High Vitamin B12 Levels: What Are Its Side Effects?


Vitamin B12 is a nutrient essential for humans. It is good for your health as it helps DNA synthesis and metabolic pathways. You can consume vitamin B12 through your diet. If you follow a vegetarian diet, B12 tablets are required to avoid deficiency.

Why Is It Used?

Vitamin B12 has uses in:

  • Replenishing Vitamin B12 deficiency, which can occur due to:
  • Low absorption as a result of the loss of gastric intrinsic factor (IF)
  • Age-related decline in stomach acid production or prolonged use of certain medications, such as people undergoing antacid therapy (acid exposure releases protein-bound vitamins, so any impairment of gastrointestinal function leads to a reduced amount of vitamin B12)
  • Deficiency due to dietary reasons
  • Preventing canker sores, fatigue, cataracts, and fatigue
  • Vitamin B12 is critical for proper brain and spinal cord development, DNA synthesis, and the formation of red blood cells
  • Ensure a healthy pregnancy, as mothers with extremely low levels of vitamin B12 were found to be 3-5 times more likely to give birth to babies with congenital defects
  • Vitamin B12 helps regulate serotonin and energy production, impacting mood, sleep, and energy levels
  • Vitamin B12 keeps the brain healthy by preventing the loss of neuron function, and has been found to slow mental decline in early-stage dementia patients
  • Reducing the risk of macular degeneration, as adequate vitamin B12 reduces the levels of homocysteine (an amino acid associated with age-related decline in eye health)
  • High levels of homocysteine (an amino acid), which can be regulated by vitamin B12, in the blood is linked with heart conditions.
  • Supporting bone health, improving bone density, and decreasing the risk of osteoporosis
  • Ensuring healthy nails, hair, and skin

Recommended Dietary Allowance (RDA) refers to the average daily intake level that meets the nutrient requirements of most (97%–98%) healthy individuals.

The table below mentions the dietary recommendations for vitamin B12 (mcg: micrograms):




1-3 years

0.9 mcg

0.9 mcg

9-13 years

1.8 mcg

1.8 mcg

14-18 years

2.4 mcg

2.4 mcg

19+ years

2.4 mcg

2.4 mcg

During pregnancy

2.6 mcg

While breastfeeding

2.9 mcg

Foods rich in Vitamin B12

Vit B12 is naturally found in meats or foods from animal sources, including clams, liver, fish, poultry, eggs, and dairy products. The table below shows select foods rich in Vitamin B12


mcg per serving

% of Daily Value (as prescribed by the US FDA)

Cooked Clams (80-100g)



Cooked Atlantic Salmon (80-100g)



Light canned Tuna (80-100g)



Milk (1 cup, 2% fat)



Fat-free Yogurt (170-180g)



Cheddar Cheese (40-50g)



1 whole egg, cooked



1 medium Banana



Excessive Vitamin B12: Side Effects

The Food and Nutrition Board under the US Institute of Medicine states there is no maximum limit for vitamin B12 consumption because of its low toxicity levels. The body does not store excess amounts and excretes whatever it does not use, and thus, even at large doses, vitamin B12 is generally safe. However, some negative effects are associated with excessive vitamin B12:

  • A study in 2010 investigating the effect of drug-related acne showed that vitamin B12 exacerbated acne outbreaks.
  • Another study in 2020 investigated the effects of high-dose (>1mg) vitamin B12 injections (not oral supplements) for pernicious anemia treatment. The study also observed acne outbreaks, rosacea (reddened facial skin and rash), palpitations, and headaches in test subjects.
  • In addition to acne breakouts, vitamin B12 injection side effects include cause vein thrombosis, which heightens the risk of blood clots. In rare cases, polycythemia vera, a rare and slow-growing blood cancer, has been recorded.
  • Vitamin B12 has been used to treat high homocysteine plasma levels. A controlled trial with vitamin B12 tablets (1mg) and matching placebos was conducted.
  • Researchers have studied vitamin B12 supplement side effects for pregnant women. They found that unborn babies were more likely to develop autism spectrum disorder if their mothers had excessively high vitamin B12 levels.
  • High vitamin B12 can also cause fatigue, headache, nausea, and mood swings.


Human beings need vitamin B12 to survive. While the side effects of vitamin B12 tablets and food items are minimal, excessive levels of it can be harmful to your health, causing rashes, digestive problems, fatigue, and weakness. To avoid these, track and regulate your vitamin B12 consumption.


Why do we need vitamin B12?

Vitamin B12 is required to form DNA and red blood cells. It aids the development of brain and nerve cells as well.

How can I consume vitamin B12?

The following foods contain vitamin B12:

  • Meat
  • Eggs
  • Liver and kidney
  • Sardine, salmon, and trout
  • Fortified breakfast cereal

In case of excessive vitamin B12, how can I reduce its levels?

Specific measures like drinking more water, stopping B12 supplements, and avoiding foods rich in vitamin B12, can temporarily help decrease its levels in the body.