Vitamin B12 is a nutrient that helps keep the body's nerve and blood cells healthy and helps make DNA, the genetic material in all cells. Vitamin B12 also helps prevent a type of anemia called megaloblastic anemia that makes people tired and weak.

The amount of vitamin B12 you need each day depends on your age. Average daily recommended amounts for different ages are listed below in micrograms (mcg):

Vitamin B12 is found naturally in a wide variety of animal foods and is added to some fortified foods. Plant foods have no vitamin B12 unless they are fortified. You can get recommended amounts of vitamin B12 by eating a variety of foods including the following:

• Beef liver and clams, which are the best sources of vitamin B12.
• Fish, meat, poultry, eggs, milk, and other dairy products, which also contain vitamin B12.
• Some breakfast cereals, nutritional yeasts and other food products that are fortified with vitamin B12. To find out if vitamin B12 has been added to a food product, check the product labels.

Vitamin B12 is found in almost all multivitamins. Dietary supplements that contain only vitamin B12, or vitamin B12 with nutrients such as folic acid and other B vitamins, are also available. Check the Supplement Facts label to determine the amount of vitamin B12 provided.

Vitamin B12 is also available in sublingual forms (which are dissolved under the tongue). There is no evidence that sublingual forms are better absorbed than pills that are swallowed.

A prescription form of vitamin B12 can be administered as a shot. This is usually used to treat vitamin B12 deficiency. Vitamin B12 is also available as a prescription medication in a nasal gel form that is sprayed into the nose.

Most people in the United States get enough vitamin B12 from the foods they eat. But some people have trouble absorbing vitamin B12 from food. The body absorbs vitamin B12 from food in a two-step process. First, hydrochloric acid in the stomach separates vitamin B12 from the protein that it’s attached to. Second, the freed vitamin B12 then combines with a protein made by the stomach, called intrinsic factor, and the body absorbs them together.

Vitamin B12 in dietary supplements isn’t attached to protein and doesn’t require the first step. However, B12 in supplements does need to combine with intrinsic factor to be absorbed.

People with pernicious anemia, an autoimmune disease, can’t make intrinsic factor. As a result, they have trouble absorbing vitamin B12 from foods and dietary supplements.

Vitamin B12 deficiency affects between 3% and 43% of older adults. Your doctor can test your vitamin B12 level to see if you have a deficiency.

Certain groups of people may not get enough vitamin B12 or have trouble absorbing it:

• Many older adults don’t have enough hydrochloric acid in their stomach to absorb the vitamin B12 that’s naturally present in food. People over 50 should get most of their vitamin B12 from fortified foods or dietary supplements because, in most cases, their bodies can absorb vitamin B12 from these sources.
• People with an autoimmune disease called atrophic gastritis might not absorb enough vitamin B12 because they make too little hydrochloric acid and intrinsic factor in their stomach.
• People with pernicious anemia do not make the intrinsic factor needed to absorb vitamin B12. As a result, they have trouble absorbing vitamin B12 from foods and dietary supplements. Doctors usually treat pernicious anemia with vitamin B12 shots, although very high doses of vitamin B12 given by mouth might also be effective.
• People who have had some types of stomach or intestinal surgery (for example, to lose weight or to remove part or all of the stomach) might not make enough hydrochloric acid and intrinsic factor to absorb vitamin B12.
• People with disorders of the stomach and small intestine, such as celiac disease or Crohn’s disease, might not absorb enough vitamin B12.
• People who eat little or no animal foods, such as vegetarians and vegans, might not get enough vitamin B12 from their diets. Only animal foods have vitamin B12 naturally. When pregnant women and women who breastfeed their babies are strict vegetarians or vegans, their babies might also not get enough vitamin B12.

Vitamin B12 deficiency causes tiredness, weakness, constipation, loss of appetite, weight loss, and megaloblastic anemia. Nerve problems, such as numbness and tingling in the hands and feet, can also occur. Other symptoms of vitamin B12 deficiency include problems with balance, depression, confusion, dementia, poor memory, and soreness of the mouth or tongue. Vitamin B12 deficiency can damage the nervous system even in people who don't have anemia, so it is important to treat a deficiency as soon as possible.

In infants, signs of a vitamin B12 deficiency include failure to thrive, problems with movement, delays in reaching the typical developmental milestones, and megaloblastic anemia.

Large amounts of folic acid can hide a vitamin B12 deficiency by correcting megaloblastic anemia, a hallmark of vitamin B12 deficiency. But folic acid does not correct the progressive damage to the nervous system that vitamin B12 deficiency also causes. For this reason, healthy adults should not get more than 1,000 mcg of folic acid a day.

Scientists are studying vitamin B12 to understand how it affects health. Here are several examples of what this research has shown.

Cancer
Some research shows that people with high levels of vitamin B12 have a higher risk of cancer. But other research shows that the risk of cancer is higher in people with low levels of vitamin B12 or that vitamin B12 levels don’t affect cancer risk. More evidence is needed to understand whether vitamin B12 levels affect cancer risk.

Heart disease and stroke
Vitamin B12 supplements (along with other B vitamins) reduce blood levels of homocysteine, a compound linked to an increased risk of having a heart attack or stroke But despite reducing homocysteine, research shows that these vitamins don’t reduce the risk of developing cardiovascular disease or stroke.

Dementia and cognitive function
Most studies show that low blood levels of vitamin B12 don’t affect the risk of cognitive decline in older people, regardless of whether they have dementia or Alzheimer’s disease. More clinical trials are needed to better understand the effects of vitamin B12 supplementation on cognitive function in older adults.

Energy and Endurance
Manufacturers often promote vitamin B12 supplements for energy, athletic performance, and endurance. But vitamin B12 doesn’t provide these benefits in people who get enough B12 from their diet.

Vitamin B12 has not been shown to cause any harm.

Yes. Vitamin B12 can interact or interfere with medicines that you take, and in some cases, medicines can lower vitamin B12 levels in the body. Here are several examples of medicines that can interfere with the body's absorption or use of vitamin B12:

• Chloramphenicol (Chloromycetin®), an antibiotic that is used to treat certain infections.
• Proton pump inhibitors, such as omeprazole (Prilosec®) and lansoprazole (Prevacid®), that are used to treat acid reflux and peptic ulcer disease.
• Histamine H2 receptor antagonists, such as cimetidine (Tagamet®), famotidine (Pepcid®), and ranitidine (Zantac®), that are used to treat peptic ulcer disease.
• Metformin, a drug used to treat diabetes.

Tell your doctor, pharmacist, and other healthcare providers about any dietary supplements and medicines you take. They can tell you if those dietary supplements might interact or interfere with your prescription or over-the-counter medicines or if the medicines might interfere with how your body absorbs, uses, or breaks down nutrients.

Most people have heard of vitamin B12, but did you know that it is naturally present only in animal foods like fish, meat, poultry, eggs, and milk? That’s right––plant foods, such as fruits, vegetables, beans, and rice have no natural vitamin B12.

Our bodies need vitamin B12 to keep nerve and blood cells healthy and to make DNA, the genetic material in all cells. Most adults need 2.4 micrograms (mcg) per day, and if you are pregnant or breastfeeding, you need a little more.

It’s not hard to get enough vitamin B12. A 3-ounce serving of ground beef, for example, has 2.4 mcg and 1 cup of milk has 1.3 mcg. But if you follow a vegan diet, you might fall short. Thankfully, some fortified foods––including some breakfast cereals and nutritional yeasts––have added vitamin B12. Many dietary supplements, including multivitamins and B-complex vitamins, also contain vitamin B12.

Keep reading to learn more about this important nutrient. 

Q. What happens if I don’t get enough vitamin B12?

A. A deficiency of vitamin B12 can cause a form of anemia called megaloblastic anemia. This can leave you feeling tired and weak. Vitamin B12 deficiency can also cause pale skin, heart palpitations, loss of appetite, weight loss, and infertility. In addition, you might have numbness or tingling in your hands and feet, soreness in your mouth and tongue, problems with balance, confusion, and depression.

Your healthcare provider can test the amount of vitamin B12 in your blood. If you have a deficiency, it is often treated with vitamin B12 supplements and sometimes vitamin B12 injections.  

Q. I am 58 and my doctor recommended a vitamin B12 supplement because of my age. Why is that?

A. Your body needs stomach acid to digest and absorb the vitamin B12 that’s naturally present in food. Many older adults have low levels of stomach acid and this can reduce vitamin B12 absorption from food. In addition, antacids such as Prilosec^® and Tagamet^® neutralize stomach acid which can interfere with vitamin B12 absorption.

It’s easier for your body to absorb the vitamin B12 in fortified foods and dietary supplements, so people over 50 should get most of their vitamin B12 from these sources. This might be why your doctor recommended a vitamin B12 supplement.  

Q. Is there anything else besides age that affects how well people absorb vitamin B12?

A. Yes. In addition to stomach acid, your body needs a protein called intrinsic factor to absorb vitamin B12. People with conditions called pernicious anemia or atrophic gastritis have trouble absorbing vitamin B12 because they don’t make enough stomach acid or intrinsic factor. In addition, people who have had some types of stomach or intestinal surgery, or those who have conditions such as celiac disease or Crohn’s disease, might not absorb enough vitamin B12.

If you have one of these conditions, your healthcare provider might recommend vitamin B12 injections or very high doses of vitamin B12 supplements.

Q. I know that dairy products like milk, yogurt, and cheese contain vitamin B12, but why isn’t it listed on the Nutrition Facts labels?

A. Food labels are not required to list vitamin B12 unless it has been added to the food. Therefore, you can’t rely on product labels to learn if a food naturally contains vitamin B12 and if so, how much.

As noted above, one cup of milk contains 1.3 mcg of vitamin B12. That’s a little over 50% of the Daily Value (DV). Six ounces of plain yogurt has 1.0 mcg and 1 ½ ounces of cheddar cheese has 0.5 mcg.

Q. My vitamin B12 supplement contains 41,667% of the DV. Is that much safe?

A. Yes, it’s safe. The product you have contains 1,000 mcg of vitamin B12. The DV is only 2.4 mcg, so 1,000 mcg is 41,667% of the DV or over 400 times the amount you need. Because vitamin B12 is considered safe at any dose, taking 1,000 mcg shouldn’t cause any health problems, but we always recommend talking with your healthcare provider.