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 red blood cells that are underdeveloped and 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

Pernicious anaemia

Pernicious anaemia is the most common cause of vitamin B12 deficiency in the UK.

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.

Vitamin B12 is absorbed into your body through your stomach. A protein called "intrinsic factor" attaches itself to vitamin B12, so it can be absorbed from the food you eat.

Pernicious anaemia causes your immune system to attack the cells in your stomach that produce the intrinsic factor, which means your body in 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 does not getting 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 GP will be aware of medicines that can affect your vitamin B12 levels, and will monitor you if they think it is 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 is a problem with the proteins that help transport vitamin B12 between cells. This results in neurological complications involving the spinal cord.

Folate deficiency

Folate is a water-soluble vitamin (it 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 GP will be aware of medicines that can affect your folate levels, and will monitor you if they feel it is necessary.

Other causes

Your body sometimes requires more folate than normal. This can cause folate deficiency if you cannot 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 are pregnant or trying to get pregnant, it is recommended that you take a 400 microgram folic acid tablet every day until you are 12 weeks pregnant. This will ensure that both you and your baby have enough folate, and will help your baby grow and develop.

Folic acid tablets are available with a prescription from your GP, or you can buy them over the counter from pharmacies, large supermarkets and health food stores.

If you are pregnant and have another condition that may increase your body's need for folate, such as those mentioned above, your GP 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.