Vitamin B12 is essential for red blood cell production, healthy nerve tissue and brain function.
The following are frequently asked questions about vitamin B12:
- What is vitamin B12?
- What are the main sources of vitamin B12?
- What causes vitamin B12 deficiency?
- Is there a blood test to detect vitamin B12 deficiency?
- Who needs vitamin B12 supplements?
- How is vitamin B12 deficiency treated?
Vitamin B12, also called cobalamin, belongs to the B vitamin group. Vitamin B12 is needed to make new cells in your body, such as red blood cells. It is important for normal blood and nerve function. It also plays a part in making folate (vitamin B9).
Making sure you get enough vitamin B12 is especially important during pregnancy and breastfeeding when more vitamin B12 is needed.
Most people get enough vitamin B12 from their diet. It is found in meat, fish, eggs, milk and milk products. It is generally not found in plant foods, but many processed foods have added vitamin B12, such as breakfast cereals.
Vegan dietary sources of vitamin B12 include fortified cereals, fortified non-dairy milk, nutritional yeast and Marmite.
Image credit: Canva
A lack of vitamin B12 leads to anaemia, low energy, stomach problems (constipation, loss of appetite, weight loss), poor memory and nerve damage. Symptoms include mouth ulcers, a sore and red tongue, feeling tired, pins and needles and changes in your vision.
The most common cause of vitamin B12 deficiency is pernicious anaemia. Some gut problems can also be a cause of vitamin B12 deficiency, eg:
- surgery to remove parts of your bowel (the stomach or the end of the small intestine)
- Crohn's disease
- atrophic gastritis (where the lining of the stomach is thinned)
- coeliac disease
- prolonged use of the medicines metformin or proton pump inhibitors (omeprazole, lansoprazole, pantoprazole).
Vitamin B12 deficiency due to diet
Vitamin B12 deficiency due to diet is not common, but can happen, eg, if you are on a long-term strict vegetarian or vegan (no animal products) diet. This is because vitamin B12 is generally not found in plant foods. There are some soy, rice, and nut milks that have B12 added. These are a readily available source of B12 for vegans and those who eat minimal animal products.
Chronic alcoholics are at risk of vitamin B12 deficiency because of poor nutrition.
Older people are also at risk of vitamin B12 deficiency because of reduced ability of your gut to absorb B12 from food as you get older.
Let your doctor know if you get symptoms of low vitamin B12. The level of vitamin B12 in your body can be measured by a blood test. They will check your vitamin B12 levels if you are in a high risk group or have symptoms of vitamin B12 deficiency.
Most healthy adults don't need vitamin B12 supplements. However, if you are at risk of vitamin B12 deficiency or have symptoms suggesting vitamin B12 deficiency, your doctor can check your vitamin B12 levels and prescribe a vitamin B12 supplement if your levels are low.
Treatment of vitamin B12 deficiency will depend on the cause. If your deficiency is due to your diet, you will need you to review your diet and include more vitamin B12 foods. People on a vegan diet may need to include more vitamin B12 fortified cereals, non-dairy milk, nutritional yeast and Marmite.
If the problem is due to poor absorption from your gut, or pernicious anaemia, your doctor may prescribe hydroxocobalamin, which is given as an injection, into your buttock muscle. Read more about vitamin B12 supplements.
- Food and nutrition guidelines Ministry of Health, NZ