How Much Vitamin B12 is Too Much?

Vitamin B12 plays many important roles in the human body, including the formation of red blood cells and the normal function of the central nervous system. Vitamin B12 is found in animal foods, and most people get adequate amounts from the foods they eat. Supplementation is usually unnecessary for the average person. Let's explore the uses and benefits and if there's such thing as too much vitamin B12.

Key takeaways:

What is vitamin B12?

Vitamin B12 is a water-soluble nutrient with many functions in the human body. It helps prevent anemia, keeps nerve and blood cells healthy, and is involved in forming our genes. Vitamin B12 is found naturally in various animal foods, like eggs, milk, and meat. Food manufacturers fortify cereals and other foods with vitamin B12. It is necessary for survival, but heavy-dose vitamin supplementation is unnecessary for most people.

Vitamin B12 benefits

Studies on vitamin B12 and human health continue, but we know that vitamin B12 is essential for human health. The creation of healthy red blood cells requires vitamin B12. Without enough of it, red blood cells are formed irregularly. Their odd size and shape cause problems as they move through the blood, resulting in megaloblastic anemia. This results in symptoms like fatigue because the malformed red blood cells cannot carry enough oxygen to all the body tissues.

The essential functions of B12 are numerous:

  • Nervous system. It is required for the healthy function of the central nervous system;
  • Enzymes. It’s used in the production of several enzymes and normal cell production;
  • DNA. Vitamin B12 plays an important role in the production of DNA, the molecule inside every cell that carries all genetic information. Without vitamin B12, humans wouldn’t be able to grow and function.

Vitamin B12 is often viewed as a supplement that can help improve symptoms of depression or brain fog, but there is no evidence for that. In 2021, a group of researchers at the University of Zurich looked at over a dozen studies involving thousands of participants and found that vitamin B12 supplementation did not affect depression or cognitive function.

How much B12 do you need?

The Food and Nutrition Board of the National Academies of Sciences, Engineering, and Medicine sets the recommended intake amounts for vitamins and minerals. Your need for vitamin B12 increase as you age. Pregnant or breastfeeding women have higher requirements to provide enough for the growing fetus.

The recommended daily amount for the average adult is 2.4 mcg of vitamin B12. This amount can be consumed just by including three ounces of fish, meat, or poultry daily. The foods with the highest amount of naturally occurring vitamin B12 are beef liver and clams.

The majority of Americans who eat meat get enough vitamin B12 from foods. People who follow a vegetarian or vegan lifestyle will need supplementation since plant foods do not contain any vitamin B12. People with certain conditions may have trouble absorbing enough of the vitamin. They may need to speak with their doctor about supplementation.

People at risk of vitamin B12 deficiency include:

  • Older adults. They often have lower amounts of stomach acid needed to break down the vitamin into a usable form.
  • People with stomach issues. People with stomach disorders, such as atrophic gastritis, have an imbalance of stomach acid and the protein called intrinsic factor in their stomachs.
  • People with pernicious anemia. They lack the intrinsic protein factor needed to absorb B12 from food and supplements.
  • People with gastrointestinal tract disorders. Absorption issues are seen in people with Crohn’s disease, celiac disease, and intestinal or stomach surgery.
  • People who eat plant-based diets. People who eat little or no animal foods are at risk of B12 deficiency, especially vegans and vegetarians.
  • Some breastfeeding babies. The babies of vegans or vegetarians who are breastfed will need supplementation. No vitamin B12 will be available in the breast milk for the infant.

Vitamin B12 deficiency symptoms

Your body stores 2,000 times more vitamin B12 than you get from your diet each day, so deficiency is rare and can take years to develop. The typical signs of vitamin B12 deficiency include:

  • Fatigue
  • Weakness
  • Pale skin
  • Heart palpitations
  • Weight loss
  • Appetite loss
  • Numbness or tingling sensation in hands or feet
  • Depression
  • Infertility
  • Balance issues

Many of these overlap with iron-deficient anemia symptoms — vitamin B-12 and iron are both needed for healthy red blood cells. The most important sign of vitamin B12 deficiency in babies is failure to thrive, meaning the infant does not reach typical developmental milestones.

Evidence has shown more vitamin B12 deficiency in people taking the popular diabetes medication metformin for years. Vitamin B12 may be difficult to absorb for people with diabetes and could worsen nerve damage in neuropathy patients. Metformin is a safe and effective drug that helps people with diabetes be more sensitive to insulin. If you take metformin for diabetes, continue to take your medication and speak with your healthcare provider about your vitamin B12 levels.

Can you get too much B12?

Vitamin B12 is considered to have very low toxicity, so no 'Tolerable Upper Intake Level' (TUL) has been established. This means that the maximum daily intake levels of the vitamin are considered safe for the average person.

Your body will excrete any excess vitamin B12 through your urine, so it isn’t easy to take too much. Some people have taken mega doses of the vitamin, which can cause adverse health effects.

A specific form of acne, drug-induced acne, has been reported with mega-doses of B12 and other vitamins. There is mounting evidence that very high doses of vitamin B12 may lead to other negative health risks, like a higher risk of cancer. Another study found that high doses of vitamin B12 worsened outcomes for people experiencing diabetes-related loss of kidney function.

Vitamin B12 is important for good health. Without it, your body cannot function well, and problems like fatigue, depression, pale skin, and numbness may alert you to a problem. Vegetarians, vegans, and those with certain conditions may need to supplement with vitamin B12 for good health.



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