What Is Vitamin B12

What Is Vitamin B12

Vitamin B12, also called cobalamin, is a water-soluble vitamin that plays a vital role in keeping your body’s nerve and blood cells healthy and in making DNA—the genetic material in all cells. It’s one of the eight B-vitamins, but it stands out because of its complexity and unique role in neurological and red blood cell function.

Unlike most vitamins, B12 contains cobalt, a trace mineral, and is found naturally only in animal-based foods or those fortified with it. That’s why vegetarians and vegans often need supplements or fortified foods to maintain adequate levels.

Functions of Vitamin B12

Formation of Red Blood Cells

Vitamin B12 helps the bone marrow produce healthy red blood cells. Without it, red blood cells become large, irregularly shaped, and unable to carry oxygen efficiently. This condition is known as megaloblastic anaemia. Symptoms include fatigue, weakness, pale skin, and shortness of breath.

Nervous System Health

B12 is essential for maintaining the myelin sheath, a protective covering around nerves that helps transmit electrical signals efficiently. A deficiency can cause nerve damage, tingling in the hands and feet, balance problems, and cognitive issues such as memory loss or confusion.

DNA Synthesis and Cell Division

Every cell in your body needs B12 to replicate properly. During growth, repair, or tissue maintenance, B12 works with folate (vitamin B9) to ensure accurate DNA replication. Deficiency can impair this process and slow tissue recovery.

Energy Production

Though B12 doesn’t directly provide energy like carbohydrates or fats, it’s crucial in metabolic pathways that convert food into energy. A lack of B12 can therefore lead to feelings of tiredness and sluggishness.

Mental Health and Brain Function

B12 helps synthesise neurotransmitters like serotonin and dopamine, which regulate mood. Low levels are linked to depression, anxiety, and cognitive decline, especially in older adults.

Daily Requirements

The Recommended Dietary Allowance (RDA) for adults is 2.4 micrograms (µg) per day.

Pregnant women need about 2.6 µg/day,

and lactating women need 2.8 µg/day.

Since the body stores B12 in the liver, deficiencies may take years to show up, but once depleted, recovery can be slow.

Sources of Vitamin B12

B12 is naturally found in animal products, since bacteria in animals’ digestive systems produce it.

Meat: beef, lamb, pork, and liver

Fish and seafood: salmon, tuna, trout, clams, sardines

Poultry: chicken, turkey, and eggs

Dairy: milk, cheese, yogurt

For vegetarians and vegans

Fortified foods such as plant-based milks, breakfast cereals, and nutritional yeast are reliable options.

Supplements (cyanocobalamin or methylcobalamin forms) are often necessary, especially for those on long-term plant-based diets.

Absorption and Metabolism

B12 absorption is a complex, multi-step process.

In the stomach, hydrochloric acid separates B12 from food proteins.

The vitamin then binds to a protein called intrinsic factor, secreted by stomach cells.

This B12-intrinsic factor complex travels to the small intestine, where it’s absorbed into the bloodstream.

People with digestive issues such as atrophic gastritis, celiac disease, or Crohn’s disease—or those who have had part of their stomach or intestines surgically removed—may have trouble absorbing B12 naturally.

Older adults often have lower stomach acid levels, which also reduces absorption, making supplementation important after age 50.

Deficiency: Symptoms and Risks

Vitamin B12 deficiency can cause a wide range of symptoms, from mild fatigue to serious neurological problems.

Tiredness, dizziness, and pale skin

Tingling or numbness in the hands and feet

Poor balance or coordination

Memory problems or confusion

Mood changes or depression

Swollen tongue or mouth ulcers

If untreated, the damage can become permanent, especially in the nervous system.

Groups at highest risk include

Vegans and vegetarians

Older adults

People with gastrointestinal disorders

Individuals on certain medications, such as metformin or proton pump inhibitors

Diagnosis and Treatment

A blood test can measure B12 levels directly. Levels below 200 pg/mL generally indicate deficiency, while 200–400 pg/mL may warrant further testing.

Treatment depends on severity

Mild cases respond to oral supplements or fortified foods.

Severe cases may need B12 injections (hydroxocobalamin or cyanocobalamin), which bypass the digestive tract entirely.

Toxicity and Safety

Vitamin B12 is very safe, even at high doses, because excess amounts are excreted in urine. No upper intake limit has been established. However, unnecessary megadoses should be avoided unless prescribed for medical reasons.

Summary

Vitamin B12 is a powerhouse nutrient vital for red blood cell formation, nerve function, DNA synthesis, and energy metabolism. Because it’s mainly found in animal foods, plant-based eaters and older adults must pay close attention to their intake. Maintaining adequate B12 levels supports a healthy brain, energetic body, and long-term vitality.

In short: a few micrograms a day make a huge difference to how clearly you think, how well you move, and how alive you feel.