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How much vitamin B12 is too much?

Dosage and potential risks of taking too much vitamin B12

Vitamin B12 plays many crucial roles in the body. Some think taking megadoses is best for their health. This article reviews how much vitamin B12 is too much.

This article is based on scientific evidence, written by experts, and fact-checked by experts.
We look at both sides of the argument and strive to be objective, unbiased, and honest.
How much vitamin B12 is too much?
Last updated on June 18, 2023, and last reviewed by an expert on June 28, 2022.

Vitamin B12 is a water-soluble nutrient that plays many critical roles in your body.

How much vitamin B12 is too much?

Some people think that taking high doses of B12 — rather than the recommended intake — is best for their health.

This practice has led many to wonder how much of this vitamin is too much.

This article examines the health benefits, as well as potential risks of taking megadoses of B12.

In this article

Benefits of supplementing with vitamin B12

There’s no question that vitamin B12 is essential for health.

It’s responsible for numerous functions in your body, including red blood cell formation, energy production, DNA formation, and nerve maintenance.

Though B12 is found in many foods, such as meat, poultry, seafood, eggs, dairy products, and fortified cereals, many people don’t get enough of this important vitamin.

Health conditions such as inflammatory bowel disease (IBD), certain medications, genetic mutations, age, and dietary restrictions can all contribute to an increased need for B12.

Vitamin B12 deficiency can lead to serious complications such as nerve damage, anemia, and fatigue, which is why those at risk should talk with their doctor about adding a high-quality B12 supplement to their diet.

While people who consume adequate amounts of B12-rich foods and can properly absorb and use this nutrient don’t necessarily need to supplement, taking extra B12 has been linked to some health benefits.

For example, studies show that supplemental B12 may benefit people without a deficiency in the following ways:

Although B12 supplements are commonly taken to boost energy levels, there is currently no evidence suggesting that more B12 increases energy in people with adequate levels of this vitamin.

However, B12 supplements will most likely increase energy levels in those who are deficient, as this nutrient plays an important role in converting food into energy.

Vitamin B12 dosage: How much should you take per day?
Suggested read: Vitamin B12 dosage: How much should you take per day?

Summary: B12 is an important nutrient that is essential for red blood cell formation, DNA synthesis, and many other vital processes. Supplements may help boost mood and reduce symptoms of depression in those who are not deficient in this vitamin.

Is taking high doses of B12 helpful or harmful?

Since B12 is a water-soluble vitamin, it’s generally considered safe, even at high doses.

No tolerable upper intake level has been established for B12, due to its low level of toxicity. The upper intake level refers to the maximum daily dose of a vitamin unlikely to cause adverse side effects in the general population.

This threshold has not been set for B12 because your body excretes whatever it doesn’t use through your urine.

However, supplementing with excessively high levels of B12 has been linked to some negative side effects.

Several studies have shown that megadoses of the vitamin can lead to outbreaks of acne and rosacea, a skin condition that causes redness and pus-filled bumps on the face.

Yet, it should be noted that most of these studies focused on high-dose injections rather than oral supplements.

There is also some evidence suggesting that high doses of B12 may lead to negative health outcomes in those with diabetes or kidney disease.

One 2010 study found that people with diabetic nephropathy (loss of kidney function due to diabetes) experienced a more rapid decline in kidney function when supplemented with high-dose B vitamins, including 1 mg per day of B12.

Suggested read: B-complex vitamins: Benefits, side effects and dosage

What’s more, the participants receiving the high dose of B vitamins had a greater risk of heart attack, stroke, and death, compared to those receiving a placebo. However, more recent studies are needed to support this claim.

Another study in pregnant women showed that extremely high B12 levels due to vitamin supplements increased the risk of autism spectrum disorder in their unborn child.

Though there is evidence that supplementing with B12 may cause negative health outcomes, studies have demonstrated that daily oral supplements of up to 2 mg (2,000 mcg) are safe and effective in treating B12 deficiency.

For reference, the recommended daily intake of vitamin B12 is 2.4 mcg for both men and women, though pregnant and breastfeeding women have a higher need.

Summary: Although there is some evidence that very high doses of B12 may cause adverse health effects in certain populations, megadoses of this vitamin are commonly used to safely and effectively treat B12 deficiency.

How much B12 should you take?

For healthy individuals who are not at risk for B12 deficiency, eating a well-rounded, nutrient-rich diet should provide all the B12 their body needs.

Food sources of this vitamin include eggs, red meat, poultry, seafood, milk, yogurt, fortified cereals, nutritional yeast, and fortified non-dairy milk.

However, individuals taking medications that affect B12 absorption, pregnant or breastfeeding women, vegans, and anyone with a condition that negatively impacts the absorption of or increases the need for B12 should consider talking with their doctor about taking a supplement.

Additionally, evidence from population studies suggests that B12 deficiency in older adults is common, which is why it’s recommended that adults over 50 years old consider taking supplements.

While megadoses of up to 2,000 mcg are considered safe in treating B12 deficiency, it’s always best to avoid excessive amounts of any vitamin, especially when it’s not needed.

Suggested read: Zinc: Benefits, deficiency, food sources and side effects

Though daily high doses of B12 are unlikely to cause harm in most people, extremely high doses should be avoided unless a healthcare professional prescribes it.

If you think you may be deficient in B12, speak with your doctor, who can recommend an appropriate treatment based on your level of deficiency.

While no upper intake level has been set for B12, your body’s ability to absorb the vitamin depends on how much it needs.

For example, it’s estimated that only 10 mcg of a 500-mcg B12 supplement is absorbed in people without a deficiency.

For this reason, taking high doses of B12 does not benefit people without an increased need.

Summary: Although supplemental B12 is required for people with an increased need for this vitamin, it’s unnecessary for those without a deficiency to take high doses.


B12 is an important nutrient that is popularly used as a nutritional supplement, even by those without a B12 deficiency.

Though doses of up to 2,000 mcg of vitamin B12 are considered safe, it’s best to speak with a doctor to find out whether taking a supplement is necessary.

Most people can fulfill their B12 needs through a nutrient-rich diet. However, some people, including older adults and those with certain dietary restrictions, should consider talking with their doctor about supplementation.

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