Metformin is the most widely prescribed medication to treat diabetes (usually type 2 diabetes) in the world. Its effectiveness equals or exceeds many of the other oral medications available and has an excellent safety profile for most individuals. However, for the last ten to fifteen years there has been a question as to whether metformin causes B12 deficiency in those who take the drug for long periods of time.
Several studies and clinical cases have noted suboptimal blood levels of B12 in those who have taken metformin for extended periods. The National Nutrition and Health Examination reviewed the blood work on 1,621 people with diabetes, more than a third of whom were taking metformin, and demonstrated a reduction in serum B12 levels in people who took metformin compared to those who did not.
But just because these people taking metformin had lower levels of B12 in their bloodstream doesn’t necessarily mean the B12 that’s there isn’t getting the job done. New measurements of B12 activity have indicated that although metformin does seem to reduce blood levels of B12, this may not reduce the vitamin’s effectiveness in carrying out it its functions in the body. When B12 doesn’t work the way it’s supposed to, levels of something called total plasma homocysteine (tHcy) go up. But newer studies looking at the levels of tHcy in people who take metformin have found that they have not been elevated.
According to an article published this year in Diabetes Care, “low serum B12 alone without disturbances in the metabolic markers has no diagnostic value.” From a practical standpoint, this means that if a B12 deficiency is suspected from a serum B12 test, further testing should be undertaken before assuming the patient is B12 deficient.
B12 is one of the B-family of vitamins that is important for the healthy development of blood cells , DNA and the nervous system. Although it is known as a water soluble vitamin, we can store vitamin B12 in the liver for up to one year. B12 is widely distributed in the diets of those who eat any animal products; although those following a vegan diet will need to consume a B12 supplement or B12 enriched tofu or yeast to obtain adequate amounts of the vitamin.
B12 deficiency can lead to megaloblastic anemia, a type of anemia in which the red blood cells are significantly larger than normal. People with mild B12 deficiency may feel weak or tired, bleed easily, experience tingling in the hands and feet and swelling of the tongue. Severe B12 deficiency can have serious effects such as memory loss, delusions, loss of taste and smell.
Metformin contributes to serum B12 deficiency by preventing its transfer into the blood through a calcium dependent membrane, leading to decreased absorption. In addition, in order for B12 o be absorbed into the bloodstream it needs an acid environment in the stomach. Age and intake of acid reducing medications, such as anti-acids or proton pump inhibitors increase the likelihood that older adults may suffer from a B12 deficiency as can certain gastrointestinal disorder such as atrophic gastritis and Crohns disease or surgical reduction of the stomach.