What to know about vitamin B12 deficiency and how to check your levels

What is vitamin B12?

Vitamin B12, also called cobalamin, is a nutrient that humans get from food. It's essential for:

• red blood cell production
• DNA synthesis
• a healthy nervous system

Vitamin B12 is also important for a healthy heart and during pregnancy.

Your body stores B12 away in your liver. When your levels are good, these stores can last for years.

What is vitamin B12 deficiency?

Vitamin B12 deficiency means your B12 levels are running low. To begin with, this doesn't always cause symptoms. Because of how much B12 the liver stores, it can take a long time for the symptoms of a deficiency to develop.

When a deficiency does start to affect the body, it may cause:

Anaemia

Anaemia is a condition where red blood cells can't carry oxygen to your cells efficiently.

In B12 deficiency, this happens because the cells are too big or underdeveloped to work properly. Some people also have low white blood cells, which help fight infections, or platelets, which help the blood to clot.

Psychological symptoms

Vitamin B12 helps your body make brain chemicals that regulate your mood, motivation, and concentration.

A lack of B12 might cause you to feel down, depressed, or anxious.

Neurological symptoms

Without treatment, severe B12 deficiencies can affect the nerves. This is because vitamin B12 helps to make myelin, the protective sheath that covers the nerves.

Without this sheath, people can have difficulty with balance, movement, memory, or their vision. Sometimes, the symptoms can mimic dementia.

Prompt treatment can rebuild the myelin, but this can take time. Rarely, people have long-term complications, which is why it's important to get a B12 test as soon as possible if you have any concerns.

Symptoms of vitamin B12 deficiency

B12 deficiency can cause a wide range of symptoms. If a lack of B12 causes anaemia, you might experience:

• tiredness
• weakness
• dizziness
• heart palpitations
• pale skin
• a red or sore tongue (glossitis)

If B12 deficiency affects the nervous system, it can cause:

• tingling in the hands and feet
• difficulty thinking or remembering
• problems with balance or movement
• changes in smell or taste
• mood changes, such as depression
• blurred vision
• unexplained weight loss

B12 deficiency can also affect fertility and pregnancy health.

But not everyone with a B12 deficiency will have all these symptoms. In fact, a 2017 study says that it's uncommon for people to have both anaemia and neurological symptoms from B12 deficiency.

What is more common is a subclinical deficiency, where levels are low but not severe. The researchers estimate that this may affect between 2.5% and 26% of the population, depending on how it's defined.

Causes of vitamin B12 deficiency

Several things can cause vitamin B12 deficiency, including:

• Diet: Vitamin B12 is almost exclusively in animal products, such as meat and eggs, as well as some fortified foods. If you don't eat many of these, you may not get enough B12 from food alone.
• Autoimmune gastritis: This condition occurs when your immune system attacks cells in your stomach that produce intrinsic factor, a protein you need to absorb vitamin B12. Over time, this can lead to pernicious anaemia.
• Coeliac disease: This autoimmune condition causes symptoms if a person eats gluten, which is a protein in wheat, barley, and rye. Coeliac disease can also cause problems with absorbing B12.
• Digestive conditions: Several digestive conditions can interfere with B12 absorption, such as Crohn's disease.
• Some medications: Drugs like proton pump inhibitors and H2 blockers reduce stomach acid, which can inhibit the absorption of vitamin B12.
• Surgery: Some surgeries remove parts of the stomach and small intestine that help to process B12.

You're also more at risk of vitamin B12 deficiency if you:

• are pregnant or breastfeeding
• are an older adult, as some people produce less stomach acid as they age
• consume a lot of alcohol
• use nitrous oxide

How to test your vitamin B12 levels

There are several tests a doctor might suggest if you have signs of a B12 deficiency:

• total B12 test, which tests the total amount of B12 currently in your blood
• an active B12 test, which measures the B12 your body can actually use
• a complete blood count, which can look for signs of anaemia
• biomarkers such as methylmalonic acid (MMA) and homocysteine, which rise when B12 is low
• intrinsic factor antibodies, which can reveal if you have autoimmune gastritis

The best way to check your vitamin B12 levels are through a blood test. Learn more about getting started with Thriva's home blood tests.

Be aware that some factors can interfere with how accurate blood tests are. For example, the National Institute for Health and Care Excellence (NICE) says that taking a B12 supplement can alter blood test results, making your levels appear healthy without fully treating a deficiency.

Taking folate or folic acid can also mask some B12 deficiency symptoms.

If you think you might have a B12 deficiency, try to get a test before you start taking any supplements, if possible.

How to treat vitamin B12 deficiency

The treatment for B12 deficiency depends on several factors, including:

• how low your levels are
• how severe your symptoms are
• what caused the deficiency, if known

If you have a mild, reversible form of B12 deficiency, a doctor may recommend eating more B12-rich foods or taking a supplement to rebuild your body's stores.

But if you have very low levels of B12, neurological symptoms, or a condition that prevents B12 absorption, your doctor will recommend B12 injections.

B12 injections deliver a higher dose of B12 more quickly than tablets can. They also bypass any digestive conditions.

If you need injections, doctors will often start by giving several over a few days. They will then keep giving injections spaced further apart until your symptoms get better. This can take up to three months.

Blood tests for B12 will look normal, or even very high, during and after treatment. This can be a temporary effect of the injections or supplements, which is why NICE recommends that doctors base the number and frequency of injections on your symptoms, not on blood test results.

In some cases, people need regular top-up injections or to take a daily supplement to maintain healthy B12 levels.

B12 food sources

Foods rich in vitamin B12 include:

• organ meats, such as liver and kidney
• beef
• seafood and fish, such as clams, sardines, salmon, and tuna
• milk and dairy products
• eggs

Natural B12 only occurs in meat, fish, or dairy. But there are fortified plant-based sources of vitamin B12, such as:

• fortified milk alternatives
• fortified cereals
• fortified nutritional yeast

Takeaway

Vitamin B12 is an essential nutrient for your health, supporting energy, mood, and many other functions.

If you're worried you might not be getting enough, it's worth looking into as soon as you can. B12 deficiency is very treatable, but it's always better to spot it early.