Written by Anne Jacobson, MD, MPH | Reviewed by Sophie Vergnaud, MDPublished on March 11, 2022 print_outlinedemail_outlined
Key takeaways:
- Vitamin B12 is needed for healthy blood cells, nerve cells, and DNA.
- Vitamin B12 is found naturally in meat, eggs, and dairy and may be added to other foods.
- You can be deficient in vitamin B12 if you don’t get enough in your diet or your gut can’t absorb it.
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Vitamin B12 is a nutrient that does its job quietly and efficiently inside our cells. We need vitamin B12 to make new DNA and keep nerve cells and blood cells healthy. It also helps our cells break down proteins and fats for energy.
Most of us get enough vitamin B12 in our diet and absorb it through the digestive system. But some diets and certain health conditions, especially as we age, may lead to a deficiency of this important vitamin.
What is vitamin B12?
Vitamin B12, also called cobalamin, is one of the B-complex vitamins. It’s not made by the body, so we need it in our diet. Vitamin B12 is not made by plants, either. It’s found in animal products, in foods where B12 has been added, or in supplement form.
Teens and adults need about 2.4 micrograms of Vitamin B12 every day. Pregnant people need around 2.6 micrograms, and those who are breastfeeding need 2.8. Infants and children need 0.4 to 1.8 micrograms, depending on their age.
Vitamin B12 is more easily used by the body in certain forms. For example, it’s in meat, poultry, fish, and eggs but is most easily used by the body in dairy products. And vitamin B12 is more readily available for the body in supplement form than it is in foods. Vitamin B12 is also present in breast milk and added to infant formula. Extra B12 is stored in the liver, in case our cells need to use it in the future.
Symptoms of B12 deficiency
Not having enough B12 can affect how well the body makes new blood cells, nerve cells, and DNA.
Anemia
Low B12 levels cause a kind of anemia, or low blood count. Sometimes the blood cells become large, or macrocytic, before a person becomes anemic.
Symptoms of anemia might include:
- Feeling tired or having low energy
- Pale skin
- Feeling short of breath, especially with movement
- Having less of an appetite or losing weight without trying
- Headaches
- Feeling dizzy or like you might faint
- Fast or irregular heartbeat
Some people with B12 deficiency also have mouth sores or a swollen, painful tongue.
Nerve damage
Vitamin B12 is also important for nerve cells to function. B12 deficiency can affect the central nervous system (the brain and spinal cord) or peripheral nerves that go to the rest of the body.
Symptoms of nerve damage from B12 deficiency can include:
- Tingling, or a pins-and-needles sensation
- Depression, irritability, or confusion
- Changes in vision
- Memory loss
- Problems with balance
If a pregnant person doesn’t have enough B12 and folate, a baby may be born with a neural tube defect. This happens when the brain or spinal cord develop incorrectly. Because vitamin B12 is also present in breast milk, a breastfed baby whose parent has a low B12 level could have delayed development, slow weight gain, or anemia.
Vitamin B12 and DNA
Our cells need vitamin B12 to make new DNA. When cells can’t make or repair DNA, they start to divide incorrectly. Low B12 and folate levels play a role in DNA damage, which may lead to diseases like cancer. This is also why low vitamin B12 is thought to affect heart disease, stroke, and dementia.
What causes B12 deficiency?
The body stores extra vitamin B12 in the liver. So, it may take years for someone to develop symptoms from a B12 deficiency. But there are certain conditions that put some people more at risk.
Not consuming enough
Vitamin B12 comes from animal products like eggs, dairy products, poultry, fish, and meat. It’s also added to some foods like cereals and nutritional yeast. Most people in the U.S. consume enough vitamin B12.
But you could be at risk for B12 deficiency if you follow a strict vegan or vegetarian diet and don’t take a supplement or eat other foods that are fortified with vitamin B12. The infants of pregnant or breastfeeding people who don’t get enough vitamin B12 are also at risk.
The amount of vitamin B12 can be found on the nutrition label of foods where it has been added and doesn’t occur naturally.
Not absorbing enough
Some people consume enough vitamin B12 but their body can’t absorb it. Some health conditions that may affect B12 absorption include:
- Weight-loss surgery or other surgery on the stomach and intestines
- Low stomach acid, occurring with age or from taking medications to reduce stomach acid.
- Inflammation in the stomach or small intestine from gastritis, celiac disease, or Crohn’s disease
- Pernicious anemia, an autoimmune condition where the stomach doesn’t make a protein that is needed to absorb B12
- Taking metformin for diabetes may decrease B12 absorption
- Drinking alcohol can interfere with the body’s ability to absorb enough B12
How is B12 deficiency diagnosed?
A healthcare provider may test your B12 blood level if you have a risk factor for deficiency. A physical exam can provide clues, but you may not have any symptoms or obvious changes on an exam.
A blood test will look for anemia and the size of the blood cells. B12 levels can also be checked in the blood. More specialized tests may be done for advanced disease or if autoimmune disease is suspected.
Treating B12 deficiency
Depending on the severity and cause, there are oral, nasal, or injected forms of B12 treatment. If the B12 deficiency isn’t severe and was caused by not consuming enough, it can often be treated with a supplement that is taken by mouth.
Severe B12 deficiency — especially if it’s caused by an absorption problem or autoimmune condition — is usually treated with B12 injections. This may be for a period of time, or it may be for life, depending on the condition. There is also a
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