Key takeaways

  • If a person does not get enough vitamin B12, a doctor may suggest supplements containing more than the daily recommended dose. The body does not store excess vitamin B12, so taking extra is usually not harmful.
  • Vitamin B12 is a water-soluble vitamin, meaning the body excretes any excess through urine rather than storing it. Healthcare professionals have not identified any serious side effects from high-dose vitamin B12 supplementation.
  • Talk with a healthcare professional if there are concerns about vitamin B12 levels. They may recommend supplements and can advise on the dosage.

Vitamin B12 is vital for human life due to its role in making red blood cells and supporting the function of the brain and nerves.

There are no documented serious adverse effects from taking excess vitamin B12. However, it is best to follow guidelines from a healthcare professional.

The Office of Dietary Supplements (ODS) states that vitamin B12 has a low risk of toxicity. This is because the body does not retain excess amounts.

According to the ODS, the recommended dietary allowance (RDA) of vitamin B12 by age is as follows:

  • 0 to 6 months: 0.4 micrograms (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 and older: 2.4 mcg

During pregnancy, the RDA of vitamin B12 is 2.6 mcg. During lactation, the RDA is 2.8 mcg.

In general, taking higher-than-recommended levels of vitamin B12 is well tolerated. However, there are few reports of serious side effects.

A 2019 case report describes a case of a young woman who was treated for severe pernicious anemia with multiple daily doses of 1 milligram (mg) of cyanocobalamin, a synthetic form of B12. It resulted in acne, palpitations, anxiety, uncontrollable movements, facial redness, headache, and insomnia.

A 2023 case report describes extensive acne-like lesions all over the body as a reaction to vitamin B12.

Healthcare specialists divide vitamins into two categories: water-soluble and fat-soluble. Water-soluble vitamins dissolve in water and exit the body via the urine. Vitamin B12 is a water-soluble vitamin, and this is one reason why higher vitamin B12 levels are not known to be toxic.

However, while vitamin B12 appears to be generally safe, more is not necessarily better.

There is no need to take very high doses of vitamin B12. No data suggests that very high supplementation levels are any more effective at boosting a person’s immune system or bodily functions if they do not have a vitamin B12 deficiency.

A high vitamin B12 blood level is possible. This is known as hypercobalaminemia. It may lead to symptoms such as tingling, numbness, and muscle problems.

High vitamin B12 levels may also be present in people with conditions such as liver disease and certain cancers.

It is unclear exactly how much vitamin B12 a person would need to take to lead to hypercobalaminemia. There is currently no established tolerable upper limit.

A healthcare professional may recommend taking vitamin B12 supplements during pregnancy, particularly if a person is not getting enough vitamin B12 from their diet.

It is important to get enough vitamin B12 during pregnancy and when nursing, as a B12 deficiency may increase the risk of developmental problems.

Although there is currently no evidence to suggest any adverse side effects from excess vitamin B12 supplementation, there is no need to take excessively high amounts of the vitamin, as the body can only absorb so much anyway.

Hypercobalaminemia refers to high vitamin B12 levels in the blood. However, it is unlikely to develop if a person takes the recommended dosage of vitamin B12 supplements.

It is best to follow a healthcare professional’s guidance on whether they recommend vitamin B12 supplements based on individual circumstances.