What Happens to Your Body When You Take Vitamin B12 Every Day

Our body needs a variety of different vitamins and minerals to thrive, including eight different B vitamins. Out of all of them, vitamin B12 might be the most popular. Vitamin B12 is a water-soluble vitamin that contains the mineral cobalt, and is sometimes called cobalamin. It is naturally found in many animal-based foods and is added to fortified foods, like breakfast cereals.

“When a product is fortified with B12, a percent Daily Value will be listed on the food label in the vitamins and minerals section. Naturally occurring B12 is not listed on the food label,” says Grace Scarborough Wheeler, RDN, a dietitian based in Seattle.

B12 is a necessary nutrient for the development of the brain and nerve cells, red blood cells and DNA synthesis. Since it is not primarily found in plant foods—though some, like seaweed and mushrooms, can contain small amounts—it is essential for people who follow vegan and vegetarian diets to supplement or consume foods fortified with B12. 

Keep reading to learn more about vitamin B12, including its health benefits, which foods contain it, who should supplement and what to look for in the supplement.

Why We Love Vitamin B12

Red Blood Cell Production

Red blood cells carry oxygen from the lungs to other parts of the body and help remove carbon dioxide. Sufficient vitamin B12 is necessary for producing healthy red blood cells and preventing megaloblastic anemia, a type of anemia that causes large, underdeveloped red blood cells. Symptoms of megaloblastic anemia can include fatigue, pale skin, heart palpitations, loss of appetite, weight loss or infertility.

Brain and Nervous System Health

B12 is required for neurological function and maintaining healthy nerve cells. A vitamin B12 deficiency may interfere with maintaining the healthy functioning of the nervous system and could even lead to permanent nerve damage over time. 

Development for Infants

As an infant's brain develops rapidly, adequate B12 is needed to support healthy brain development and produce red blood cells. B12 is readily found in breast milk and is fortified into formulas, so infants' needs can be easily met from consuming these foods regularly. While rare, B12 deficiency can cause failure to thrive and delays in developmental milestones for infants. If left untreated, vitamin B12 deficiency could lead to permanent brain damage over time. If you have concerns about your child, be sure to talk to a health care professional. 

Healthy Energy Metabolism

Vitamin B12 plays an important role in energy metabolism. For this reason, if you have a vitamin B12 deficiency, you may feel tired or weak. The good news is that B12 deficiency is generally easy to treat, through increasing food sources, taking a supplement or, in cases of malabsorption, via high-dose injection or nasal spray. Oftentimes, treatments can work very quickly, within 48 to 72 hours. Talk to a health care professional to identify an individualized plan for you. 

While scientists are studying the effects of B12 supplementation on cancer, heart disease, stroke, dementia and as an adjunct therapy for viral infections, more evidence is needed to clarify its influence on long-term health. 

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Vitamin B12 Deficiency

Most people in the U.S. consume adequate amounts of B12. Data shows that only 4% of men and 8% of women in the U.S. had food and beverage intakes of B12 below the estimated average requirement (EAR). Following a vegan or vegetarian diet can make it more difficult to get enough vitamin B12 since the primary sources of it are animal-based. There are several other causes of vitamin B12 deficiency, as well. Some people may develop B12 deficiency if they do not consume enough B12 in their diet, have difficulty absorbing B12 from food, have a condition known as pernicious anemia, have had gastrointestinal surgery removing portions of the GI tract or have prolonged use of certain medications such as metformin, oral contraceptives, proton pump inhibitors and H2 blockers. However, because most people do consume enough through food and the body stores a significant amount of vitamin B12 in the liver, symptoms of B12 deficiency can sometimes take years to appear. 

How Much You Need

The Recommended Dietary Allowance (RDA) of vitamin B12 for adults 19 and older is 2.4 micrograms per day. However, if you are pregnant or lactating, the amount increases to 2.6 and 2.8 micrograms, respectively. 

The bioavailability—or extent a nutrient can be absorbed and accessed in the body—of B12 varies, depending on its source. For example, the bioavailability of B12 in dairy products is about three times higher than in meat, fish and poultry, while the bioavailability of B12 from supplements is 50% higher than from any food source. That said, including a variety of nutritious whole foods in your diet is the best way to meet your B12 and other nutrient needs. 

Food Sources

Since vitamin B12 is bound to protein, B12-rich food sources include:

• Fish, meat, poultry, eggs, dairy
• Clams, oysters, beef liver
• Fortified breakfast cereals, nutritional yeast and plant-based milk alternatives

“If you want to start adding more vitamin B12 food sources to your diet, find food sources that you actually enjoy. You are much more likely to continue eating them if they’re foods that can easily be added to your daily diet,” says Michelle Saari, M.S., RD, registered dietitian and nutrition writer. “Try to add at least one food source per day. This could mean having a bowl of fortified cereal with milk as a snack. You don’t need a source at every meal, but try adding more to your weekly diet, and try to add at least one source per day.”

“If you follow a vegan diet, use fortified nutritional yeast as well as fortified foods to supplement your diet. You can sprinkle it over pasta, pizza and salads for a cheesy flavor, or mix it into soups or stews,” says Laura M. Ali, M.S., RDN, a culinary nutritionist based in Pittsburgh.

Recipes to Try

Vegan Mac & Cheese

4.5

Spice-Roasted Sweet Potatoes over Garlicky Yogurt

5.0

Marry Me Chicken–Stuffed Spaghetti Squash

5.0

Is Vitamin B12 Safe for Everyone?

Since vitamin B12 is water-soluble, even large doses are generally considered safe because the body does not store more than it needs. Any excess gets flushed out in urine. However, large doses of vitamin B12 that are required to treat deficiency may cause side effects such as nausea, vomiting or diarrhea, and some people may develop itching or skin rash. Be sure to check with a health care professional before starting any high-dose supplements and follow up with them if you experience any side effects.

Vitamin B12 does have the potential to interact with certain medications, including medications used to treat gastroesophageal reflux (GERD) and peptic ulcer disease. This is because these medications slow the release of gastric acid in the stomach, and gastric acid is necessary for releasing B12 from food. Another common medication that can interfere with B12 absorption is metformin, commonly prescribed for those with prediabetes and diabetes. 

While it is rare, people who have sensitivities or allergies to B12, cobalt or other ingredients listed on the supplement label should avoid taking the supplement.

What to Look For in a Vitamin B12 Supplement

Vitamin B12 is available in multivitamin supplements, B-complex supplements and supplements containing only B12. The amount of B12 in supplements can vary widely, from 500 micrograms to 1,000 micrograms. “The most important thing when looking at a vitamin B12 supplement is the dosage to ensure that it is one that is appropriate for you,” says Saari. You should consult with a health care professional before starting any new supplement. 

There are several forms of B12, including adenosylcobalamin, methylcobalamin and hydroxycobalamin. “Methylcobalamin is a better-absorbed form of vitamin B12,” says Lisa Andrews, M.Ed., RD, LD, a consultant dietitian.

“If your budget allows, choose a product that is USP or NSF certified. It’s a (voluntary) independent verification that confirms the listed ingredients are really in there—without harmful levels of contaminants or heavy metals that shouldn’t be in there,” says Lori McCall, M.S., RD, LDN, registered dietitian and health writer.

Our Expert Take

Vitamin B12 is an essential, water-soluble vitamin that should be consumed through a variety of animal and/or fortified plant foods, or supplements. The health benefits of B12 include supporting a healthy brain, a healthy nervous system, red blood cell production and DNA synthesis. While B12 deficiency can be very serious if it goes untreated, especially for those who are pregnant or for developing infants, it is typically easily treatable through a variety of supplements, including food, pills, injections or sprays. It is difficult to overdose on B12, though there could be health consequences with very high doses.