Vitamin B12 is an essential nutrient that your body needs for processes, like DNA synthesis, energy production, and central nervous system function.

Even though the vitamin is found in many foods, B12 insufficiency and deficiency are relatively common. This is often due to limited dietary intake, malabsorption, certain medical conditions, or the use of B12-depleting medications. In fact, studies suggest that up to 20% of people over the age of 60 are deficient in the vitamin.

the ability to absorb B12 from food declines with age, deficiency is more common in older adults. Still, that doesn’t mean children and younger adults, including those who are pregnant and breastfeeding, can’t develop B12 deficiency.

Unfortunately, B12 deficiency is often overlooked and misdiagnosed. Oftentimes, this is due to inadequate laboratory testing or because the symptoms are not specific to vitamin B12 deficiency alone. If you suspect you might have a B12 deficiency, it’s important to visit a healthcare professional to discuss your symptoms and undergo appropriate testing.

Vitamin B12, or cobalamin, is naturally found in animal foods. It can also be added to foods or supplements. Vitamin B12 is needed to form red blood cells and DNA. It is also a key player in the function and development of brain and nerve cells.

Vitamin B12 binds to the protein in the foods we eat. In the stomach, hydrochloric acid and enzymes unbind vitamin B12 into its free form. From there, vitamin B12 combines with a protein called intrinsic factor so that it can be absorbed further down in the small intestine.

Supplements and fortified foods contain B12 in its free form, so they may be more easily absorbed. There is a variety of vitamin B12 supplements available. Although there are claims that certain forms—like sublingual tablets or liquids placed under the tongue to be absorbed through the tissues of the mouth—have better absorption than traditional tablets, studies have not shown an important difference. Vitamin B12 tablets are available in high dosages far above the recommended dietary allowance, but these high amounts are not necessarily the amount that will be absorbed because an adequate amount of intrinsic factor is also needed. In cases of severe vitamin B12 deficiency due to inadequate intrinsic factor (pernicious anemia), doctors may prescribe B12 injections in the muscle.

Signs of Deficiency and Toxicity

Deficiency 
Measuring vitamin B12 in the blood is actually not the best way to determine whether someone is deficient, as some people with a deficiency can show normal B12 blood levels. Blood levels of methylmalonic acid, a protein breakdown product, and homocysteine are better markers that capture actual vitamin B12 activity. These values increase with a vitamin B12 deficiency. It is estimated that up to 15% of the general population has a vitamin B12 deficiency.

Factors that may cause vitamin B12 deficiency:

• Avoiding animal products. People who do not eat meat, fish, poultry, or dairy are at risk of becoming deficient in vitamin B12, since it is only found naturally in animal products. Studies have shown that vegetarians have low vitamin B blood levels. For this reason, those who follow a vegetarian or vegan diet should include B12-fortified foods or a B12 supplement in their diets. This is particularly important for pregnant women, as the fetus requires adequate vitamin B12 for neurologic development and deficiency can lead to permanent neurological damage.

• Lack of intrinsic factor. Pernicious anemia is an autoimmune disease that attacks and potentially destroys gut cells so that intrinsic factor is not present, which is crucial for vitamin B12 to be absorbed. If vitamin B12 deficiency ensues, other types of anemia and neurological damage may result. Even the use of a high-dose B12 supplement will not solve the problem, as intrinsic factor is not available to absorb it.
• Inadequate stomach acid or medications that cause decreased stomach acid. A much more common cause of B12 deficiency, especially in older people, is a lack of stomach acid, because stomach acid is needed to liberate vitamin B12 from food. An estimated 10-30% of adults over the age of 50 have difficulty absorbing vitamin B12 from food. People who regularly take medications that suppress stomach acid for conditions like gastroesophageal reflux disease (GERD) or peptic ulcer disease—such as proton-pump inhibitors, H2 blockers, or other antacids—may have difficulty absorbing vitamin B12 from food. These drugs can slow the release or decrease production of stomach acid. In theory this can prevent the vitamin from being released into its free usable form in the stomach; however, research has not shown an increased prevalence of a deficiency in people using these medications. Anyone using these medications for an extended time and who are at risk for a vitamin B12 deficiency for other reasons should be monitored closely by their physician. They may also choose to use fortified foods or supplements with vitamin B12, as these forms are typically absorbed well, and do not require stomach acid.
• Intestinal surgeries or digestive disorders that cause malabsorption. Surgeries that affect the stomach where intrinsic factor is made, or the ileum (the last portion of the small intestine) where vitamin B12 is absorbed, can increase the risk of a deficiency. Certain diseases including Crohn’s and celiac disease that negatively impact the digestive tract also increase the risk of deficiency.

Signs of deficiency may include:

• Megaloblastic anemia—a condition of larger than normal sized red blood cells and a smaller than normal amount; this occurs because there is not enough vitamin B12 in the diet or poor absorption
• Pernicious anemia—a type of megaloblastic anemia caused by a lack of intrinsic factor so that vitamin B12 is not absorbed
• Fatigue – If you’re low or deficient in B12, you’ll likely feel fatigued. Your body’s cells need B12 to function properly. As such, having inadequate B12 levels can decrease normal red blood cell production, which can impair oxygen delivery. Specifically, a deficiency in B12 or folate can cause megaloblastic anemia. This condition leads to the formation of large, abnormal, and immature red blood cells and impaired DNA synthesis. when your body doesn’t have enough healthy red blood cells to carry oxygen to tissues, you’ll likely feel weak and tired. It’s important to know that you can develop fatigue and other symptoms related to B12 deficiency, even when your B12 levels are considered within range or only borderline low

• Nerve damage with numbness, tingling in the hands and legs
• Memory loss, confusion
• Dementia
• Depression- B12 is essential to the proper functioning of your central nervous system, and a deficiency in this nutrient can impact your mental health. Specifically, B12 deficiency is associated with a greater risk of developing depression, having low levels of B12 can cause elevated levels of a sulfur-containing amino acid called homocysteine. In turn, this may contribute to the development of depression by increasing oxidative stress, DNA damage, and cell death in the body. A 2020 study with 132 children and teens, 89 with and 43 without depression, found that the participants with depression had lower B12 levels and higher levels of homocysteine compared with those without depression. In addition to depressive symptoms, low or deficient B12 levels may lead to other mental conditions, including psychosis and mood disorders.
• Seizures

Toxicity 
Vitamin B12 is a water-soluble vitamin, so any unused amount will exit the body through the urine. Generally, up to 1000 mcg a day of an oral tablet to treat a deficiency is considered safe. The Institute of Medicine states “no adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals.” However, it is important not to start a high-dosage supplement of any kind without first checking with your doctor.

Did You Know? 

• A B vitamin complex supplement is often touted to boost energy levels and mood. People who have a B vitamin deficiency may feel a rise in energy levels after using the supplement because the vitamin is directly involved in making healthy blood cells and can correct anemia if present. However, there is no evidence of benefit if people without a deficiency take extra B vitamins.

• People who eat a vegan diet are often told to include Brewer’s or nutritional yeast for its B12 content. However, yeast does not naturally contain this vitamin and will only be present if fortified with it. Be aware that certain brands, but not all, contain B12.
• Nori (purple laver), the dried edible seaweed used to make sushi rolls, is sometimes promoted as a plant source of vitamin B12. It does contain small amounts of active vitamin B12, but the amount varies among types of seaweed, with some containing none. Therefore, is not considered a reliable food source.

Treatment can help you get better. If you have a serious deficiency, your doctor will probably give you B12 through a shot in your muscle or a daily high-dose supplement. You may need to make changes to your diet, too. Boost your B12 levels with these foods.

1. Fish and Shellfish
This is how much B12 you’ll find in a 3-ounce serving of these foods:

• Cooked clams: 84.1 micrograms
• Steamed mussels: 20.4 micrograms
• Cooked Atlantic mackerel: 16.1 micrograms
• Steamed Alaska king crab: 9.8 micrograms
• Cooked wild rainbow trout 5.4 micrograms
• Cooked salmon: 2.4 micrograms

2. Red Meat
This includes beef and lamb. Like humans, large amounts of B12 are stored in their livers.

Here’s what you can get from 3-ounce servings of the following:

• Cooked beef liver: 70.7 micrograms
• Grilled lean beef, steak: 6.9 micrograms

Too much red meat can raise your chances for certain health conditions. That includes heart and blood vessel problems and certain kinds of cancer. You may want to limit it to a few servings a week. Ask your doctor how much is safe for you.

3. Dairy
Cows also pass B12 into their milk. This is what you’ll find in the following:

• Low-fat milk, 1 cup: 1.2 micrograms
• Low-fat yogurt, 8 ounces: 1.2 micrograms
• Swiss cheese, 1 ounce: 0.9 micrograms

4. Poultry
You can find some B12 in chicken and turkey.

• Cooked turkey liver, 3 ounces: 23.9 micrograms
• Cooked chicken liver, 1 ounce: 4.7 micrograms
• Cooked ground lean turkey, 3 ounces: 1.6 micrograms
• Roasted turkey, 3 ounces: 0.8 micrograms
• Roasted chicken breast, 3 ounces: 0.3 micrograms

5. Eggs
One hard-boiled egg has about 0.6 micrograms of B12. That’s 25% of your daily value. But you’ll need to eat the whole egg. Most of the B12 comes from the yolk.

If you have a deficiency, eggs shouldn’t be your main source of B12. There’s not a lot of evidence that they can raise your levels of B12 all that much. 

6. Vegan or Vegetarian Sources
It’s harder to get your B12 from food if you’re on a strict plant-based diet. That means you don’t eat any animal products, including eggs or dairy. Your doctor will likely suggest taking a daily or weekly dietary supplement to keep your levels up. They can let you know what dose is right for you.

You can get B12 from some plant-based sources. These include fortified foods with added nutrients.

• Fortified non-dairy milks, such as soy or oat, 1 cup: 0.6-2.07 micrograms
• Fortified cereals, one serving: 0.6-2.1 micrograms
• Nutritional yeast, 1 tablespoon: 4.8 micrograms

Always read the nutrition label to see how much B12 you’re getting per serving.

Some fermented foods and seaweed have B12. It comes from their exposure to bacteria. You shouldn’t depend on them for all your B12 needs. But you can still add them to your diet. They include:

Tempeh. This is a fermented soybean cake. Studies show that one serving may have anywhere from 0.7-8.0 micrograms. But it’s hard to know exactly how much you’ll get in the kind you find at the grocery store.

Nori. These are dried sheets of seaweed. You’ve probably seen them used to make sushi. Studies show it might be possible to get 2.4 micrograms of B12 from 4 grams of nori. But you’d need to eat a little more than 13 sheets to meet your daily intake. 

If you’ve been vegan or a strict vegetarian for more than a few years, ask your doctor to check your B12. A simple blood test can show if your levels are where they should be.

When Food Isn’t Enough?
Treatment for your B12 deficiency depends on what’s causing it. Older age and certain health conditions, like pernicious anemia, can make it hard for your stomach to absorb B12 from food. Your doctor can run some tests to find out if you have these problems. You may need regular B12 shots or dietary supplements to stay healthy. 

B12 deficiency can cause a variety of symptoms, including fatigue, headaches, depression, pale or yellow skin, mental impairment, and pain and inflammation in the mouth and tongue. Many of the symptoms caused by low B12 levels are not specific to B12 deficiency, which can cause the condition to go undetected. If you’re experiencing any of the symptoms listed above, it’s important to visit a healthcare professional to undergo appropriate testing and get the right treatment.