How does vitamin B12 or folate deficiency cause anaemia?
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 can't 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 , which occurs when the body doesn't contain enough iron.
Symptoms of vitamin B12 or folate deficiency
Vitamin B12 and folate perform several important functions in the body, including keeping the nervous system healthy.
A deficiency in either of these vitamins 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 problems, which may include depression and confusion
- problems with memory, understanding and judgement
Some of these problems can also occur if you have a deficiency in vitamin B12 or folate, but don't have anaemia.
Read about the symptoms of vitamin B12 or folate deficiency anaemia .
When to see your doctor
See your doctor if you think you may have a vitamin B12 or folate deficiency. These 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 because, although many of the symptoms improve with treatment, some problems caused by the condition can be irreversible.
Read about diagnosing vitamin B12 or folate deficiency anaemia .
Causes of a vitamin B12 or folate deficiency
There are a number of problems that 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 – this is uncommon, but can occur if you have a vegan diet, follow a fad diet or have a generally poor diet for a long time
- medication – certain medications, 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.
Read about the causes of vitamin B12 or folate deficiency anaemia .
Treating vitamin B12 or folate deficiency anaemia
Most cases of vitamin B12 and folate deficiency 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 recurring. 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.
Read about treating vitamin B12 or folate deficiency .
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've 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 birth defects
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.
Read about the complications of vitamin B12 or folate deficiency anaemia .
What are the symptoms of vitamin B12 or folate deficiency?
Vitamin B12 or folate deficiency anaemia can cause a wide range of symptoms. These usually develop gradually but can worsen if the condition goes untreated.
Anaemia is where you have fewer red blood cells than normal or you have an abnormally low amount of a substance called haemoglobin in each red blood cell. General symptoms of anaemia may include:
- extreme tiredness (fatigue)
- lack of energy (lethargy)
- breathlessness
- feeling faint
- headaches
- pale skin
- noticeable heartbeats (palpitations)
- hearing sounds coming from inside the body, rather than from an outside source ( tinnitus )
- loss of appetite and weight loss
Vitamin B12 deficiency symptoms
If you have anaemia caused by a vitamin B12 deficiency, you may have other symptoms in addition to those listed above, such as:
- a pale yellow tinge to your skin
- a sore and red tongue (glossitis)
- mouth ulcers
- pins and needles (paraesthesia)
- changes in the way that you walk and move around
- disturbed vision
- irritability
- depression
- changes in the way you think, feel and behave
- a decline in your mental abilities, such as memory, understanding and judgement ( dementia )
Some of these symptoms can also occur in people who have a vitamin B12 deficiency, but have not developed anaemia.
Symptoms of folate deficiency
Additional symptoms in people with anaemia caused by a folate deficiency can include:
- symptoms related to anaemia
- reduced sense of taste
- diarrhoea
- numbness and tingling in the feet and hands
- muscle weakness
- depression
When to see your doctor
See your doctor if you're experiencing symptoms of vitamin B12 or folate deficiency anaemia. These conditions can often be diagnosed based on your symptoms and the results of a blood test.
Read more about diagnosing vitamin B12 or folate deficiency anaemia .
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 if left untreated. The longer the condition goes untreated, the higher the chance of permanent damage.
What are the causes of vitamin B12 or folate deficiency?
Vitamin B12 or folate deficiency anaemia occurs when a lack of either of these vitamins affects the body's ability to produce fully functioning red blood cells.
Red blood cells carry oxygen around the body. Most people with vitamin B12 or folate deficiency anaemia have underdeveloped red blood cells that are larger than normal. The medical term for this is "megaloblastic anaemia".
A vitamin B12 or folate deficiency can be the result of a variety of problems, some of which are described below.
Vitamin b12 deficiency causes
Pernicious anaemia
Pernicious anaemia is an autoimmune condition that affects your stomach. An autoimmune condition means your immune system (the body's natural defence system that protects against illness and infection) attacks your body's healthy cells.
In your stomach, vitamin B12 is combined with a protein called intrinsic factor. This mix of vitamin B12 and intrinsic factor is then absorbed into the body in part of the gut called the distal ileum.
Pernicious anaemia causes your immune system to attack the cells in your stomach that produce the intrinsic factor, which means your body is unable to absorb vitamin B12.
The exact cause of pernicious anaemia is unknown, but the condition is more common in women around 60 years of age, people with a family history of the condition and those with another autoimmune condition, such as Addison's disease or vitiligo .
Diet
Some people can develop a vitamin B12 deficiency as a result of not getting enough vitamin B12 from their diet.
A diet that includes meat, fish and dairy products usually provides enough vitamin B12, but people who don't regularly eat these foods – such as those following a vegan diet or who have a generally very poor diet – can become deficient.
Stores of vitamin B12 in the body can last around two to four years without being replenished, so it can take a long time for any problems to develop after a dietary change.
Conditions affecting the stomach
Some stomach conditions or stomach operations can prevent the absorption of enough vitamin B12.
For example, a gastrectomy (a surgical procedure where part of your stomach is removed) increases your risk of developing a vitamin B12 deficiency.
Conditions affecting the intestines
Some conditions that affect your intestines can also stop you from absorbing the necessary amount of vitamin B12.
For example, Crohn's disease (a long-term condition that causes inflammation of the lining of the digestive system) can sometimes mean your body doesn't get enough vitamin B12.
Medication
Some types of medicine can lead to a reduction in the amount of vitamin B12 in your body.
For example, proton pump inhibitors (PPIs) – a medication sometimes used to treat indigestion – can make a vitamin B12 deficiency worse. PPIs inhibit the production of stomach acid, which is needed to release vitamin B12 from the food you eat.
Your doctor will be aware of medicines that can affect your vitamin B12 levels and will monitor you if necessary.
Functional vitamin B12 deficiency
Some people can experience problems related to a vitamin B12 deficiency, despite appearing to have normal levels of vitamin B12 in their blood.
This can occur due to a problem known as functional vitamin B12 deficiency – where there's a problem with the proteins that help transport vitamin B12 between cells. This results in neurological complications involving the spinal cord.
Folate deficiency causes
Folate dissolves in water, which means your body is unable to store it for long periods of time. Your body's store of folate is usually enough to last four months. This means you need folate in your daily diet to ensure your body has sufficient stores of the vitamin.
Like vitamin B12 deficiency anaemia, folate deficiency anaemia can develop for a number of reasons. Some are described below.
Diet
Good sources of folate include broccoli, Brussels sprouts, asparagus, peas, chickpeas and brown rice. If you don't regularly eat these types of foods, you may develop a folate deficiency.
Folate deficiency caused by a lack of dietary folate is more common in people who have a generally unbalanced and unhealthy diet, people who regularly misuse alcohol and people following a fad diet that doesn't involve eating good sources of folate.
Malabsorption
Sometimes your body may be unable to absorb folate as effectively as it should. This is usually due to an underlying condition affecting your digestive system, such as coeliac disease .
Excessive urination
You may lose folate from your body if you urinate frequently. This can be caused by an underlying condition that affects one of your organs, such as:
- congestive heart failure – where the heart is unable to pump enough blood around the body
- acute liver damage – often caused by drinking excessive amounts of alcohol
- long-term dialysis – where a machine that replicates the kidney function is used to filter waste products from the blood
Medication
Some types of medicine reduce the amount of folate in your body, or make the folate harder to absorb.
These include some anticonvulsants (medication used to treat epilepsy ), colestyramine, sulfasalazine and methotrexate.
Your doctor will be aware of medicines that can affect your folate levels and will monitor you if necessary.
Other causes
Your body sometimes requires more folate than normal. This can cause folate deficiency if you can't meet your body's demands for the vitamin.
Your body may need more folate than usual if you:
- are pregnant (see below)
- have cancer
- have a blood disorder – such as sickle cell anaemia (an inherited blood disorder which causes red blood cells to develop abnormally)
- are fighting an infection or health condition that causes inflammation (redness and swelling)
Premature babies (born before the 37th week of pregnancy) are also more likely to develop a folate deficiency, because their developing bodies require higher amounts of folate than normal.
Pregnancy
If you're pregnant or trying to get pregnant, it's recommended that you take a 400 microgram folic acid tablet every day until you're 12 weeks pregnant. This will ensure that both you and your baby have enough folate and help your baby grow and develop.
Folic acid tablets are available with a prescription from your doctor, or you can buy them over the counter from pharmacies, large supermarkets and health food stores.
If you're pregnant and have another condition that may increase your body's need for folate, such as those mentioned above, your doctor will monitor you closely to prevent you from becoming anaemic.
In some cases, you may need a higher dose of folic acid. For example, if you have diabetes, you should take a 5 milligrams (5mg) supplement of folic acid instead of the standard 400 micrograms.
Read more about vitamins and nutrition in pregnancy .
How can I check if I have vitamin B12 or folate deficiency anaemia?
A diagnosis of vitamin B12 or folate deficiency anaemia can often be made by your doctor based on your symptoms and the results of blood tests .
Blood tests
Different types of blood tests can be carried out to help identify people with a possible vitamin B12 or folate deficiency. These tests check:
- whether you have a lower level of haemoglobin (a substance that transports oxygen) than normal
- whether your red blood cells are larger than normal
- the level of vitamin B12 in your blood
- the level of folate in your blood
However, some people can have problems with their normal levels of these vitamins or may have low levels despite having no symptoms. This is why it's important for your symptoms to be taken into account when a diagnosis is made.
A particular drawback of testing vitamin B12 levels is that the current widely-used blood test only measures the total amount of vitamin B12 in your blood.
This means it measures forms of vitamin B12 that are "active" and can be used by your body, as well as the "inactive" forms, which can't. If a significant amount of the vitamin B12 in your blood is "inactive", a blood test may show that you have normal B12 levels, even though your body can't use much of it.
There are some types of blood test that may help determine if the vitamin B12 in your blood can be used by your body, but these aren't yet widely available.
Identifying the cause
If your symptoms and blood test results suggest a vitamin B12 or folate deficiency, your doctor may arrange further tests. If the cause can be identified, it will help to determine the most appropriate treatment.
For example, you may have additional blood tests to check for a condition called pernicious anaemia. This is an autoimmune condition (where your immune system produces antibodies to attack healthy cells), which means you're unable to absorb vitamin B12 from the food you eat.
Tests for pernicious anaemia aren't always conclusive, but they can often give your doctor a good idea of whether you have the condition.
Referral to a specialist
You may be referred to a specialist for further tests or treatment. This may include:
- a haematologist (specialist in treating blood conditions) – if you have vitamin B12 or folate deficiency anaemia and your doctor is uncertain of the cause, you're pregnant or symptoms suggest your nervous system has been affected
- a gastroenterologist (specialist in conditions that affect the digestive system) – if your doctor suspects you don't have enough vitamin B12 or folate because your digestive system isn't absorbing it properly
- a dietitian (specialist in nutrition) – if your doctor suspects you have a vitamin B12 or folate deficiency caused by a poor diet
A dietitian can devise a personalised eating plan for you to increase the amount of vitamin B12 or folate in your diet.
Read our page on B vitamins and folic acid for information about good sources of these vitamins.
How are vitamin B12 or folate deficiency anaemia treated?
The treatment for vitamin B12 or folate deficiency anaemia will depend on what is causing the condition.
Different treatments are outlined below.
Vitamin B12 deficiency anaemia
Vitamin B12 deficiency anaemia is usually treated with injections of vitamin B12. The vitamin is in the form of a substance known as hydroxocobalamin.
At first you will have injections every other day for two weeks, or until your symptoms have stopped improving. Your doctor or nurse will give you the injections.
After the initial treatment, your dosage will depend on whether the cause of your vitamin B12 deficiency is related to your diet or not. The most common cause of vitamin B12 deficiency is pernicious anaemia.
Read more about the causes of vitamin B12 or folate deficiency.
Diet related
If your vitamin B12 deficiency is caused by a lack of the vitamin in your diet, you may be prescribed vitamin B12 tablets to take every day between meals. Alternatively, you may need to have an injection of hydroxocobalamin twice a year.
People who find it difficult to get enough vitamin B12 in their diets, such as vegans (people whose diet only contains food from plants), may need vitamin B12 tablets for life. People with vitamin B12 deficiency caused by a poor diet over a long period of time may have their tablets stopped by their doctor once their vitamin B12 levels have returned to normal and their diet has improved. However, it is rarer for a non-vegan to experience vitamin B12 deficiency.
Good sources of vitamin B12 include:
- meat
- salmon
- milk
- eggs
If you are a vegetarian or vegan, or are looking for alternatives to meat and dairy products, there are other foods that contain vitamin B12, such as:
- some fortified breakfast cereals
- some soy products
You can check the nutritional labels of these foods to see how much vitamin B12 they contain.
Read more information about good sources of B vitamins and folates.
Not diet related
If your vitamin B12 deficiency is not caused by a lack of vitamin B12 in your diet, you will usually need to have an injection of hydroxocobalamin every three months for the rest of your life.
If you have had neurological symptoms (symptoms that affect your nervous system, such as an altered sense of touch) because of vitamin B12 deficiency, you will be referred to a haematologist (a doctor who specialises in blood conditions). You may need to have injections every two months. Your haematologist will advise on how long you need to keep taking the injections.
If you need replacement injections of vitamin B12, hydroxocobalamin is preferred to cyanocobalamin in the UK. This is because hydroxocobalamin stays in the body longer.
If you need regular injections of vitamin B12, cyanocobalamin will need to be given once a month, while hydroxocobalamin can be given every three months.
Read more about [hydroxocobalamin] and [cyanocobalamin].
Folate deficiency anaemia
To treat folate deficiency anaemia, your doctor will usually prescribe daily folic acid tablets to build up your folate levels. They may also give you dietary advice so you can increase your folate intake.
Most people will need to take folic acid tablets for about four months. However, if the underlying cause of your folate deficiency anaemia is persistent, you may have to take folic acid tablets for longer, and maybe for life.
Before you start taking folic acid, your doctor will check your vitamin B12 levels to make sure they are normal. This is because folic acid treatment can sometimes improve your symptoms so much that it masks an underlying vitamin B12 deficiency. If a vitamin B12 deficiency is not detected and treated, it could affect your nervous system (brain, nerves and spinal cord).
Monitoring your condition
To ensure your treatment is working, your vitamin B12 or folate levels will need to be closely monitored.
Around 10 days after starting treatment, you will need a blood test to check your vitamin B12 or folate levels are starting to rise. You will need another blood test after approximately eight weeks to confirm your treatment has been successful.
If you have been taking folic acid tablets, you may be tested again once the treatment has finished (usually after four months).
Most people who have had a vitamin B12 or folate deficiency will not need further monitoring unless their symptoms return, or their treatment is ineffective. If your doctor feels it is necessary, you may have to return for an annual blood test to see whether your condition has returned.
Complications of vitamin B12 or folate deficiency
As most cases of vitamin B12 deficiency or folate deficiency can be easily and effectively treated, complications are relatively rare.
However, in some cases complications can develop, particularly if you have been deficient in vitamin B12 or folate for some time.
Anaemia complications
Anaemia, regardless of what it is caused by, can lead to heart and lung complications as the heart struggles to pump oxygen to the vital organs.
Adults with severe anaemia are at risk of developing:
- tachycardia – an abnormally fast heart beat
- heart failure – where your heart does not pump blood around your body very efficiently
Vitamin B12 deficiency complications
A lack of vitamin B12 can cause the following complications:
Nervous system
A lack of vitamin B12 can affect your nervous system (the brain, nerves and spinal cord). For example, you may experience:
- vision problems
- memory loss
- paraesthesia (pins and needles) – a prickling or tingling feeling in the arms, legs, hands or feet
- ataxia – the loss of physical coordination, which can affect your whole body and cause difficulty speaking or walking
Fertility
Vitamin B12 deficiency can sometimes lead to temporary infertility (an inability to conceive).
Neural tube defects
If you are pregnant, not having enough vitamin B12 can increase the risk of your baby developing a neural tube defect. Neural tube defects affect your baby's growth and development. Examples of neural tube defects include:
- spina bifida – where the baby's spine does not develop properly
- anencephaly – where the baby's brain and skull bones do not develop properly
Folate deficiency complications
A lack of folate can cause complications, some of which are outlined below.
Fertility
As with a lack of vitamin B12, a folate deficiency can also affect your fertility. However, effects are only temporary and can be reversed by using vitamin supplements.
Cardiovascular disease
Research has shown a lack of folate in your body may increase your risk of cardiovascular disease. Cardiovascular disease is a term that describes a number of health conditions that affect:
- your heart
- your blood vessels
- the way blood circulates (flows) around your body
Cancer
Research has shown folate deficiency can be linked to some cancers, such as stomach cancer. A lack of folate is never the sole cause of a cancer developing, but it may be a contributory factor.
Neural tube defects
As with a vitamin B12 deficiency, a lack of folate can also affect your baby's growth and development in the womb (uterus). This increases the risk of neural tube defects developing in the unborn baby, such as spina bifida.
Premature birth
As well as affecting your baby's growth, a lack of folate during your pregnancy may also increase the risk of your baby being born prematurely (before week 37 of the pregnancy).
