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How much vitamin B12 do we need and what's the best way to get it?

Dietitians discuss food sources of this essential nutrient and when a vitamin B12 supplement may help.
B12 collage of eggs, cheese and milk
If you have a very varied diet, it's not necessary for most people to take a supplement, Dana Hunnes told TODAY.TODAY illustration / Getty Images

Vitamin B12 is considered something of a hot health supplement — especially since COVID-19. In fact, a recent study conducted in Singapore that examined how B vitamins might help alleviate symptoms of COVID-19 found that patients who were given vitamin B12 supplements (500 μg), vitamin D (1,000 IU) and magnesium experienced a reduction in the severity of COVID-19 symptoms and the need for oxygen and intensive care support.

What is vitamin B12?

This essential nutrient works to preserve the health of your nerve and blood cells, according to the National Institutes of Health (NIH). Vitamin B12 also helps make DNA, the genetic material in all cells, and helps to prevent a type of anemia called megaloblastic anemia that makes people tired and weak.

What are the health benefits of vitamin B12?

“Vitamin B12 is essential for proper neurological and metabolic functioning, including the transport of oxygen in our bodies,” Whitney English, a registered dietitian based in Los Angeles, told TODAY. “B12 is used to make red blood cells, which carry oxygen in the body. What else are B12 vitamins good for? Vitamin B12 is also a ‘co-factor’ in DNA synthesis. Finally, B12 is required to make myelin, the protective layer that coats nerve cells.”

Our bodies need vitamin B12, but they don’t make it on their own, Dana Hunnes, Ph.D, a senior registered dietician at the Ronald Reagan University of California, Los Angeles Medical Center and professor at the UCLA Fielding School of Public Health, told TODAY. But if you have a very varied diet, it's not necessary for most people to take a supplement, she said. There are many different food sources of B12 vitamins.

You can get more of this nutrient in your diet by eating vitamin B12 foods like:

  • ​Nutritional yeast
  • Eggs
  • Cheese
  • Milk
  • Yogurt
  • Fortified non-dairy milks
  • Fortified breakfast cereals
  • Beef, liver and chicken
  • Fish, such as canned tuna, sockeye salmon and rainbow trout
  • Clams

Who is prone to vitamin B12 deficiency?

The recommended daily allowance of vitamin B12 for adults isn’t much — 2.4 mcg, according to the NIH. But since it’s mainly consumed through meat and fish, people on plant-based or vegan diets might want to consider a vitamin B12 supplement, as well as consuming foods fortified with vitamin B12.

Since vitamin B12 is absorbed through the small intestine, certain medical conditions, like celiac or Crohn’s disease, can interfere with its absorption. “You need intrinsic factor, a protein made in the stomach, to help absorb B12,” said Hunnes. “Surgery that removes or bypasses parts of the small intestine or stomach (gastrectomy) increase the risk for B12 deficiency. Autoimmune conditions, including Type 1 diabetes may also increase the risk for B12 deficiency if it affects the ability to absorb B12 from food.”

Those with gastroesophageal reflux disease (GERD) or acid reflux should also talk to their doctor about their vitamin B12 levels, as should older people, who are especially prone to a B12 deficiency because they don’t make as much stomach acid.

In some cases, low levels of vitamin B12 may be treated with injections of vitamin B12. Injections may also be used to help prevent vitamin B12 deficiencies in some people. Shots of vitamin B12 are typically injected subcutaneously (under the skin) or into a muscle. They're widely regarded as safe and don't tend to cause any B12 vitamin side effects. However, in some rare instances, a person could have an allergy or sensitivity to the injection that causes a reaction.

A vitamin B12 deficiency may cause symptoms like:

  • Fatigue
  • Anemia
  • Shortness of breath
  • Dizziness
  • Pale or yellowish skin
  • Depression
  • Soreness of the mouth and tongue
  • Irregular heartbeats
  • Weight loss
  • Difficulty maintaining balance
  • Neurological issues, such as tingling in your hands and feet
  • Muscle weakness
  • Personality changes
  • Unsteady movements
  • Mental confusion or forgetfulness

What to do if you think you’re vitamin B12 deficient

English said routine tests don’t always reveal the particulars of a vitamin B12 deficiency, so if you suspect you have one you should ask for a detailed panel at your primary care doctor’s office. Regardless, she recommended supplementing with B12 because it can take a lot more than the recommended daily allowance to actually absorb the right amount.

“Healthy adults following plant-based diets should supplement with at least 50 mcg (of) B12 per day or 2,000 mcg per week, and plant-based pregnant and breastfeeding women (should) supplement with at least 150 mcg per day,” said English.

And don’t worry, you’re not likely to overdo it, even at 2,000 mcg a week, said English. “There is no known level at which B12 is harmful. B12 is water-soluble and our body eliminates what it doesn't need.” Vitamin B12 does, however, have the potential to interact with certain medications, according to the NIH, so be sure to talk to your doctor before taking a B12 supplement.