Vitamin B12 – Function, Sources, Daily Requirements

Vitamin B12, also known scientifically as cobalamin, is a water-soluble vitamin that belongs to the B-complex group of vitamins. It is unique because it contains the mineral cobalt at its core, which gives it its characteristic name. Unlike many other vitamins, Vitamin B12 is not synthesized by plants or animals but is produced by certain bacteria and archaea. Animals obtain it through their diet or gut microbes, and humans, in turn, get it mainly from animal-derived foods.

This vitamin plays a fundamental role in many physiological processes. It is necessary for the formation of healthy red blood cells, synthesis of DNA, and proper functioning of the nervous system. One of its most critical functions is in the production of myelin, the protective covering around nerves that allows electrical impulses to transmit efficiently. Without adequate Vitamin B12, nerves become damaged, leading to neurological problems.

Absorption of Vitamin B12 in the human body is a complex process. It requires a protein known as the intrinsic factor, which is produced in the stomach. The vitamin binds to this protein and is then absorbed in the small intestine, mainly in the ileum. Any disruption in this mechanism, such as autoimmune conditions, gastrointestinal surgery, or chronic digestive disorders, can impair absorption and lead to deficiency even if dietary intake is sufficient.

Vitamin B12 exists in several forms, including methylcobalamin, adenosylcobalamin, hydroxocobalamin, and cyanocobalamin. Among these, methylcobalamin and adenosylcobalamin are the active forms that the body utilizes for metabolic functions. In supplements, cyanocobalamin is commonly used due to its stability, while hydroxocobalamin is often preferred in medical treatments, especially for injections.

Unlike some other vitamins, Vitamin B12 can be stored in the liver for several years, which is why deficiency may take time to develop. However, once stores are depleted, the effects can be severe, affecting both blood formation and neurological health.

Functions of Vitamin B12

One of the primary functions of Vitamin B12 is in the formation of red blood cells. It is involved in the production and maturation of these cells in the bone marrow. Without sufficient Vitamin B12, red blood cells develop abnormally, becoming larger and irregular in shape. This leads to a condition known as megaloblastic anemia, where the blood cannot carry oxygen efficiently, resulting in fatigue, weakness, and pale skin.

Another critical role of Vitamin B12 is in DNA synthesis. DNA, the genetic material present in every cell, needs Vitamin B12 to replicate correctly during cell division. A deficiency can disrupt this process, leading to improper cell growth and function. This is especially important for rapidly dividing cells, such as those in the bone marrow and the lining of the gastrointestinal tract.

Vitamin B12 also plays a central role in the nervous system. It is necessary for the production of myelin, the protective sheath that surrounds and insulates nerve fibers. Myelin ensures that signals travel quickly and efficiently between the brain, spinal cord, and the rest of the body. Without Vitamin B12, myelin is damaged, which can cause symptoms such as numbness, tingling, memory loss, mood changes, and even long-term neurological disorders.

In addition, Vitamin B12 is important for the metabolism of macronutrients. It works closely with folate (Vitamin B9) and Vitamin B6 to help in the metabolism of proteins and fats. It also assists in converting carbohydrates into glucose, which the body uses as a source of energy. This is why adequate Vitamin B12 levels are often linked with maintaining energy levels and reducing feelings of tiredness.

Another vital function of Vitamin B12 is in the regulation of homocysteine levels in the blood. Homocysteine is an amino acid that, when present in high amounts, is associated with an increased risk of heart disease and stroke. Vitamin B12, along with folate and Vitamin B6, helps break down homocysteine into methionine, thereby protecting cardiovascular health.

For pregnant women, Vitamin B12 is particularly important because it supports fetal growth and development. It ensures proper neural tube formation and prevents developmental problems in the baby.

Dietary Sources of Vitamin B12

Vitamin B12 is unique among vitamins because it is not naturally produced by plants or animals. Instead, it is synthesized by certain bacteria and microorganisms. Animals obtain it from their diet or gut microbes, and humans primarily receive it through the consumption of animal-derived foods. For this reason, Vitamin B12 is often referred to as a nutrient of concern for people who follow vegetarian or vegan diets.

The richest sources of Vitamin B12 are animal-based foods. Meat, poultry, and fish provide high amounts of this vitamin. For example, organ meats like liver and kidney are particularly concentrated in Vitamin B12. Fish such as salmon, tuna, trout, and sardines are also excellent sources, offering both Vitamin B12 and healthy omega-3 fatty acids. Poultry, including chicken and turkey, provides moderate levels, while red meats like beef and lamb are among the most reliable sources.

Dairy products are another important source. Milk, yogurt, and cheese contain Vitamin B12 in varying amounts, making them valuable options for vegetarians who consume dairy. Eggs, particularly the yolk, also supply a good quantity of this vitamin. These foods form the primary source of Vitamin B12 for lacto-ovo vegetarians.

For individuals who do not consume animal products, fortified foods are the most practical dietary option. Many plant-based products such as breakfast cereals, plant-based milk (soy, almond, oat), nutritional yeast, and meat substitutes are fortified with Vitamin B12. The fortification process ensures that vegetarians and vegans can still maintain adequate levels of the vitamin without relying on animal foods. Nutritional yeast, in particular, is popular because it not only provides B12 but also adds flavor to plant-based dishes.

In addition to natural and fortified sources, dietary supplements are widely available. These come in the form of tablets, capsules, or liquid drops and usually contain cyanocobalamin or methylcobalamin. Supplements are especially important for people with medical conditions that impair absorption, such as pernicious anemia, gastrointestinal surgeries, or chronic digestive disorders. In some cases, Vitamin B12 is also administered by injection under medical supervision to bypass absorption difficulties.

It is important to note that while some seaweeds and fermented foods are claimed to contain Vitamin B12, the forms present are often inactive analogues that the human body cannot use effectively. Relying on these sources may give a false sense of security and still result in deficiency.

Vitamin B12 is naturally abundant in animal-derived foods like meat, fish, dairy, and eggs, while fortified foods and supplements provide essential alternatives for vegetarians, vegans, and those with absorption issues.

Daily Requirements of Vitamin B12

The body needs only a small amount of Vitamin B12, yet this small quantity is vital for normal blood formation, DNA synthesis, and neurological function. Since the body cannot produce Vitamin B12 on its own, it must be obtained from diet or supplements. The requirement can vary depending on age, gender, and special physiological conditions such as pregnancy and breastfeeding.

The Recommended Dietary Allowance (RDA) for Vitamin B12 has been established by health authorities such as the National Institutes of Health (NIH) and the Indian Council of Medical Research (ICMR). These values indicate the daily intake necessary to maintain adequate levels and prevent deficiency.

For infants, the requirement is very small because their bodies are still developing. Babies aged 0–6 months need about 0.4 micrograms (mcg) per day, while those between 7–12 months require around 0.5 mcg daily. This is usually met through breast milk if the mother has sufficient Vitamin B12 levels or through fortified formula.

As children grow, their needs increase. Between the ages of 1–3 years, the recommended intake is about 0.9 mcg per day, rising to 1.2 mcg for children aged 4–8 years and 1.8 mcg for those aged 9–13 years. During adolescence, when rapid growth and development take place, the requirement increases to about 2.4 mcg per day.

For healthy adults, the general recommendation is 2.4 mcg per day. This amount is typically sufficient to maintain red blood cell production, neurological health, and overall metabolic balance.

The needs become higher during certain life stages. Pregnant women are advised to consume about 2.6 mcg daily, since Vitamin B12 is essential for proper fetal brain and nervous system development. During lactation, the requirement rises further to 2.8 mcg per day, as the vitamin is passed to the baby through breast milk. Meeting this demand ensures that the infant receives enough Vitamin B12 during the crucial early months of growth.

It is important to highlight that while the RDA sets the minimum daily intake, many individuals—especially older adults—may require higher amounts. With age, the ability to absorb Vitamin B12 decreases due to reduced stomach acid and lower production of intrinsic factor. For such individuals, fortified foods or supplements are often recommended, sometimes in doses much higher than the RDA to ensure sufficient absorption.

Deficiency of Vitamin B12

Vitamin B12 deficiency occurs when the body does not receive or properly absorb enough of this essential nutrient to meet its needs. Since Vitamin B12 plays a crucial role in red blood cell formation, DNA synthesis, and nervous system health, its deficiency can lead to a wide range of health problems that may progress from mild to severe if left uncorrected.

One of the major causes of deficiency is inadequate dietary intake. Since natural Vitamin B12 is found almost exclusively in animal products, individuals following a strict vegetarian or vegan diet are at higher risk. If their diet does not include fortified foods or supplements, deficiency can develop gradually.

Another significant factor is impaired absorption. For Vitamin B12 to be absorbed, it must bind with a special protein called intrinsic factor, produced in the stomach. In people with pernicious anemia, an autoimmune condition, the body cannot produce intrinsic factor, leading to poor absorption of Vitamin B12 even if dietary intake is adequate. Similarly, individuals who have undergone gastrointestinal surgeries such as gastric bypass, or those with chronic conditions like Crohn’s disease, celiac disease, or atrophic gastritis, often face difficulties in absorbing the vitamin.

Age-related changes also contribute to deficiency. Older adults frequently develop low stomach acid levels, which reduces their ability to release Vitamin B12 from food proteins during digestion. This makes them more susceptible to deficiency compared to younger adults.

Certain medications can interfere with Vitamin B12 absorption as well. Long-term use of drugs like proton pump inhibitors (used for acidity), H2 receptor blockers, and metformin (commonly prescribed for diabetes) is associated with reduced Vitamin B12 levels.

In infants and children, deficiency may occur if the mother herself is deficient during pregnancy or breastfeeding, as the child’s supply depends on maternal intake. This can lead to developmental delays and neurological problems if not addressed promptly.

The effects of Vitamin B12 deficiency are broad. It commonly causes megaloblastic anemia, characterized by abnormally large and poorly formed red blood cells. Beyond anemia, the deficiency also leads to neurological complications, since Vitamin B12 is required for maintaining healthy nerves and producing neurotransmitters. If untreated for a long time, these neurological effects may become permanent.