Vitamin B12

Studies in people

• Open question

  Long-term health effects³

  Low vitamin B12 may affect pregnancy, blood vessels, memory, bones and eyes, but the long-term effects are not fully known.

• Open question

  Low energy and tingling⁴

  Low vitamin B12 can cause tiredness, brain fog and tingling, and is treated with vitamin B12 pills or shots.

• Open question

  Pregnancy health⁵

  Vitamin B12 supplements in pregnancy may raise vitamin B12 levels, but scientists do not yet know whether they improve other health outcomes.

• Concern

  Folic acid risks⁷

  In people, high-dose folic acid may worsen vitamin B12 deficiency, but scientists do not yet know for sure.

• Benefit

  Nerve damage in diabetes⁹

  In people with diabetic nerve damage, taking vitamin B12 pills for a year eased pain and improved feeling in their feet.

• Benefit

  Oral treatment for anemia¹⁰

  In people with pernicious anemia, taking vitamin B12 by mouth corrected the deficiency in most within a month.

• Open question

  Spotting a hidden shortage¹²

  Vitamin B12 shortage is common in older people, and doctors have no single agreed test to spot it.

• Open question

  Poor absorption of nutrients¹⁴

  Vitamin B12 shortage is most often caused by eating too few animal foods or by the gut not absorbing it.

• Open question

  Sources and deficiency causes¹⁵

  Vitamin B12 comes from animal foods like eggs, milk, meat and fish, and low levels can come from diet or poor absorption.

• Open question

  B12 and autism symptoms¹⁸

  Scientists do not yet know whether vitamin B12 levels affect autism symptoms, since studies so far disagree.

• Benefit

  Teenage bone strength²⁰

  Teens who ate more vitamin B12 tended to have denser bones, but scientists say more studies are needed to confirm this.

• Open question

  Diet and nutrient gaps²¹

  In a Slovenian study, 58.3% of elderly people got too little vitamin B12 from food.

• Open question

  Brain development in young children²⁴

  Over a third of Indian infants and toddlers tested low in vitamin B12, which matters for growing brains.

Animal and lab studies only

• Open question

  Stroke recovery³⁰

  In animal studies, mice lacking vitamin B12 had worse movement after a stroke than mice with enough.

How it’s made and used

• B12 absorption problems²

  Vitamin B12 needs help from the body to be absorbed, and many gut problems can block this.

• How much the body absorbs⁶

  How much vitamin B12 the body absorbs drops as the amount eaten in one meal goes up.

• Blood and nerve health⁸

  Vitamin B12 deficiency can affect the blood, bone marrow and nervous system, causing anemia and nerve problems.

• Injection causing acne¹¹

  In one study, one of ten people given vitamin B12 injections got acne a week later.

• Breastfed babies vitamin deficiency¹³

  Babies fed only breast milk got vitamin B12 deficiency from their mothers, but treatment restored them to health.

• Plant diet nutrient gap¹⁶

  Vegetarians may not get enough vitamin B12 from plants alone, so a supplement is often needed.

• B12 deficiency risk¹⁷

  Vegan adults had lower vitamin B12 levels than meat eaters, but vitamin B12 supplements improved their levels.

• Vitamin levels in children¹⁹

  Children and teens on vegan or macrobiotic diets had lower vitamin B12 levels than those eating meat.

• Blood pressure risk²²

  In 1,398 adults in rural India, low vitamin B12 went with higher homocysteine, which was linked to high blood pressure.

• B12 and body weight²³

  Obese pregnant women had lower vitamin B12 levels than women with a normal BMI.

• Infant development and blood health²⁵

  Babies with low vitamin B12 showed delayed development, poor growth, and anemia, but improved after treatment.

• Supplement use among vegans²⁶

  Most Austrian vegans in this survey took vitamin B12 through supplements or fortified foods.

• B vitamin intake effects²⁷

  In older people, a doubling of vitamin B12 intake was linked to higher blood levels of the vitamin.

• Birth defects in babies²⁸

  Low vitamin B12 in pregnancy is linked to a higher risk of neural tube defects.

• Brain health and memory²⁹

  Vitamin B12 may play a role in Alzheimer's disease, and vegetarian or vegan diets can lead to low B12.

The signal at the top counts the findings in people and in animal and lab studies. A concern in studies of people outranks animal and lab studies, and “No concerns” needs at least one finding in people. When most findings in people point one way, the page leans that way (“Mostly”), and every finding is still shown. Findings whose study type is not stated are shown but not counted. This page is a reference, not medical advice. It describes what regulators and published research say. Talk to a doctor or dietitian about your own diet.