Vitamin B12: What to Know

Medically Reviewed by Zilpah Sheikh, MD on June 29, 2024
Written by Kathryn Whitbourne
11 min read

Vitamin B12 does a lot of good things for your body. It helps create your DNA and red blood cells, for example. It's also needed to develop your central nervous system (your brain and spinal cord). And it helps keep your hair, nails, and skin healthy. Since vitamin B12 contains the mineral cobalt, it's sometimes known as cobalamin.

Your body doesn't make B12, so you have to get it from foods of animal origin, like meat, or from supplements. The vitamin is water-soluble, meaning your body lets out any excess through your pee. While B12 stores in the liver for up to 5 years, you can eventually become deficient (lacking) in it if you don't take in enough.

Vitamin B12 and red blood cells

You need B12 in order to make healthy red blood cells, white blood cells, and platelets. Every day, about 1% of your oldest red blood cells are destroyed and replaced. New red blood cells need vitamin B12 and folate (vitamin B9) to grow and develop. If these vitamins are lacking, making DNA is hard, causing the immature red blood cells to die. This leads to anemia.

Vitamin B12 and bone health

Several studies have positively linked B vitamins, including B12, with a lower risk of osteoporosis (a disease that weakens your bones) and hip fractures. But studies don't show that taking B supplements would prevent these bone problems.

Vitamin B12 and vision

A rare condition from a lack of vitamin B12 is optic neuropathy. This means that the optic nerve, the nerve that transmits visual information from the eye to the brain, is damaged. This can lead to a gradual loss of vision, as well as to your seeing blind spots. Less than 1% of people with B12 deficiency report getting optic neuropathy.

Vitamin B12 and depression

Several studies show a link between depression and low levels of B12 but not a link between increasing the levels of B12 and a reduction in depression symptoms. But it could be helpful to screen people for B12 deficiency in advance and give B12 supplements to delay or prevent the onset of depression to those with lower levels of the vitamin in their bodies. More research is needed.

Vitamin B12 and memory

Vitamin B12 deficiency is associated with cognitive problems (problems with thinking, judgement, and learning) and memory issues and may play a role in getting Alzheimer's disease and stroke. One study gave B12 vitamins to people with mild cognitive issues and low levels of B12 and showed that most people improved their cognitive symptoms. However, other studies haven't seen a connection between low levels of B12 and cognitive problems or an improvement in these symptoms after getting extra doses of B12. This is an area where more research is clearly needed.

Vitamin B12 and energy

You may see energy drinks with labels boasting that they've lots of vitamin B12 in their products. Certain vitamins, including B12, have an effect on fatigue and a lack of energy. If you feel constantly tired and your levels of B12 are low, bringing them up to normal may give you more energy, studies show. But B12 supplements doesn't seem to have any effect on people already at normal levels. In other words, if you're tired and already have normal levels of B12 in your body, drinking that energy drink probably won't make you feel any better.

Vitamin B12 and skin

If you have a very low level of B12, you may be subject to hyperpigmentation (dark spots) on your skin, as well as to vitiligo (light patches on your skin), mouth ulcers, eczema, and acne. On the other hand, too much B12 in your body can also give you vitiligo, mouth ulcers, eczema, and acne.

Vitamin B12 and hair

B12 deficiency is associated with hair loss, but there's not enough evidence to show that taking B12 supplements will help hair grow back.

Vitamin B12 and nails

If you have too little B12 in your body, your nails might turn brown-gray or bluish. This should change when you up your B12 levels to normal. There are no studies showing that taking B12 if your levels are normal will help your nails grow stronger or longer.

How much of this vitamin should you get?

The answer depends on things like your age, eating habits, health conditions, and what medications you take.

The average recommended daily amounts, measured in micrograms, vary by age:

  • Infants up to age 6 months: 0.4 micrograms
  • Babies aged 7-12 months: 0.5 micrograms
  • Children aged 1-3 years: 0.9 micrograms
  • Kids aged 4-8 years: 1.2 micrograms
  • Children aged 9-13 years: 1.8 micrograms
  • Teens aged 14-18 years: 2.4 micrograms
  • Adults (19+ years): 2.4 micrograms
  • Pregnant: 2.6 micrograms
  • Breastfeeding: 2.8 micrograms

You can get vitamin B12 from animal foods, which have it naturally, or from foods that have been fortified with it. These include:

  • Meat
  • Fish
  • Poultry
  • Milk
  • Eggs
  • Fortified breakfast cereals
  • Fortified breads
  • Nutritional yeasts
  • Fortified plant milks

If you think you might be low on B12, ask your doctor about getting a blood test to check your vitamin B12 level. You're more likely to have vitamin B12 deficiency if you have a medical condition where your body can't absorb B12 or you follow a strict vegan diet.

Vitamin B12 and pernicious anemia

Pernicious anemia is an autoimmune disease in which your body can't make intrinsic factor, a protein needed to absorb B12. So even if you're eating a lot of meat or taking vitamin supplements, you're not absorbing B12. Pernicious anemia is the most common cause of B12 deficiency.

Intestinal malabsorption

Conditions that affect your small intestines like Crohn's disease, celiac disease, bacterial growth, or a parasite can lead to vitamin B12 deficiency. So can having an autoimmune disease called atrophic gastritis, in which your stomach lining has thinned. This means your body doesn't make enough hydrochloric acid and intrinsic factor in your stomach, both needed to absorb B12. (Hydrochloric acid separates B12 from the protein it's attached to in food; the freed B12 combines with intrinsic factor so that the body can absorb the vitamin.)

Vitamin B12 and alcohol

Misusing alcohol or drinking heavily can make it harder for your body to absorb nutrients, including B12. Drinking too much alcohol can also prevent you from eating enough calories.

Vitamin B12 and immune system

Your body's immune system fights off illnesses and infections. When you have an autoimmune disease, your immune system starts attacking healthy cells. Immune system disorders, such as Graves' disease or lupus, are linked with vitamin B12 deficiency. This may be because people who have them tend to also have pernicious anemia or atrophic gastritis, which prevent absorption of the nutrient.

Medication interactions

Taking certain medicines can interfere with the absorption of vitamin B12. These include:

  • Some heartburn medicines like proton pump inhibitors such as esomeprazole (Nexium), lansoprazole (Prevacid), omeprazole (Prilosec OTC), pantoprazole (Protonix), and rabeprazole (Aciphex)
  • H2 blockers such as famotidine (Pepcid AC)
  • Metformin (Glucophage), taken for diabetes
  • Colchicine, taken for gout
  • Some chemotherapy drugs, especially methotrexate

Vitamin B12 and vegan diet

If you follow a vegan diet (meaning you don't eat any animal products, including meat, milk, cheese, and eggs) or you're a vegetarian who doesn't eat enough eggs or dairy products, you could be lacking in vitamin B12. You can add fortified foods to your diet or take supplements to meet this need.

Other reasons for vitamin B12 deficiency

With age, it can become harder to absorb this vitamin. Many people over 50 don't make enough hydrochloric acid in their stomachs to absorb B12 from foods, though they can absorb it from supplements. 

If you've had weight loss surgery or another operation that removed part of your stomach, you might no longer make enough hydrochloric acid and intrinsic factor to absorb vitamin B12.

Your doctor may offer vitamin B12 injections if you're very anemic. You'll usually take them every day for 2 weeks until your symptoms start improving. Then you may be able to switch to B12 supplements. 

If your B12 deficiency is due to an autoimmune disease or something else not related to diet, you may need to get injections every two or three months for the rest of your life. 

The injections are usually given in your upper arm or thigh, or into a muscle. Your doctor or nurse may do the shots or show you how to do them yourself. Side effects are usually minor but if your ankles start to swell, or you have an allergic reaction or trouble breathing, call your doctor.

If your B12 levels are already normal, getting a B12 injection for extra energy or weight loss isn't going to help. No studies have shown any benefit to extra B12 in these areas. 

 

Your doctor will advise vitamin B12 supplements if your B12 levels are low but not severe. These are available at the drugstore on their own or as part of a B-complex vitamin or a multivitamin. You can buy the supplements to swallow as pills, to dissolve under your tongue, or as nasal sprays.

Although some of the supplement doses are very high (for instance, 500 or 1,000 micrograms when a healthy adult only needs 2.4 micrograms per day), your body only absorbs what it needs and pees the rest out. 

One advantage of supplements is that your body doesn't need to have hydrochloric acid in the stomach to separate the B12 from the protein it's attached to the way it does for food. But it does need to combine with intrinsic factor to be absorbed in your body.

So if your vitamin B12 deficiency is due to an autoimmune disease in which your stomach doesn't make intrinsic factor, you likely can't take supplements and will need injections.

Are you pregnant, on a vegan or vegetarian diet, and plan to only breastfeed your baby? Talk to your doctor so that you'll have a plan for how you'll get enough vitamin B12 to keep your baby healthy.

Without enough vitamin B12, your baby could have developmental delays and not thrive the way they should. B12 is very important for brain and spinal development.

Your body stores 1,000-2,000 times as much vitamin B12 as you'd eat in a day, so it can take many years to see symptoms of vitamin B12 deficiency.

If you have vitamin B12 deficiency, you could become anemic. A mild deficiency may cause no symptoms. But if untreated, it may lead to the following symptoms:

Physical symptoms of vitamin B12 deficiency

  • Weakness, tiredness, or lightheadedness
  • Heart palpitations and shortness of breath
  • Pale skin
  • A painful, smooth, inflamed tongue (glossitis)
  • Constipation, diarrhea, loss of appetite, or gas
  • Bluish or gray-brown nails.
  • Loss of appetite

Neurological symptoms of vitamin B12 deficiency

  • Numbness or tingling
  • Muscle weakness
  • Problems walking or speaking
  • Vision loss
  • Difficulty remembering things

Other symptoms of vitamin B12 deficiency

  • Depression
  • Mood swings
  • Irritability

Treatment depends on the reason for the low levels of B12.

If you have pernicious anemia or have trouble absorbing vitamin B12 due to a disease, you'll need shots of this vitamin at first. You may need to keep getting these shots, take high doses of a supplement by mouth, or get it nasally after that.

If it's due to diet, you can start eating more meat, fish, and dairy products. If you don't eat animal products, you can change your diet to include vitamin B12–fortified breads and cereals or B12 supplements.

Older adults who have vitamin B12 deficiency will likely have to take a daily B12 supplement or a multivitamin that contains B12.

If it's due to taking a medication, talk to your doctor about changing to other drugs. Or if drinking too much alcohol is the problem, discuss that with your doctor too.

For most people, treatment resolves the problem. But nerve damage that happened due to the lack of B12 could be permanent.

Vitamin B12 deficiency due to diet is rare in the U.S. Most people can prevent it by eating enough meat, poultry, seafood, dairy products, and eggs.

If you don't eat animal products, or you have a medical condition that limits how well your body absorbs nutrients, you can take vitamin B12 in a supplement or eat plant-based foods fortified with B12.

If you take vitamin B12 supplements, let your doctor know so they can tell you how much you need, and make sure they won't affect any medicines you're taking.

Avoid drinking too much alcohol. Men shouldn't drink more than two drinks a day, and women shouldn't drink more than one drink a day.

 

There's no established upper level for B12 because even if you take large amounts of it, your body won't store more than it needs to. One study had people on doses as high as 2,000 micrograms with no side effects.

However, there have been cases of people breaking out into acne and rosacea and having heart palpitations after taking very high doses of vitamin B12, usually by injection. Research from 2020 found that the death rate among people in the study with the highest levels of B12 in their bodies was almost twice that of those with the lowest levels of B12. The researchers weren't sure why.

Vitamin B12 is important for making DNA and red blood cells, as well as for developing the central nervous system. Too little B12 in your body can affect your bones, hair, skin, nails, energy level, mood, and memory. You can only get it naturally from animal products like meat and dairy. People who are on a strict vegetarian or vegan diet or who have certain medical conditions may lack B12. But they can get it from B12 supplements or fortified cereals and breads. Because your body stores B12, it can take some years before you see symptoms that you're low on it.

Which food is highest in B12?

Beef liver. Three ounces of cooked beef liver has 70.7 micrograms of vitamin B12. That's 2,944% of your recommended daily allowance of B12! In general, organ meats, like kidneys or livers from animals, are very high in B12. If you don't like organ meats, your next best bet is clams. Three ounces cooked without shells has 17 micrograms or 708% of your recommended daily allowance of B12.

What is the fastest way to fix B12 deficiency?

The fastest way is to change your diet. Liver, clams, oysters, nutritional yeast, salmon, tuna, and ground beef are all very high in vitamin B12. Another option is start taking B12 supplements which usually have megadoses of the vitamin.

What are the four stages of B12 deficiency?

The stages are:

  • Stage I: Low serum level. You have low levels of vitamin B12 in your blood. You have no B12 deficiency symptoms.
  • Stage II: Low cell-store. You have low levels of B12 in your cells.
  • Stage III: Biochemical deficiency. You have higher levels of the chemicals homocysteine and methylmalonic acid and decreased DNA synthesis, leading to neurological and psychological symptoms, like confusion, mood swings, problems walking or talking, and irritability.
  • Stage IV: Clinically evident deficiency. You get macrocytic anemia or very large red blood cells. These aren't functioning properly. You usually feel tired and weak, as well as have the earlier neurological and psychological symptoms.