Metformin and vitamin b12: What you should know.

In this article:

• How does metformin affect vitamin B12 levels?
• How do I know if my B12 levels are too low?
• Should I take B12 while on metformin?
• Foods and supplements high in vitamin B12

In this article

• How does metformin affect vitamin B12 levels?
• How do I know if my B12 levels are too low?
• Should I take B12 while on metformin?
• Foods and supplements high in vitamin B12

Metformin, an anti-diabetic medication, is a popular prescription drug to help manage blood glucose levels for those with diabetes mellitus. However, a common risk factor of taking metformin is low vitamin B12 levels, which can cause fatigue, mood changes, changes in cognitive function, and more.

If the use of metformin is affecting your vitamin B12 levels, a supplement and diet changes may help. Learn everything the experts have to say about taking a vitamin B12 supplement when on metformin.

How does metformin affect vitamin B12 levels?

Before understanding how metformin can affect a person’s vitamin B12 levels, it’s helpful to better understand how the commonly prescribed drug and vitamin B actually work.

Metformin is an antidiabetic prescription drug that belongs to a class of medications called biguanides. It helps regulate blood sugar levels for those with Type 2 diabetes or gestational diabetes by increasing insulin sensitivity, decreasing glucose production by the liver, and decreasing glucose absorption from the intestines. Metformin treatment is also sometimes used for those who experience insulin resistance.

Vitamin B12, also known as cobalamin, is one of the B vitamins under the umbrella of the vitamin B complex, which includes eight different types of vitamin B. This essential nutrient has many important functions in our body, including DNA synthesis, nerve function, red blood cell production, and metabolism. It is commonly found in foods of animal origin, like meats, fish, dairy, and eggs. A deficiency in vitamin B12 can cause a wide range of side effects, from mood changes to anemia to heart palpitations.

How exactly can metformin affect vitamin B12 serum levels?

“Metformin reduces vitamin B12 absorption in the gastrointestinal tract,” explained Dr. Farhan Malik, MD, Owner and Senior Medical Director at Prometheus by Dr. Malik. He further added, “The reduction in B12 absorption is thought to be due to metformin altering gut mobility and intestinal cell membrane function.”

The gut is a sensitive system and it’s easy for the absorption of vitamin B to be compromised — even for those not taking metformin.

“The B12 absorption pathway is a very complex pathway and can be disrupted in many different ways, including stomach acidity, taking certain antacids, or even having inflammation in the gut,” said Dr. Sulagna Misra, an internal and integrative medicine physician and owner of Mirsa Wellness. 

Metformin does not affect B12 levels instantly. It can take months and years for diabetic patients on the drug to begin noticing symptoms of a B12 deficiency. Short-term metformin users are at less risk of developing a deficiency, while long-term use of metformin therapy can increase the risk of vitamin B12 deficiency.

How do I know if my B12 levels are too low?

Initially, symptoms of a low vitamin B12 level can be subtle, perhaps you’ll start experiencing general fatigue, dizziness, or weakness. Over time, these symptoms will get worse as the deficiency continues. 

If you suspect your B12 levels are off, your primary healthcare provider can take blood samples to determine if your levels are normal or deficient. A B12 level above 300 picograms per milliliter (pg/mL) will be interpreted as normal. Borderline deficient levels between 200 and 300 pg/mL may need further testing. Providers may order a blood test called methylmalonic acid level, which can show early B12 deficiency before it shows up on standard testing. If blood testing finds levels under 200 pg/ML, these patients are considered deficient in B12.

There are several symptoms associated with a vitamin B12 deficiency, which we’ve listed below.

Vitamin B12 deficiency symptoms when taking metformin

• Peripheral neuropathy (which can feel like pain, tingling, or pins and needles)
• Headaches
• Nerve damage
• Visual changes
• Changes to the tongue
• Macrocytic anemia (which means red blood cells cannot be properly formed)
• Fatigue or exhaustion
• Shortness of breath
• Rapid heart rate
• Jaundice or yellowing of the skin
• Difficulties sleeping
• Depression
• Cognitive impairment such as slowed thinking, brain fog and memory problems
• Psychosis
• Small intestine bacterial overgrowth

Should I take B12 while on metformin?

If your B12 levels are low from metformin or were low before starting the antidiabetic drug, a vitamin B12 supplement can be beneficial. However, not everyone on metformin needs a B12 supplement because not all users will have a deficiency. There are groups of metformin users at higher risk of a deficiency.

Metformin users who have a longer treatment duration of the drug may be at a higher prevalence of vitamin B deficiency while taking metformin. The dose of metformin may also play a role in vitamin B12 deficiency according to the latest research. The results of a recent study found that higher metformin doses (more than 1500 mg daily), “played an important role in metformin‐associated vitamin B12 deficiency while not contributing to the risk of peripheral neuropathy.”

Another group at high risk of lower B12 levels are those on a vegetarian diet or vegan diet, as B12 naturally occurs in animal-derived products. Pregnant individuals and older populations are another group at increased risk of low vitamin B levels.

Vitamin B12 supplementation may also be beneficial for those with diabetic neuropathy. A meta-analysis in 2022, examining previous studies, found that “vitamin B12 can improve neuropathic symptoms and reduce pain in patients with diabetic neuropathy.”

If your vitamin B12 levels are too low, there are a few ways to increase your intake of the vital nutrient. A diet rich in B12 can help increase these levels, but another option is vitamin B12 supplements.

“The recommended daily intake for adults is 2.4 mcg,” said Dr. Malik about B12 supplements. “Supplement doses range from 25-100 mcg for improved absorption.”

Depending on your preferred method of taking supplements, there are a few options.

“Sublingual tablets, nasal sprays, and injections can be effective for those with absorption issues,” explained Dr. Malik. ”Regular bloodwork is important to monitor levels over time. Consulting with a doctor can ensure proper supplementation based on individual health factors.”

When metformin-treated patients begin supplementing with vitamin B12 to decrease the adverse effects of a deficiency, it’s important to inform your doctor and first seek their medical advice. Healthcare professionals will want to continue with periodic monitoring to review if your metformin-induced vitamin B deficiency is improving.

“I’d also like to note that folic acid plays a part in some of this and it is very important to have your physician involved in B12 supplementation and figuring out why the B12 is low in the first place,” said Dr. Misra. ”Correcting the wrong vitamin or nutrient will not fix symptoms and may actually make them worse!”

Those with low B12 levels should take the supplement daily to help decrease the likelihood of health issues as a result of the vitamin deficiency.

Foods and supplements high in vitamin B12

“B12 is found in abundance in animal products so patients who are vegan or vegetarian are recommended to take supplementation,” explained Dr. Misra. She added, “Low levels are also found in people that drink a lot of alcohol or have a very nutritionally poor diet.”

While a standard B12 vitamin on the shelves of your local pharmacy may serve your purposes, we’ve also rounded up foods to add to your diet with naturally occurring B12 to help increase your intake.

Foods high in vitamin B12

The foods below have a naturally high level of vitamin B12 to help supplement your diet.

• Organ meats, like liver and kidneys, are high in B12. Lamb liver and kidneys are one of the highest sources of B12.
• Fish including tuna, salmon, and trout all have high amounts of vitamin B12.
• Sardines, which can be purchased in a can at your local grocery store, are nutritious and rich in B12.
• Clams are a good source of protein and have a high concentration of B12.
• Eggs have high levels of B12, especially the yolk compared to the egg whites. However, some studies have found that the body absorbs this source of B12 poorly compared to other foods.
• Dairy, including milk, yogurt, and cheese all have a decent amount of vitamin B12. Bovine milk can vary in B12 levels based on what the cows are fed.
• Fortified breakfast cereals are a great source of B12 for those who need to up their intake.