Cobalamine (B12)

What is vitamin B12?

Vitamin B12, also known as cobalamin, is an essential nutrient that supports red blood cell formation, brain health, and DNA production. Vitamin B12 is a water-soluble vitamin, meaning it dissolves in water and can be easily cleared from the body. There are different forms of vitamin B12, including methylcobalamin and 5-deoxyadenosylcobalamin (the active forms), as well as hydroxycobalamin and cyanocobalamin (which can be converted to the active forms in the body).¹ Since our bodies cannot produce vitamin B12, we must get this nutrient through our diet.

Why we need it

Vitamin B12 serves as a coenzyme (a substance required by an enzyme for a reaction to take place) for two enzymes. The first is methionine synthase, which catalyzes the formation of the essential amino acid methionine.¹ The next is L-methylmalonyl-CoA mutase, which catalyzes the formation of succinyl-CoA, a compound that helps us generate energy from the food we eat.¹

Through its coenzyme activity, vitamin B12 supports many important bodily processes. It is required for the formation of red blood cells, which transport oxygen throughout the body.² Vitamin B12 is also involved in the production of myelin, a protective substance that coats our brain cells and allows signals to be transmitted more effectively throughout the brain.³ Furthermore, vitamin B12 helps us produce DNA, the substance that carries our genetic information.² Vitamin B12 also participates in energy production and fatty acid synthesis, among other processes.³

Where it’s found

Vitamin B12 is naturally found only in animal-based foods. However, it may be added into various plant-based foods through a process called fortification. Examples of vitamin B12-rich foods include:

Meat
Poultry
Fish and seafood
Eggs
Milk and dairy products
Fortified breakfast cereals
Nutritional yeast

Vitamin B12 can also be taken as a supplement, either by itself or as part of a multivitamin or B-complex supplement. Vitamin B12 supplements are available in many forms, including capsules, tablets, lozenges, and even nasal sprays.⁴

Daily requirements

The daily Recommended Dietary Allowance (RDA) for vitamin B12 (i.e. the amount that is likely to meet the needs of most healthy people) is 0.9 micrograms (µg) for children aged 1-3 years, 1.2 µg for children aged 4-8 years, 1.8 µg for children aged 9-13 years, and 2.4 µg for individuals aged 14 and up.¹ For women who are pregnant or breastfeeding, the RDA increases to 2.6 µg and 2.8 µg, respectively.¹

Vitamin B12 deficiency

Vitamin B12 deficiency can have many negative effects, mainly on the blood and the nervous system. It can cause megaloblastic anemia, a condition characterized by abnormally large red blood cells. Symptoms of megaloblastic anemia include pale skin, fatigue, and shortness of breath.¹ Vitamin B12 deficiency can also cause neurological issues such as difficulty balancing, changes in visual function, memory loss, mood changes, and tingling in the hands and feet.¹

Clinical vitamin B12 deficiency (i.e., diagnosed deficiency with the classic signs and symptoms) is relatively rare.⁵ However, subclinical deficiency (i.e., being below the optimal level but not to the point of outright deficiency) is fairly common, especially among older adults.⁵

Vitamin B12 deficiency has several potential causes, including a diet low in vitamin B12. Given that vitamin B12 is mostly found in animal products, vegetarians and vegans are at higher risk for vitamin B12 deficiency. Another common cause of vitamin B12 deficiency is insufficient absorption of vitamin B12. This may be due to a lack of intrinsic factor, a substance that binds to vitamin B12 in the intestine and allows it to be absorbed. Thus, people with pernicious anemia (an autoimmune condition that blocks the production of intrinsic factor) face an increased risk for vitamin B12 deficiency.¹

Can you get too much vitamin B12?

There have been no reported adverse effects of vitamin B12 consumption, even at high doses.¹ For this reason, there is no Tolerable Upper Intake Level (i.e., a maximum amount of a nutrient that is considered to be safe) established for vitamin B12.¹

Fun facts

Vitamin B12 differs from other water-soluble vitamins in that it can be stored in the body in relatively large amounts. Because of this, it can take several years for symptoms of vitamin B12 deficiency to become noticeable.⁶

There are certain drugs that may interfere with vitamin B12 metabolism and increase the risk of deficiency. For example, nitrous oxide (or “laughing gas”) may inactive vitamin B12. For this reason, excessive nitrous oxide use may cause spinal cord damage, difficulty walking, and tingling in the hands and feet, due to an inability to produce myelin (as a consequence of vitamin B12 deficiency).⁷