Vitamin B12 deficiency: causes, symptoms and who is at risk

1. Introduction

Vitamin B12, also called cobalamin, is a nutrient that helps keep blood cells and nerve cells healthy and is needed to make DNA, the body's genetic material ^[2]. The body cannot make it, so it must come from food or supplements ^[3]. When there is not enough, a person can develop a form of anaemia, which means too few healthy red blood cells, as well as nerve and brain symptoms ^{[1, 3]}. This article explains the causes, symptoms, tests and care, using information from the NHS, the US National Institutes of Health and the US National Heart, Lung, and Blood Institute.

2. Food sources

B12 occurs naturally in animal foods such as meat, fish, poultry, eggs, milk and dairy products ^{[1, 2]}. Plant foods contain no B12 unless it has been added, for example in some breakfast cereals, plant-based milks and nutritional yeast ^{[2, 3]}. Because of this, people who follow a vegan diet are at risk of low levels unless they use fortified foods or supplements ^{[1, 2]}.

3. Causes and risk factors

Low B12 is more often caused by problems absorbing the vitamin than by a poor diet, which the NHS describes as an uncommon cause ^[1]. Important causes and risk groups include ^{[1, 2, 3]}:

• Pernicious anaemia. An autoimmune condition, in which the immune system attacks cells in the stomach, so the body cannot make a protein called intrinsic factor that is needed to absorb B12. The NHS describes it as the most common cause of B12 deficiency in the United Kingdom ^[1].
• Older age. Many older adults make less stomach acid and absorb B12 from food poorly. The NHS reports that roughly 1 in 10 people aged 75 and over are affected ^[1].
• Stomach or bowel surgery, including weight-loss surgery.
• Digestive conditions such as coeliac disease and Crohn's disease.
• Some medicines, including acid-reducing medicines, some anti-seizure medicines and metformin, a diabetes medicine, which may lower absorption over time ^{[1, 2, 3]}.
• Heavy alcohol use, which reduces absorption ^[3].
• A vegan or very restricted diet without fortified foods or supplements ^{[1, 2]}.

Pregnant or breastfeeding women who are strict vegetarians or vegans may pass a shortage to their baby ^[2].

4. Signs and symptoms

The body stores a large amount of B12, so symptoms may take years to appear ^[2]. Symptoms described by the sources include ^{[1, 2, 3]}:

• Extreme tiredness, weakness and paleness
• Shortness of breath, dizziness or headaches
• Pins and needles or numbness in the hands and feet
• A sore, red tongue and mouth ulcers
• Problems with balance or walking
• Low mood, anxiety, confusion, memory problems
• Vision problems

Nerve damage can occur even without anaemia ^[2]. In babies, low B12 can cause poor growth and delayed development ^[2].

5. Diagnosis and tests

Doctors usually diagnose B12 deficiency from symptoms and blood tests ^[1]. A complete blood count checks the red blood cells and haemoglobin, and a separate test measures the level of B12 in the blood ^[3]. NHLBI notes that a normal B12 level does not always rule out deficiency, so your doctor may do more tests to find the cause ^[3].

6. Treatment and prevention

Treatment depends on the cause, and your doctor decides what is right for you. The NHS says B12 deficiency is usually easily treated with injections or tablets, often starting with injections, and that some people need treatment for life ^[1]. NHLBI adds that B12 can also be given by nasal spray, and that serious cases may need B12 injections until levels return to normal and sometimes blood transfusions ^[3]. Symptoms may take months to improve, and nerve symptoms such as numbness can sometimes persist ^[3].

Eating B12-rich foods, such as meat, fish, eggs, dairy and fortified products, helps reduce the chance of the problem returning ^{[1, 3]}. The NIH advises adults over 50 to get most of their B12 from fortified foods or supplements, because absorption from food falls with age ^[2]. NIH also notes that B12 supplements have not been shown to boost energy in people who already get enough ^[2].

7. Possible complications

Complications are uncommon and become more likely after a long period of deficiency. The NHS lists nervous system problems, heart conditions and, in pregnancy, complications and birth defects ^[1]. Some of these effects, especially to the nerves, can be permanent even after treatment starts, which is why a delay in seeking help can matter ^{[1, 2]}.

NHLBI adds that untreated deficiency can lead to bleeding, infections and permanent brain or nerve problems, and that babies born to mothers with B12 deficiency may have developmental delays ^[3]. The NHS adds that adults with severe anaemia may develop heart failure ^[1]. This is why early diagnosis matters.

Folate, also called vitamin B9, is closely linked with B12, and a shortage of either can cause a similar type of anaemia in which the body makes unusually large red blood cells that do not work properly. The NHS notes that folate is found in green vegetables such as broccoli, Brussels sprouts and peas ^[1]. Because the two can look alike, your doctor will use blood tests to find out which is involved.

8. When to see a doctor

See a doctor if you think you may be low in B12, particularly if you have tingling, numbness, balance problems or memory changes, if you are vegan or vegetarian, if you are older, or if you take a medicine that can lower absorption ^{[1, 2]}. Do not stop a prescribed medicine yourself. Tell your doctor about every medicine and supplement you take.

In an emergency, call your local emergency number (112 in India, 911 in the United States).

9. Conclusion

B12 deficiency is common in older adults and in people with absorption problems or a diet without animal foods or fortified products. Symptoms can build slowly, and delays can leave lasting nerve damage, so a blood test and medical advice are the right first step.