Metformin is often the first-line medication given to people diagnosed with Type 2 diabetes. Though it does a very good job getting blood sugar under control, it can also put you at risk for a vitamin B12 deficiency.
The B12-Metformin Connection
As one of the eight B-complex vitamins, B12 (cobalamin) is found naturally in fish, milk, yogurt, cheese, poultry, lean red meat and fortified foods, according to the Academy of Nutrition and Dietetics. It's an essential vitamin, needed to produce healthy red blood cells, among its other important jobs.
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As for metformin, part of a class of drugs called biguanides, it's a pill that helps lower your blood sugar by reducing the amount of glucose produced by your liver and helping your body respond better to the insulin made in your pancreas, according to the American Diabetes Association (ADA).
In addition to lifestyle changes — including eating a healthy diet, exercising regularly and maintaining a normal weight — people with diabetes may need medication, like metformin, to help their body use insulin more efficiently and stave off long-term damage from diabetes, the ADA says.
But there's a caveat. "Metformin decreases vitamin B12 absorption from the gut," explains Audrey Koltun, RDN, CDE, a certified diabetes educator and dietitian in the division of pediatric endocrinology at Cohen Children's Medical Center in Lake Success, New York.
Read more: B-Vitamin Complex Benefits and Side Effects
Are You at Risk?
B vitamins are water-soluble, which means they leave the body through urine. People with diabetes tend to urinate more frequently, which may put them at a higher risk for deficiency, even when they consume enough, warns the Diabetes Action Research and Education Foundation.
Some people may be more likely to lack B12 than others, independent of their diabetes status. "People who are strict vegetarians or vegans or those who have had weight-loss surgery are at high risk of B12 deficiency," Koltun says.
Symptoms of a deficiency may include fatigue or weakness, changes in balance and coordination and the feeling of pins and needles in your limbs, which is also a symptom of diabetic nerve damage, Koltun says. Because of its role in making red blood cells, a lack of B12 can also lead to anemia, according to the National Library of Medicine.
Ajaykumar D. Rao, MD, an associate professor of medicine at the Lewis Katz School of Medicine at Temple University and at the Center for Metabolic Disease Research at Temple University Hospital in Philadelphia, routinely tests B12 blood levels in his patients who take metformin. The good news is the remedy is straightforward.
"B12 deficiency is easily treated with B12 replacement in the form of a pill," Dr. Rao says, adding that everyone on metformin should talk to their doctor about getting the blood test and about taking vitamin B12 supplements based on the results.
More About B Vitamins
B12 is part of the B-complex, along with B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin) and B9 (folate, or folic acid). Of particular note for people with diabetes, vitamin B6 helps to produce insulin, according to the Academy of Nutrition and Dietetics.
However, Koltun warns that excess B6 can lead to nerve damage or neuropathy, already a risk from uncontrolled diabetes. Also, too much vitamin B3 can cause elevated blood sugar, another serious situation for people with diabetes.
High levels of supplemental biotin can interfere with certain lab tests. For instance, it can mask troponin, which helps doctors diagnose heart attacks, according to the Food and Drug Administration. Heart disease is the No. 1 cause of death for people with diabetes, so this is an important consideration, Dr. Rao says. "Be careful about biotin and always tell your doctor if you are taking supplements of this B vitamin," he says.
Work with your doctor or a certified diabetes educator to come up with a healthy diet that delivers getting the correct amounts of all the B vitamins for you. "One that's low in refined carbohydrates and sugars, and high in fiber, healthy fats (nuts, seeds, fatty fish), vegetables and fruits is good for diabetes," says Koltun.
- Academy of Nutrition and Dietetics: “What Are B-Vitamins?”
- American Diabetes Association: “Blood Sugar and Insulin at Work"
- Audrey Koltun, RDN, CDE, CDN, registered dietitian nutritionist, certified diabetes educator, division of pediatric endocrinology, Cohen Children’s Medical Center, Lake Success, New York
- Ajaykumar D. Rao, MD, associate professor, Lewis Katz School of Medicine at Temple University and Center for Metabolic Disease Research at Temple University Hospital, Philadelphia
- Food and Drug Administration: “The FDA Warns that Biotin May Interfere with Lab Tests”
- National Library of Medicine: “B Vitamins”
- Diabetes Action Research and Education Foundation: “B Vitamins in Diabetes: Just Expensive Urine”