Vitamin B12 Explained: How Much You Need, Food Sources, and Who May Be at Risk

Vitamin B12 does a lot of quiet but essential work in the body, from making red blood cells to keeping your nervous system healthy. Most people who eat animal foods get enough from their diet, but some groups are more likely to run low, sometimes without realizing it for years.

This guide explains what vitamin B12 does, how much you need, where to get it, who may be at risk of low levels, the possible signs of deficiency, and what to know about B12 supplements.

This article is for general educational purposes and is not medical advice. Please see our medical disclaimer.

What Does Vitamin B12 Do?

According to the NHS, vitamin B12 is involved in helping the body:

• make red blood cells and keep the nervous system healthy;
• release energy from food;
• use folate, another B vitamin.

A lack of vitamin B12 can lead to a type of anemia called vitamin B12 deficiency anemia, in which the body produces abnormally large red blood cells that cannot work properly.

How Much Vitamin B12 Do You Need?

Recommendations differ a little between countries:

• UK: the NHS says adults aged 19 to 64 need about 1.5 micrograms (mcg) a day.
• US: Harvard's Nutrition Source notes that the Recommended Dietary Allowance for men and women aged 14 and older is 2.4 mcg a day.

These are small amounts. The NHS notes that if you eat meat, fish, or dairy foods, you should be able to get enough vitamin B12 from your diet. Because B12 is not found naturally in foods such as fruit, vegetables, and grains, people following a vegan diet may not get enough.

Where to Get Vitamin B12

Vitamin B12 is found naturally in animal foods. Harvard and the NHS list good sources including:

• fish and shellfish;
• meat and poultry;
• eggs;
• milk, cheese, and yogurt;
• fortified breakfast cereals;
• fortified nutritional yeast and enriched soy or rice milk.

If you eat mostly plant foods, fortified foods are especially important, since plants do not naturally provide reliable amounts of B12. Our guide on how much protein you need also covers balanced plant and animal protein sources.

Who May Be at Risk of Low B12?

Some people find it harder to get enough vitamin B12 from food, or to absorb it:

• People who follow a vegan or vegetarian diet. Harvard advises that vegetarians and vegans include B12-fortified foods or a B12 supplement. This is particularly important during pregnancy, since the baby needs B12 for healthy nervous system development.
• Adults over 50. Stomach acid is needed to release B12 from food. Harvard estimates that 10% to 30% of adults over 50 have difficulty absorbing vitamin B12 from food. The NHS also notes that it becomes more difficult to absorb B12 as you get older.
• People taking acid-reducing medicines. Harvard notes that proton-pump inhibitors, H2 blockers, and other antacids used for reflux or ulcers may make it harder to absorb B12 from food.
• Long-term metformin users. According to Harvard, long-term use of metformin, a common type 2 diabetes medicine, is strongly associated with vitamin B12 deficiency.
• People with pernicious anemia. This autoimmune condition affects the stomach so that the body cannot make enough intrinsic factor, a protein needed to absorb B12.

If you are in one of these groups, do not stop any medicine on your own. Ask your doctor whether your B12 levels should be checked.

Possible Signs of Low Vitamin B12

The NHS lists several symptoms of vitamin B12 or folate deficiency anemia, including:

• feeling weak or tired;
• shortness of breath and headaches;
• loss of appetite and indigestion;
• palpitations;
• a sore or red tongue, sometimes with mouth ulcers;
• problems with memory, understanding, and judgment.

Vitamin B12 deficiency can also cause symptoms that affect the brain and nervous system, such as pins and needles, numbness, muscle weakness, problems with balance and coordination, and psychological changes ranging from low mood to confusion.

Many of these symptoms have other possible causes, so they are not a reason to self-diagnose. The NHS advises seeing a doctor if you have symptoms, since a deficiency can often be diagnosed with your symptoms and a blood test. It also stresses that early treatment matters, because some problems caused by the condition can become permanent if left untreated.

What About B12 Supplements?

B12 supplements and fortified foods contain B12 in a free form that may be more easily absorbed than the B12 in animal foods, according to Harvard. A few points are worth knowing:

• Form doesn't matter much for most people. Harvard notes that claims about sublingual tablets or liquids having better absorption have not been shown to make an important difference.
• High doses are not always absorbed. B12 tablets often contain amounts far above the recommended intake, but how much is absorbed also depends on intrinsic factor.
• Some people need treatment from a doctor. In pernicious anemia, a high-dose supplement may not solve the problem, because the body cannot absorb B12 properly. A doctor can recommend the right treatment. The NHS notes that vitamin B12 deficiency anemia is usually treated with B12 injections.
• Safety. Harvard notes that no upper limit has been set for vitamin B12, as there is no established toxic level. The NHS is more cautious, saying there is not enough evidence on the effects of high daily doses, and that taking 2 mg or less a day in supplements is unlikely to cause any harm. It is wise to check with a pharmacist or doctor before starting any supplement, especially if you take other medicines.

The NHS also warns that taking high doses of folic acid can mask the symptoms of vitamin B12 deficiency, which can eventually damage the nervous system if it is not spotted and treated. This is another reason to get advice before taking high-dose supplements.

For other common supplements, see our guides to vitamin D, magnesium, and omega-3s.

My Take

What surprised me most while researching B12 is that deficiency is not only about diet. Age, stomach acid, and some very common medicines can all affect how well B12 is absorbed, even in people who eat plenty of animal foods. If you are vegan, over 50, or on long-term reflux or diabetes medicine, a simple conversation with your doctor about checking your B12 seems like a sensible step rather than guessing with supplements.

Frequently Asked Questions

How much vitamin B12 do I need a day?

The NHS says adults need about 1.5 mcg a day, while the US recommendation for ages 14 and older is 2.4 mcg a day.

Do vegans need a B12 supplement?

People following a vegan diet should include B12-fortified foods or a B12 supplement, since plant foods do not naturally provide reliable amounts.

Can you take too much vitamin B12?

No upper limit has been set in the US because there is no established toxic level. The NHS says 2 mg or less a day from supplements is unlikely to cause harm. It is still best to talk with a health professional before taking high-dose supplements.

Is sublingual B12 better than tablets?

Studies have not shown an important difference in absorption between sublingual forms and regular tablets, according to Harvard.

How do I know if I am low in B12?

Symptoms such as tiredness, pins and needles, or a sore tongue can have many causes. A doctor can assess your symptoms and arrange a blood test if needed.

The Bottom Line

Vitamin B12 helps make red blood cells, supports the nervous system, and helps release energy from food. Adults need only small amounts, which most people get from animal foods or fortified foods.

Vegans and vegetarians, adults over 50, and people taking acid-reducing medicines or metformin are more likely to run low. If you have symptoms or are in a higher-risk group, talk with your doctor rather than guessing, since early diagnosis and treatment matter.

Sources

• NHS: Vitamin B
• NHS: Vitamin B12 or folate deficiency anaemia
• Harvard T.H. Chan School of Public Health, The Nutrition Source: Vitamin B12