Vitamin B12 keeps your blood and nerve cells healthy and helps make DNA. Most people in the U.S. get enough from food, but some groups, including vegetarian and vegan moms and their breastfed babies, are at real risk of running low.

The short version

  • Common symptoms: tiredness, weakness, pale skin, a racing heart, numb or tingly hands and feet, balance problems, memory trouble, low mood, and a sore mouth or tongue.
  • Slow to show up: your body stores a large supply, so symptoms can take several years to appear, according to the NIH.
  • Who’s at risk: vegetarians and vegans, people over 50, people with certain stomach or digestive conditions or weight-loss surgery, and people taking metformin or acid-reducing medicines long term.
  • For moms: if you’re vegetarian or vegan while pregnant or breastfeeding, your baby can also run low.
  • The link to folate: B12 and folate deficiency cause the same type of anemia, and high folic acid intake can hide B12 deficiency while nerve damage continues.

Symptoms of B12 deficiency

Symptoms fall into two groups: those from anemia and those from nerve damage. The NIH lists:

From anemia (megaloblastic anemia)

  • Tiredness and weakness
  • Pale skin
  • Heart palpitations
  • Loss of appetite and weight loss

From nerve and brain effects

  • Numbness or tingling in the hands and feet
  • Problems with balance
  • Confusion and poor memory
  • Depression

Other signs

  • A sore mouth or tongue
  • Infertility

In babies, signs include failure to thrive (not growing or gaining weight as expected), delays in reaching developmental milestones, and anemia.

The nerve damage matters most. B12 deficiency can damage the nervous system even in people who don’t have anemia, so it’s important to treat it as soon as it’s found.

Who’s at risk

B12 deficiency usually comes from one of two problems: not getting enough in your diet, or not absorbing it. Your body absorbs B12 from food in two steps. Stomach acid frees it from protein, then it binds to a protein your stomach makes, called intrinsic factor. Anything that interferes with either step raises the risk, according to the NIH.

Group Why they may run low
Vegetarians and vegans B12 is found naturally only in animal foods.
Babies of vegetarian or vegan moms When pregnant or breastfeeding women are strict vegetarians or vegans, their babies may not get enough B12.
Adults over 50 Many make less stomach acid, so they absorb less B12 from food. B12 deficiency affects 3% to 43% of older adults.
People with pernicious anemia This autoimmune condition stops the body from making intrinsic factor.
People who’ve had weight-loss surgery or other stomach or intestinal surgery They may make less stomach acid and intrinsic factor.
People with celiac disease or Crohn’s disease These conditions can interfere with absorption.
People taking metformin This diabetes and prediabetes medicine may lower B12 absorption and blood levels.
People taking acid-reducing medicines long term Medicines for reflux and ulcers, such as omeprazole and lansoprazole, slow the stomach acid needed to free B12 from food.

What this means for moms

If you eat little or no animal food and you’re pregnant, planning a pregnancy, or breastfeeding, talk with your provider about B12. Your needs go up during pregnancy and breastfeeding, and your baby depends on your supply. A reliable source such as fortified foods or a supplement protects both of you. If you take metformin, ask whether your B12 should be checked.

How much B12 you need, and where to get it

Daily needs are small and measured in micrograms (mcg), according to the NIH:

Age or stage Daily amount (mcg)
Birth to 6 months 0.4
7 to 12 months 0.5
1 to 3 years 0.9
4 to 8 years 1.2
9 to 13 years 1.8
Teens and adults 2.4
Pregnant 2.6
Breastfeeding 2.8

Food sources. Fish, meat, poultry, eggs, milk, and other dairy products all contain B12. Clams, oysters, and beef liver are among the richest sources. (If you’re pregnant, see our foods guide for why liver needs caution.)

For plant-based diets. Plant foods have no B12 unless it’s added. Some breakfast cereals, nutritional yeasts, and other foods are fortified; check the Nutrition Facts label for added B12.

Supplements. B12 is in most multivitamins and prenatal vitamins, B-complex vitamins, and B12-only supplements. Research hasn’t shown that any one form is better than another, and high doses like 500 or 1,000 mcg are considered safe, though your body absorbs only a small share. B12 hasn’t been shown to cause harm, even at high doses. It also doesn’t boost energy in people who already get enough, despite the marketing.

Testing and treatment

Testing. A blood test can check your B12 level. Your provider may also check homocysteine, which builds up when B12, folate, or B6 is low, according to MedlinePlus, and a complete blood count to look for anemia.

Treatment depends on the cause, according to the NIH:

  • If your diet is the issue, B12 supplements or fortified foods usually fix it.
  • If you can’t absorb B12, as with pernicious anemia, doctors usually give B12 shots. A prescription nasal gel is also available, and very high doses by mouth may work for some people.
  • If a medicine like metformin or an acid reducer is the cause, your provider may recommend a supplement rather than stopping a medicine you need.

The folate connection

B12 and folate work together, which is why low levels of either one cause the same type of anemia, with large, poorly working red blood cells. That overlap creates two practical issues:

  1. Folic acid can hide B12 deficiency. Large amounts of folic acid can correct the anemia while B12-related nerve damage continues, according to the NIH. This is the main reason for the 1,000 mcg daily upper limit on folic acid.
  2. Low B12 can make folate test results look high. Without enough B12, cells can’t use folate, so it can build up in the blood. See our article on high folate levels.

If you’re being checked for anemia or taking high-dose folic acid, ask that B12 be checked too.

Related reading

Sources

This article is for general information and is not a substitute for advice from your health care provider.