What You Should Know About Metformin and Vitamin B12

People who take metformin to treat insulin resistance caused by type 2 diabetes or polycystic ovary syndrome (PCOS) may be at risk of developing a vitamin B12 deficiency, research has shown. Low levels of vitamin B12 can cause serious and sometimes permanent neurological damage, and so it's vital that levels of this nutrient be monitored in anyone who takes metformin (which is available as a generic product as well as under the brand names Glucophage, Glucophage XR, Glumetza, Fortamet, and Riomet).

If you're on this drug, and particularly if you've been taking it for a while, it's important to be aware of the association between long-term use of metformin and vitamin B12 deficiency. This will allow you to have informed discussions about your treatment with your doctor and empower you to play a vital role in your care.

Vitamin B12 is a water-soluble vitamin that's essential for nerve conduction, mental functioning, DNA synthesis, and red blood cell formation. It's readily available in animal products, including fish, meat, poultry, eggs, and milk and other dairy foods. The recommended daily amount of vitamin B12 for most adults is 2.4 micrograms (mcg).

A deficiency of vitamin B12 can affect mood and energy and even result in permanent and irreversible neuropathy (nerve damage). Symptoms of B12 deficiency include certain types of anemia, neuropathy, chronic fatigue, memory loss, confusion, mood changes, and eventually, even dementia.

A number of studies have found an association between long-term use of metformin and depleted vitamin B12 levels. Among the most significant of these, for example, was a secondary analysis from the Diabetes Prevention Program (DPP)/DDP Outcomes Study (DDPOS), one of the largest and lengthiest studies of metformin use ever conducted.

Published in the April of 2016 issue of the Journal of Clinical Endocrinology and Metabolism, it found that more than a thousand subjects who took metformin for around 12 years had a 13% increased risk of vitamin B12 deficiency for each year of total metformin use.

Another study found that people with type 2 diabetes who took metformin at doses of more than 1,000 milligrams (mg) for four or more years were especially at risk of vitamin B12 deficiency.

If you take metformin, a yearly check of your vitamin B12 status can alert your doctor to any dips in your levels that may be early signs of a deficiency. One way to determine vitamin B12 status is with a test that directly measures levels of B12 in a blood sample. A more sensitive test looking at levels of a metabolite in the blood called methylmalonic acid (MMA) may be able to detect low B12 levels earlier.

Meanwhile, including plenty of foods rich in vitamin B12 in your diet and/or taking supplemental B12 may help to prevent a deficiency. The methylcobalamin type of vitamin B12 in a sublingual form (under the tongue) is best absorbed by the body, but you should consult your doctor about the best supplement and correct dosage for you.