Vitamin B12: What to Know

Written by Kathryn Whitbourne
Medically Reviewed by Jabeen Begum, MD on April 30, 2025
10 min read

Vitamin B12 is a nutrient that your body doesn't make, so you have to get it from animal products, such as meats, dairy, and eggs, or from supplements. B12 is important because it keeps your nerve and blood cells healthy. The vitamin is water-soluble, meaning your body expels any excess through your pee. While B12 can be stored in your liver for up to five years, you can become deficient (lacking) in it if you don't get enough. Since vitamin B12 contains the mineral cobalt, it's sometimes known as cobalamin.

Vitamin B12 does a lot of important things for your body. It helps create your DNA and red blood cells, for example. Your body also needs B12 for the development of your central nervous system (your brain and spinal cord). It also helps keep your hair, nails, and skin healthy. 

Bone and red blood cell health

You need B12 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 you're lacking these vitamins, making DNA is hard, causing the immature red blood cells to die. This leads to anemia.

Several studies have linked B vitamins, including B12, to a lower risk of osteoporosis (a disease that weakens your bones) and hip fractures. But there’s no evidence that taking B supplements would prevent these bone problems.

Vitamin B12 for 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 cause a gradual loss of vision and result in blind spots. Less than 1% of people with B12 deficiency report getting optic neuropathy.

Improved mood and memory

Although several studies show a link between depression and low B12 levels, there's no evidence that increasing the levels of B12 can help ease depression symptoms. But it could be helpful to screen people for B12 deficiency in advance and give them B12 supplements to delay or prevent the onset of depression. More research is needed to confirm this.

Vitamin B12 deficiency is associated with cognitive problems (problems with thinking, judgment, and learning) and memory issues. So, it may play a role in conditions such as Alzheimer's disease and stroke. One study found that when people with mild cognitive issues and low levels of B12 were given B12 vitamins, most of them showed improved cognitive symptoms. However, other studies haven't seen a link between low levels of B12 and cognitive problems or an improvement in these symptoms after getting extra doses of B12. This is an area that requires further research.

Better energy levels

You may see energy drinks with labels boasting that they've lots of vitamin B12 in their products. Certain vitamins, including B12, can affect people who have 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 don'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 for hair, skin, and nails

If you have a very low level of B12, you may be prone to hyperpigmentation (dark spots) on your skin, 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.

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

If you have too little B12 in your body, your nails might turn brown-gray or bluish. This should change when you bring 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.

Making sure you get the right amount of vitamin B12 depends on things such as your age, eating habits, health conditions, and the medications you take.

Vitamin B12 dosage

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

Vitamin B12 foods

You can get vitamin B12 from animal products, 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
  • Fortified nutritional yeasts
  • Fortified plant milks

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.

Vitamin B12 injections

Your doctor may offer vitamin B12 injections if you're very anemic. You'll usually take them every day for two 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 that's 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 give you the shots or show you how to take 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 that extra B12 offers any benefits in these areas.

Vitamin B12 supplements

If your B12 levels are low but not severe, your doctor will suggest you take vitamin B12 supplements. 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, as it does for food. But it does need to combine with intrinsic factor, a protein made by your stomach, to be absorbed into your body.

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

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 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 deficiency symptoms

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

What happens if your vitamin B12 deficiency is left untreated?

If you don't treat your B12 deficiency, it can lead to more severe neurological problems, including:

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

Treating vitamin B12 deficiency

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

Several autoimmune diseases can make it harder for your body to absorb B12, including pernicious anemia. It's when your body can't make intrinsic factor, the protein needed to absorb B12. Another autoimmune disease, atrophic gastritis, thins the lining of your stomach and prevents your body from making enough hydrochloric acid and intrinsic factor you need to absorb B12. To treat them, you'll probably need shots of vitamin B12 at first, and then you may need to keep getting shots, or taking high doses of a supplement by mouth or nasally. Immune system disorders, such as Graves' disease or lupus, are also linked to vitamin B12 deficiency.

If your B12 deficiency is because of your 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.

Taking certain medicines can interfere with how your body absorbs vitamin B12. These include some heartburn medicines, including esomeprazole (Nexium), famotidine (Pepcid AC), lansoprazole (Prevacid), omeprazole (Prilosec OTC), pantoprazole (Protonix), rabeprazole (Aciphex), as well as some diabetes, gout, and chemotherapy drugs. So, talk to your doctor if you take any of these. You might have to take a B12 supplement or try a new medication.

For most people, treatment resolves the problem. But if you have nerve damage from your lack of B12, it could be permanent.

How to prevent vitamin B12 deficiency

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. Drinking heavily can make it harder for your body to absorb nutrients, including B12. Too much alcohol can also prevent you from getting enough calories. Men shouldn't drink more than two drinks a day, and women shouldn't drink more than one drink a day.

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

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

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. A 2020 study found that the death rate among people with the highest levels of B12 in their bodies was almost twice as high as that of people 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 the growth of 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 on a strict vegetarian or vegan diet or those with 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. A 3-ounce serving 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 of cooked clams without shells provide 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 to 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 reduced DNA synthesis, leading to neurological and psychological symptoms, such as confusion, mood swings, problems walking or talking, and irritability.

Stage IV. Clinically evident deficiency. You get macrocytic anemia or very large red blood cells, which don't work properly. You usually feel tired and weak. You also have the neurological and psychological symptoms of stage III.