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Everything you need to know about  Vitamin B12                 

Picture Credit: “Alan Turing exhibition: Model of vitamin B12 by Dorothy Hodgkin” by p_a_h is marked with CC BY 2.0.
What is Vitamin B12?

To stay healthy, your body needs vitamin B12. Vitamin B12 does a lot of things for your body. For example, it helps make your DNA and your red blood cells and is crucial for nerve tissue health and brain function. The trouble is that your body doesn’t make vitamin B12, so you have to get it regularly from animal-based foods or supplements. Another name for vitamin B12 is Cobalamin. Chemically, vitamin B12 can exist in several different forms, but all contain the mineral cobalt[1].

While B12 is stored in the liver for up to five years, you can eventually become deficient if your diet doesn’t help maintain the necessary levels. Like all other B vitamins, vitamin B12 is water-soluble – meaning it can dissolve in water and travel through the bloodstream. The human body can get rid of any excess or unwanted vitamin B12 through urination.

Vitamin B12 is the largest and most structurally complicated vitamin[2]. Vitamin B12 is a manufactured form of vitamin B12. According to one author, it is important to treat vitamin B12 deficiency with hydroxocobalamin or cyanocobalamin or a combination of adenosylcobalamin and methylcobalamin, and not methylcobalamin alone[3].

Deficiency of Vitamin B12
A deficiency in vitamin B12 can lead to various health problems, ranging from tiredness to permanent neurological changes if left untreated. A deficiency (or insufficiency) occurs when levels of the vitamin become too low to meet the body’s demands. In the United States and the United Kingdom, approximately 6% of adults aged 60 or younger have vitamin B12 deficiency. In people older than 60, the rate jumps to 20%.[4]

Vitamin B12 or Folate Deficiency Anaemia[5]
Vitamin B12 or B9 (commonly called folate) deficiency anaemia occurs when a lack of vitamin B12 or folate causes the body to produce abnormally large red blood cells that cannot function properly:

  • Red blood cells carry oxygen around the body using a substance called haemoglobin.
  • Anaemia is the general term for having either fewer red blood cells than normal or having an abnormally low amount of haemoglobin in each red blood cell.

There are several different types of anaemia, and each one has a different cause. For example, iron deficiency anaemia happens when the body does not contain enough iron.

When to see a GP
You should see a GP if you think you may have a vitamin B12 or folate deficiency.

The conditions can often be diagnosed based on your symptoms and the results of a blood test.

It’s important for vitamin B12 or folate deficiency anaemia to be diagnosed and treated as soon as possible.

Although many of the symptoms improve with treatment, some problems caused by the condition can be irreversible.

Causes of a vitamin B12 or folate deficiency
Several problems can lead to a vitamin B12 or folate deficiency, including:

  • pernicious anaemia – where your immune system attacks healthy cells in your stomach, preventing your body from absorbing vitamin B12 from the food you eat; this is the most common cause of vitamin B12 deficiency in the UK.
  • A lack of these vitamins in your diet – although it is uncommon, it can happen if you have a vegan diet and do not take vitamin B12 supplements or eat foods fortified with vitamin B12, or follow a fad diet or have a generally poor diet for a long time.
  • Medicine – certain medicines, including anticonvulsants and proton pump inhibitors (PPIs), can affect how much of these vitamins your body absorbs.

Both vitamin B12 deficiency and folate deficiency are more common in older people, affecting around 1 in 10 people aged 75 or over and 1 in 20 people aged 65 to 74.

Treating vitamin B12 or folate deficiency anaemia
Most vitamin B12 and folate deficiency cases can be easily treated with injections or tablets to replace the missing vitamins. Vitamin B12 supplements are usually given by injection at first. Then, depending on whether your B12 deficiency is related to your diet, you’ll either require B12 tablets between meals or regular injections. These treatments may be needed for the rest of your life.

Folic acid tablets are used to restore folate levels. These usually need to be taken for four months.

In some cases, improving your diet can help treat the condition and prevent it from returning.

Vitamin B12 is found in meat, fish, eggs, dairy products, yeast extract (such as Marmite) and specially fortified foods. The best sources of folate include green vegetables, such as broccoli, brussels sprouts and peas.

Complications of vitamin B12 or folate deficiency anaemia
Although it’s uncommon, vitamin B12 or folate deficiency (with or without anaemia) can lead to complications, particularly if you have been deficient in vitamin B12 or folate for some time. Potential complications can include:

  • problems with the nervous system
  • temporary infertility
  • heart conditions
  • pregnancy complications and congenital disabilities

Adults with severe anaemia are also at risk of developing heart failure.

Some complications improve with appropriate treatment, but others, such as problems with the nervous system, can be permanent.

General Vitamin B12 Deficiency[6]
Most people in the US and the United Kingdom get enough vitamin B12, but if you’re not sure, you can ask your doctor if you should get a blood test to check your vitamin B12 level. The older you are, the harder it is to absorb the vitamin. If you have undergone weight loss surgery or had another operation that removed part of your stomach, or if you are a heavy alcohol drinker, it can affect your vitamin B12 level.

You may also be more likely to develop vitamin B12 deficiency if you have:

  • Atrophic gastritis, in which your stomach lining has thinned.
  • Pernicious anaemia, which makes it hard for your body to absorb vitamin B12
  • Conditions that affect your small intestine – such as Crohn’s disease, celiac disease, bacterial growth, or a parasite.
  • Alcohol misuse or heavy drinking can make it harder for your body to absorb nutrients or prevent you from eating enough calories. One sign that you lack enough B12 may be glossitis (a swollen or inflamed tongue).
  • Immune system disorders, such as Graves’ disease or Lupus.
  • Been taking certain medications that interfere with the absorption of B12. This includes some heartburn medicines, including proton pump inhibitors (PPIs) such as esomeprazole (Nexium), lansoprazole (Prevacid), omeprazole (Prilosec OTC), pantoprazole (Protonix), and rabeprazole (Aciphex), H2 Blockers such as cimetidine (Tagamet) and famotidine (Pepcid AC) and certain diabetes medicines such as metformin (Glucophage).

You can also get vitamin B12 deficiency if you follow a vegan diet (not eating animal products, including meat, milk, cheese, and eggs) or you are a vegetarian not eating enough eggs or dairy products to meet your vitamin B12 needs. In both of those cases, you can add fortified foods to your diet or take supplements to meet this need. 

How much vitamin B12 do you need?
According to WebMD[7], how much Vitamin B12 you need depends on your age, eating habits, medical conditions, and the medications you take. The average recommended amounts, measured in micrograms (mcg), vary by age:

  • Infants up to age six months: 0.4 mcg
  • Babies age 7-12 months: 0.5 mcg
  • Children age 1-3 years: 0.9 mcg
  • Kids age 4-8 years: 1.2 mcg
  • Children aged 9-13 years: 1.8 mcg
  • Teens age 14-18: 2.4 mcg (2.6 mcg per day if pregnant and 2.8 mcg per day if breastfeeding)
  • Adults: 2.4 mcg (2.6 mcg per day if pregnant and 2.8 mcg per day if breastfeeding)

You can get vitamin B12 in animal foods, which have it naturally, or from items that have been fortified with it. Animal sources include dairy products, eggs, fish, meat, and poultry. If you’re looking for a food that has been fortified with B12, you can check the Nutrition Facts label on the product.

Vitamin B12 shots are injections that a doctor may prescribe to treat a vitamin B12 deficiency, especially if a person’s body has difficulty absorbing the vitamin. If a person has low vitamin B12 levels due to a health condition, a doctor may recommend oral supplementation or injections of the vitamin.

Injections are usually for people with bodies that have problems absorbing vitamin B12 and those who have undergone gastric surgery. This is because injections enable the body to absorb vitamin B12 without going through the digestive system.

In animal-based foods, vitamin B12 binds to the protein molecules. During digestion, stomach acid causes it to separate from the protein, and a substance called intrinsic factor enables the bloodstream to absorb it. Some people’s bodies do not produce enough stomach acid or intrinsic factor if they have a condition known as autoimmune atrophic gastritis. These people may need vitamin B12 shots to reduce their risk of deficiency, which can lead to pernicious anaemia. Other people who may need injections include those who have had gastrointestinal surgery if their digestive system cannot absorb vitamin B12 efficiently.[8]

Symptoms of Vitamin B12 or Folate Deficiency[9]
If you have Vitamin B12 deficiency, you could become anaemic. A mild deficiency may cause no symptoms, but if untreated, it may lead to symptoms such as:

  • Weakness, tiredness, or lightheadedness
  • Heart palpitations and shortness of breath
  • Pale skin.
  • A smooth tongue.
  • Constipation, diarrhoea, loss of appetite, or flatulence. 
  • Nerve problems like numbness or tingling, muscle weakness, and problems walking.
  • Vision loss.
  • Mental problems like depression, memory loss, behavioural change, paranoia and delusions.
  • Incontinence.
  • Loss of taste and smell.

A deficiency in either vitamin B12 or folate can cause a wide range of problems, including:

  • Extreme tiredness.
  • A lack of energy.
  • Pins and needles (paraesthesia).
  • A sore and red tongue.
  • Mouth ulcers.
  • Muscle weakness.
  • Disturbed vision.
  • Psychological issues, which may include depression and confusion.
  • Problems with memory, understanding and judgement.

Some of these problems can still happen if you have a deficiency in vitamin B12 or folate but do not have anaemia.

If you have pernicious anaemia or have trouble absorbing vitamin B12, you’ll need injections 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 you don’t eat animal products, you have options. You can change your diet to include vitamin B12-fortified grains, a supplement or B12 injections, or a high-dose oral vitamin B12 if you have a deficiency.

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

For most people, treatment resolves the problem. But, any nerve damage that happened due to the deficiency could be permanent.

Preventing Vitamin B12 Deficiency
Eating enough meat, poultry, seafood, dairy products, and eggs will usually prevent a vitamin B12 deficiency. If you have a medical condition that limits how well your body can absorb nutrients, taking vitamin B12 in a multivitamin tablet or other supplement and foods fortified with vitamin B12 or having B12 injections every three months will be the way a deficiency is avoided.

Please note that if you choose to take vitamin B12 supplements, you should let your doctor know, so they can tell you how much you need to take, or ensure the supplements won’t affect any medicines you’re taking.

You should not use Vitamin B12 injection if you are allergic to cobalt or if you have Leber’s disease.

You should not use Vitamin B12 if you are allergic to cyanocobalamin or cobalt, or if you have Leber’s disease (an inherited form of vision loss). Cyanocobalamin can lead to optic nerve damage (and possibly blindness) in people with Leber’s disease.

To make sure this medicine is safe for you, tell your doctor if you have:

  • eye problems or Leber’s disease (in you or a family member)
  • kidney or liver disease
  • iron or folic acid deficiency
  • any type of infection or are receiving any medication or treatment that affects your bone marrow

You should avoid drinking large amounts of alcohol while being treated with Vitamin B12 injections.

Vitamin B12 side effects
You should get emergency medical help if you have signs of an allergic reaction to Vitamin B12: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

You should call your doctor at once if you experience:

  • Heart problems – swelling, rapid weight gain, feeling short of breath.
  • Fluid build-up in or around the lungs – pain when you breathe, feeling short of breath while lying down, wheezing, gasping for breath, cough with foamy mucus, cold and clammy skin, anxiety, rapid heartbeats; or
  • Low potassium levels – leg cramps, constipation, irregular heartbeats, fluttering in your chest, increased thirst or urination, numbness or tingling, muscle weakness or limp feeling.

Common vitamin B12 side effects may include:

  • diarrhoea; or
  • swelling anywhere in your body

Possible interactions with medications include:

  • Aminosalicylic acid (Paser). Taking this drug used to treat digestive problems might reduce your body’s ability to absorb vitamin B-12.
  • Colchicine (Colcrys, Mitigare, Gloperba). Taking this anti-inflammatory drug used to prevent and treat gout attacks might decrease your body’s ability to absorb vitamin B-12.
  • Metformin (Glumetza, Fortamet, others). Taking this diabetes drug might reduce your body’s ability to absorb vitamin B-12.
  • Proton pump inhibitors. Taking omeprazole (Prilosec), lansoprazole (Prevacid), or other stomach acid-reducing drugs might decrease your body’s ability to absorb vitamin B-12.
  • Vitamin C (ascorbic acid) supplements. Taking vitamin B-12 with vitamin C might reduce the available amount of vitamin B-12 in your body. To avoid this interaction, you should take vitamin C two or more hours after taking a vitamin B-12 supplement.

Your doctor might recommend changing drugs or timing doses to offset any potential interactions.

Caution: No advice is implied or given in articles published by us. This guide is for general interest only. It should never be used as a substitute for obtaining advice from your Doctor or other qualified clinician/medical practitioner. The facts are believed to be correct as at the date of publication, but there may be certain errors and omissions for which we cannot be responsible. The hyperlinks were valid at the date of publication. This paper mentions various side effects – it is not a complete list, and others may occur. Call your doctor for medical advice about side effects.

Sources and Further Reading

Picture Credit:doctor with patient 03” by bastamanography is marked with CC BY-NC-SA 2.0

  1. Source:

  2. Source:

  3. See: – Source: Thakkar K, Billa G (January 2015). “Treatment of vitamin B12 deficiency-methylcobalamine? Cyancobalamine? Hydroxocobalamin?-clearing the confusion”. European Journal of Clinical Nutrition. 69 (1): 1–2. doi:10.1038/ejcn.2014.165. PMID 25117994

  4. Source:

  5. Source: © Crown Copyright duly acknowledged

  6. Source:

  7. Ibid

  8. Source:

  9. Source: © Crown Copyright duly acknowledged

  10. Source and Credit:

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