What Happens if You Take Too Much Vitamin B12?

  • Medical Reviewer: Mahammad Juber, MD
Medically Reviewed on 10/4/2022

What does vitamin B12 do?

Vitamin B12 plays an essential role in many of your body's functions. If you take too much vitamin B12, you may suffer from nausea, vomiting, headache, diarrhea, tiredness or weakness, and tingling.
Vitamin B12 plays an essential role in many of your body's functions. If you take too much vitamin B12, you may suffer from nausea, vomiting, headache, diarrhea, tiredness or weakness, and tingling.

Vitamin B12 plays an essential role in many of your body's functions. Because vitamin B12 is important for maintaining your energy levels, some people promote taking high doses of vitamin B12, far beyond the recommended dose, to improve your health. Others say vitamin B12 is water-soluble, so your body just flushes out what it doesn't need. 

In this article, you'll find out if it's truly safe to take more vitamin B12 than you need and the benefits and risks of supplementing vitamin B12 levels. 

Vitamin B12 is also called cobalamin. It has the most complex and largest chemical structure of all vitamins, and it's the only one with a metal ion: cobalt. 

Your body absorbs vitamin B12 through your stomach, and from there, it travels to your blood and cells to help your body: 

Form healthy red blood cells

Vitamin B12 helps your body produce red blood cells and DNA. Your red blood cells deliver oxygen to the rest of your body, which helps your body produce the energy you need to be healthy. If your body doesn't get enough vitamin B12, your red blood cells become too large. This makes it hard for them to circulate in your blood and may cause anemia

Improve energy levels

If you're not getting enough vitamin B12, you may feel weak and tired. For people who are deficient in vitamin B12, getting enough can noticeably boost energy levels. This is probably where the idea that taking more vitamin B12 than you need will give you extra energy originally came from. However, there's no evidence that people with normal levels of vitamin B12 would get more energy by ingesting more B12. 

Maintain healthy brain function

Vitamin B12 is important for healthy brain function, especially as we get older. Low levels of vitamin B12 have been associated with dementia and cognitive decline. Still, it's not clear if taking vitamin B12 supplements will improve brain functioning in people with normal levels of vitamin B12.

Prevent vision loss

People with low levels of vitamin B12 are at a higher risk of developing age-related macular degeneration. This is a type of gradual vision loss that can happen in people over the age of 50. 

Prevent neural tube defects

Low vitamin B12 levels in mothers have been associated with neural tube defects in infants. Neural tube defects include conditions such as anencephaly and spina bifida, which are usually fatal birth defects that happen when the baby's neural tube doesn't properly close. 

How do you know if you're getting enough vitamin B12?

Your body doesn't naturally produce vitamin B12, so it's important to get it from your diet. Vitamin B12 is found in almost all animal food sources, including eggs, dairy products, meat, fish, and poultry. It's also added to many fortified foods such as breakfast cereals. If you don't eat animal products, nutritional yeast is also high in vitamin B12. 

Vitamin B12 deficiency isn't very common in the US, as people who don't eat enough animal products can still get vitamin B12 from supplements or fortified food sources. Older people and people with digestive tract conditions are most at-risk for developing vitamin B12 deficiencies. 

Vitamin B12 is absorbed through the digestive tract. Most cases of vitamin B12 actually happen because your body doesn't absorb enough, not because you aren't getting enough. 

Some conditions that can cause this vitamin B12 deficiency include: 

  • Atrophic gastritis, an inflammation of the stomach
  • Surgical removal of part of the stomach or intestines
  • Conditions that affect your intestine's ability to absorb nutrients, such as Celiac disease
  • Pancreatic insufficiency
  • Alcoholism
  • Acquired immune deficiency syndrome (AIDS)

Some people who don't have enough of a protein called the "intrinsic factor" also have a vitamin B12 deficiency. 

Some symptoms of vitamin B12 deficiency include:

You are more at-risk for developing vitamin B12 deficiency if you are: 

  • Pregnant
  • Over 65
  • Vegan
  • Take medicine for diabetes
  • Take medicine for heartburn
  • Have had surgery to remove part of your bowels

How much vitamin B12 do you need?

The amount of daily vitamin B12 you need depends on your age: 

  • Birth to 6 months: 0.4 mcg
  • 7 to 12 months: 0.5 mcg
  • 1 to 3 years: 0.9 mcg
  • 4 to 8 years: 1.2 mcg
  • 9 to 13 years: 1.8 mcg
  • 14 years or older: 2.6 mcg
  • Pregnant: 2.6 mcg
  • Lactating: 2.8 mcg 


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Can you take too much vitamin B12?

Because vitamin B12 is water-soluble, your body usually just absorbs what it needs and excretes the rest in your urine. No adverse or toxic events have been reported in healthy people who get too much B12 from food or supplements. 

However, if you are ill, high doses of vitamin B12 that you might receive to treat a deficiency may cause some symptoms such as: 

Additionally, if you're taking vitamin B12, some medicines can interfere with your ability to digest it, including

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Medically Reviewed on 10/4/2022

Cleveland Clinic: "Vitamin B12 Benefits and Best Sources."

Mayo Clinic: "Vitamin B-12."

National Institutes of Health: "Vitamin B12."

Oregon State University: "Vitamin B12."