a hand picks up a vitamin pill that is only 25% full to imply a vitamin deficiency

Metformin and Vitamin B12 Deficiency

Metformin is one of the first-line medications and most commonly prescribed oral medication for managing type 2 diabetes. It is important to note that one possible side effect that many people do not know about is the increased risk of vitamin B12 deficiency with long-term use of Metformin. One study found that over 4.3 years, Metformin reduced vitamin B12 levels by 19%, while another study found a 20.3% prevalence of vitamin B12 deficiency after 9.5 years of Metformin use.1,2

What is vitamin B12?

Vitamin B12 is a water-soluble vitamin that is necessary for the development and function of brain and nerve function. Since 2017, The American Diabetes Association started recommending monitoring B12 levels in patients taking Metformin long-term.

What are common symptoms of vitamin B12 deficiency?

Since some symptoms of B12 deficiency are similar to diabetic neuropathy such as pain and tingling, it can often go unnoticed.

Common symptoms include:

  • Weakness or feeling tired
  • Heart palpitations or shortening of breath
  • Numb or tingling feeling in hands or feet
  • Nausea or changes in appetite

How much vitamin B12 is recommended for adults?

The Recommended Dietary Allowance (RDA) recommended amount of B12 for all adults (above the age of 14) is 2.4 mcg.; women who are pregnant or lactating have an increased need of vitamin B12, and the RDA ranges from 2.6 mcg during pregnancy and 2.8 mcg during lactation.

Where can I find vitamin B12?

We typically get vitamin B12 in our diet since it is found naturally in animal products. Good sources include: poultry, meat, fish, milk, and eggs. Vitamin B12 can also be added or fortified in foods such as cereals or plant-based milks. Below is a chart of top sources of B12 foods.

Top sources of B12 foods

FoodServing sizeMicrograms of B12 per serving
Clams3 oz84.1 mcg
Liver/beef3 oz70.7 mcg
Sockeye salmon3 oz4.8 mcg
Trout (rainbow trout)3 oz3.5 mcg
Tuna fish (canned in water)3 oz2.5 mcg
Milk (low fat)1 cup1.2 mcg
Yogurt (low fat)8 oz1.1 mcg
Swiss cheese1 oz0.9 mcg
Hardboiled egg1 egg0.6 mcg
Nutritional yeast1 tbsp5 mcg

Who is at risk?

  • Individuals who are vegans or follow a mostly vegetarian plant-based diet (since B12 is found in animal foods)
  • Individuals with certain gastrointestinal (GI) disorders such as Celiac or Crohn's disease
  • Individuals who take certain medications (Metformin or heartburn medicine)
  • Individuals who had gastrointestinal surgery such as weight loss surgery
  • Women who are pregnant or lactating

How is vitamin B12 checked?

Discuss with your doctor if you are at risk of vitamin B12 deficiency and could benefit from checking vitamin B12 levels. Vitamin B12 is usually checked through bloodwork.

How is vitamin B12 deficiency treated?

Eat more vitamin B12 foods! Follow the list above to choose a diet rich in B12. If vitamin B12 deficiency is present, you may benefit from taking a vitamin B12 supplement. **If you are considering taking a supplement discuss this with your doctor and health care team prior to starting.

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