Metformin is one of the most commonly used medications to treat type 2 diabetes. It’s inexpensive, available in generic form and quite effective for lowering blood sugar levels. Some preliminary animal studies also show that taking metformin has additional benefits such as reducing the risk of certain types of cancer - and it may even prolong life. But there are side effects of metformin that many doctors don’t talk about with patients. Taking metformin can cause permanent nerve damage.
How does a drug like Metformin that has so many benefits cause such a severe side effect as nerve damage? Three out of 10 people who take metformin long-term develop a deficiency of vitamin B12. It can take 10 or 15 years to develop symptoms of B12 deficiency since the liver stores B12 - and it can take that long to deplete those stores.
B12 deficiency causes damage to nerves that may be irreversible. Unfortunately, B12 nerve damage may be mistaken for diabetic neuropathy - and may not be recognized as a metformin side-effect. Thus, it may go untreated and become permanent.
B12 neuropathy usually starts with numbness and tingling in the feet and hands, but this side effect gradually progresses to muscle weakness and balance problems. The symptoms closely mimic those of multiple sclerosis. If vitamin B12 deficiency goes untreated, a person with this deficiency can lose the ability to walk. Fortunately, replacing the lost vitamin B12 can reverse B12 nerve damage – but only if it’s caught early.
Vitamin B12 is normally absorbed in the portion of the small intestine called the ileum. To be adequately absorbed, it binds to a protein called intrinsic factor, which is required for it to be transported across the intestine and into the bloodstream. Metformin side effects include interference with the absorption of this vitamin B12-intrinsic factor complex, leading to a deficiency once liver stores of vitamin B12 are used up.
If you’re taking metformin, ask your doctor to check a vitamin B12 level through a blood test at least once a year. If your levels are low, you can get B12 injections monthly to bring them back up and reduce your risk of B12 neuropathy and nerve damage. Discuss this issue with your doctor before taking metformin – and ask your doctor to check a B12 level before you start taking it to serve as a baseline. Older people and vegetarians are at high risk for vitamin B12 deficiency too since vitamin B12 isn’t found in most plant foods. If you take metformin – take it safely to avoid side effects. Don’t risk permanent B12 nerve damage.