Vitamin B12 is an important vitamin that the body requires in order to remain healthy for a host of reasons including brain function and the production of red blood cells.
Dr Roger Henderson looks at why Vitamin B12 is so important, the symptoms of B12 deficiency and how to ensure you hit your daily quota:
What is vitamin B12?
Vitamin B12 – sometimes also known as cobalamin – is a water-soluble vitamin that is essential for good health. It plays a vital role in making new red blood cells and DNA, and ensuring that our nervous system remains healthy. It also helps prevent tiredness and fatigue, and supports our immune system.
Vitamin B12 is not found in fruit or vegetables but is naturally found in animal foods including fish, meat, eggs, dairy and poultry. It can also be found in vitamin B12-fortified products such as bread, some cereals and plant-based milk.
Vitamin B12 deficiency causes
B12 deficiency can be quite common, especially in the elderly. The risk is significantly increased if you don’t get enough vitamin B12 from your diet, or you are unable to absorb enough from the food you eat. Common vitamin B12 deficiency causes include:
• Pernicious anaemia
Pernicious anaemia is the commonest cause of B12 deficiency in the UK, and is classified as an autoimmune condition. When we eat foods containing vitamin B12, the B12 combines with a protein called intrinsic factor which is made in the stomach. This combination then travels lower down the small intestine where it is absorbed into the body.
In pernicious anaemia, the body makes antibodies against the intrinsic factor and the cells that manufacture it. This prevents it from attaching to vitamin B12 and so the body is unable to absorb any B12. The exact reason why this occurs is unclear but pernicious anaemia is more common over the age of 50, in women, and if there is a family history of it. It is also more likely to occur in people who have another autoimmune condition such as Addison’s disease, rheumatoid arthritis and some thyroid problems.
Some drugs can slow down or block the absorption of vitamin B12. The two most commonly taken here are antacids such as proton pump inhibitors and H2 blockers – these reduce stomach acid levels, and this is needed to help release B12 in food – and metformin, which is the most commonly prescribed drug for diabetes. Other drugs which have been linked to the absorption of B12 include some anti-epilepsy treatments, colchicine (used to treat gout) and the antibiotic neomycin. Women who take the oral contraceptive pill long-term may also be at a slight risk but this is less than with other drugs that can affect B12 levels.
People following a strict vegan diet can suffer from low levels of B12 but it is unusual to be affected if you eat a normal balanced diet (around 1-2% of the UK population eat a strictly animal-free diet).
• Stomach problems
People who have had surgery to remove the part of the bowel that absorbs B12 typically suffer from B12 deficiency, as can people with gut problems that affect B12 absorption. These include inflammatory bowel problems such as Crohn’s disease, and atrophic gastritis where the lining of the stomach wall becomes very thin. People with the stomach bug H. Pylori can also be B12 deficient.
Vitamin B12 deficiency symptoms
Common vitamin B12 deficiency symptoms are linked to anaemia and include:
Tiredness and unexplained fatigue
Shortness of breath
Ringing in the ears (tinnitus)
Symptoms of pernicious anaemia include mouth ulcers, a sore tongue and cracking to the sides of the mouth. Others may be pins and needles in the hands and feet, problems with vision, mood changes and a lemon-coloured tinge to the skin.
Vitamin B12 plays an important role in producing myelin – the insulating material that surrounds the nerves. Vitamin B12 deficiency can therefore affect this and cause pins and needles or a prickling sensation in the hands and feet.
Vitamin B12 deficiency diagnosis
Vitamin B12 deficiency diagnosis is done with a simple blood test that measures the level of B12 in the blood. If the level is low, further blood tests can then be done to find out if pernicious anaemia is the cause – these are tests for antibodies to gastric parietal cells and intrinsic factor. You may also have a Schilling test, which uses a radioactive form of B12 to see if your body has enough intrinsic factor.
Vitamin B12 deficiency treatment
The usual treatment for vitamin B12 deficiency is with injections of B12 that are initially given frequently to build up the body’s store of the vitamin, and then the frequency is slowly reduced to maintenance injections every two to three months to keep the supply topped up. These injections are needed for life but if the deficiency is due to a simple dietary insufficiency then a dietary supplement of B12 may be all that is needed rather than injections.
The recommended vitamin B12 dosage in pernicious anaemia depends on whether nerve problems are present or not. If they are not then the injections are initially three times a week for two weeks and then one every three months. If they are, then these are more frequent – typically one injection three times a week until there is no further improvement in symptoms, and then one every two months.
Although the usual long-term treatment regimen is one injection every three months, there are some patients with B12 deficiency that report the treatment benefit wears off before this time and so may need slightly more frequent treatments.
If dietary supplementation is required, there is no known advantage in taking more than the recommended dose of 1.5 micrograms per day. As B12 is water-soluble, overdose by taking too much is not a risk as the body simply excretes any excess and doesn’t store it in the body.
To increase the amount of vitamin B12 in your diet, eat more B12-rich foods such as red meat, fish and shellfish, fortified breakfast cereals, low-fat milk, yogurt, cheese and eggs.
Vitamin B12 deficiency follow-up
For most people needing B12 treatment, anaemia symptoms tend to improve quickly once treatment has been started. A yearly blood test is usual to make sure that the vitamin level remains normal, and other tests are usually done at the same time such as a full blood count, folate level and thyroid function (thyroid problems are slightly more common in people with pernicious anaemia). If nerve damage has occurred due to chronic vitamin B12 deficiency this can be harder to treat, and may not fully recover with treatment.
Pernicious anaemia raises the risk of developing cancer of the stomach – you are about three times more likely to develop it compared to someone who does not have it, even when the anaemia has been treated – so always report any stomach symptoms such as indigestion, pain or weight loss to your GP if you have been diagnosed with pernicious anaemia.
Last updated: 11-03-2021
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