What Happens to Your Body When You Take Vitamin B12

You may be aware of the various B vitamins and know that you need them, but what exactly is B12 and do you need to take it every day? B12 supplements are most often seen marketed to boost your energy and mood, but this vitamin plays a far more critical role in the body. It is an essential vitamin necessary for producing healthy red blood cells, nerve and brain function, and making DNA, the genetic material contained in all your cells. While most people get enough B12 through a variety of foods, a supplement to prevent deficiency generally won’t cause harm. Additionally, it may be beneficial for some populations to supplement with B12, including those who follow a vegan or vegetarian diet or have conditions that cause malabsorption of B12. 

What Is Vitamin B12?

Vitamin B12 is a water soluble vitamin that contains the mineral cobalt, so are sometimes called cobalamins. It is naturally found in some foods like tuna, beef and dairy, added to fortified foods like breakfast cereals, and available as a dietary supplement or prescription. B12 is a necessary nutrient for the development of the brain and nerve cells, red blood cells and DNA synthesis. Since it is not naturally occurring in plant foods, it is essential for people who follow a vegan and vegetarian diet to supplement or consume foods fortified with B12. 

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). There are several causes of vitamin B12 deficiency. 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 or prolonged use of certain medications. 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 can sometimes take years to appear. 

Recommended Daily Intake of B12

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 depends on its source. For example, the bioavailability of B12 in dairy products is about 3 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. 

Health Benefits of Vitamin B12

Research has shown that vitamin B12 plays a role in your health. Some benefits include:

Red Blood Cell Production

Sufficient vitamin B12 is necessary for producing healthy red blood cells and preventing megaloblastic anemia, a type of anemia that causes large, underdeveloped 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 myelin synthesis. Therefore, B12 deficiency can interfere with the maintaining healthy function 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 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 your doctor and healthcare team. 

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, either via supplement, injection or nasal spray. Oftentimes, treatments can work very quickly, within 48 to 72 hours. Talk to your doctor to identify an individualized plan for you. 

While scientists are studying the effects of B12 supplementation on cancer, heart disease, stroke, dementia or adjunct therapy for viral infections, more evidence is needed to clarify its influence on longterm health. 

Food Sources of Vitamin B12

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, health specialist at eHealth Project, “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, PA. We couldn’t agree more, and love including it in recipes like our Vegan Mac & Cheese and our Vegan Chickpea Fritatta. 

“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, RDN, CD, a dietitian based in Seattle, WA. “Although label reading can be confusing, checking labels and choosing plant-based products that are high in B12 can help increase the amount you get in your diet.”

Potential Risks and Side Effects

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 your healthcare provider before starting any high-dose supplements and to follow up if you experience any side effects.

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

Who Should Take a Vitamin B12 Supplement?

While most people get enough from food sources in their diets, people with vitamin B12 deficiency or the following  circumstances should consider taking a supplement: 

• Avoid animal foods: Since B12 is only naturally found in animal foods, studies have shown that those following vegetarian and vegan diets tend to have low B12 stores. This is especially important for those who are pregnant since it is necessary for proper fetal brain and nerve system development. 
• Lack of intrinsic factor: Pernicious anemia is an autoimmune disease that impairs the gut’s ability to produce intrinsic factor, which is a protein that is necessary for the absorption of B12.
• Low stomach acid or medications that decrease stomach acid: Lack of sufficient stomach acid is the most common cause of B12 deficiency, especially for older adults. And vitamin B12 deficiency affects between 3% and 43% of older adults. Certain medications that reduce or suppress stomach acid taken regularly, such as medications and antacids for gastroesophageal reflux disease (GERD) or peptic ulcer disease, can cause difficulty absorbing vitamin B12 from food. However, fortified foods or supplements do not require stomach acid and can be an excellent choice for people who take these medications. 
• Intestinal surgery or digestive disorders: Surgery that impacts parts of the stomach or small intestine or diseases including Crohn’s and celiac disease can cause impaired or malabsorption of B12. Talk to your doctor about the best care plan for you. 
• Other medications that interfere with absorption: Metformin, a commonly-prescribed drug for prediabetes and diabetes, can block absorption of B12 and is strongly associated with B12 deficiency. 

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 your healthcare provider before starting any new supplement. 

There are several forms of B12 including adenosylcobalamin, methylcobalamin and hydroxycobalamin. However, “Methylcobalamin is a better-absorbed form of vitamin B12,” says Lisa Andrews, M.Ed., RD, LD, a registered dietitian nutritionist at the Health Insiders.

“If your budget allows, choose a product that is USP or NSF certified. It’s a (voluntary) third-party 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.

The Bottom Line

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 developing infants, it is typically easily treatable through a variety of supplements, including food, pills, injections or sprays, and even high doses are generally considered safe.