells; deficiency leads to a certain type of anaemia, which causes the body to produce abnormally large red blood cells that can’t function properly.

Nerve cell function - Vitamin B12 is important for the normal function of nerve cells, and to manufacture myelin, the insulating material that surrounds some of our nerve cells and helps to speed the transmission of messages from one nerve cell to another.

DNA replication - Vitamin B12 is required for the replication of DNA

Signs of vitamin B12 deficiency

 • Weakness, numbness, tingling, fatigue, dizziness, constipation, loss of appetite, irritability and swelling / irritation of the mouth and tongue

 • Megaloblastic anaemia

 • Impaired brain function – advanced B12 deficiency may even cause dementia severe enough to resemble Alzheimer’s disease – however this is corrected with supplementation

Who’s most at risk?

It’s likely that anyone taking metformin may be at a higher risk of vitamin B12 deficiency. Other groups are at increased risk too, and will need to be particularly careful when taking metformin. These include:

 • Older adults over 50 often have lower levels of stomach acid and may have trouble absorbing the vitamin B12 naturally present in food

 • People with pernicious anaemia, whose bodies do not make the intrinsic factor needed to absorb vitamin B12

 • Those who have had gastrointestinal surgery or who have digestive disorders such as coeliac or Crohn’s Disease. These conditions may decrease the amount of B12 the body can absorb

 • Those who are vegetarian & vegan, since only animal foods naturally contain vitamin B12

What can I do about it?

If you’re taking metformin and concerned about the risk of vitamin B12 deficiency, it’s best to speak to your GP and ask if they can monitor closely your blood levels of vitamin B12. It may be necessary to supplement vitamin B12 and sometimes folic acid too but it’s important to get this checked with your GP as a first port of call. 

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