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VITAMIN B12 (COBALAMIN)

Vitamin B12 is cobalamin. In the mid-19th century, many people suffered from pernicious anemia characterized by the appearance of enlarged and irregularly shaped red blood cells in the bloodstream. This was considered a fatal disease until the 1920s. In 1926, George Minot and William Murphy discovered that beef liver was effective in treating patients with pernicious anemia. Together with George Whipple, they shared the 1934 Nobel Prize in Physiology or Medicine for their contribution. In subsequent years, a water-soluble substance isolated from beef liver was called the “extrinsic factor,” and a protein produced in the stomach was called the “intrinsic factor.” In 1948, scientists confirmed that the chemical structure of the extrinsic factor was cobalamin and named it vitamin B12. The intrinsic factor was required for the absorption of vitamin B12 in the intestines.

Among all vitamins, vitamin B12 has the largest molecular weight and contains cobalt. Vitamin B12 participates in the metabolism of almost all cells in the body. It is an essential cofactor for the enzymatic conversion of homocysteine to methionine. Vitamin B12 deficiency can lead to high blood levels of homocysteine, increasing the risk of cardiovascular diseases. Vitamin B12 is also a cofactor for the enzymatic conversion of lipids and proteins to cellular energy and in the synthesis of new red blood cells.

What Are the Symptoms of Vitamin B12 Deficiency?

Vitamin B12 deficiency can lead to anemia, damage the nervous system, and, in men, lower sperm count. The major symptoms are fatigue, stabbing pain and numbness of the extremities, gait disturbance, and even the inability to walk. According to data from the Centers for Disease Control and Prevention, 2% of the US population and 4% of elderly people in the US are vitamin B12 deficient.

What Are the Causes of Vitamin B12 Deficiency?

 • Malabsorption. Malabsorption is the major cause of vitamin B12 deficiency. The absorption of vitamin B12 in the intestines is unique. First, stomach acid is required to dissolve and release vitamin B12 from foods. The “free” vitamin B12 then binds the intrinsic factor in the stomach to form a complex that is absorbed by the intestines. Insufficient stomach acid or intrinsic factor could hinder the absorption of vitamin B12 in the intestines, resulting in vitamin B12 deficiency.

 • Atrophic gastritis. About 10–30% of people aged 60 and older are afflicted by atrophic gastritis. Atrophic gastritis is caused by autoimmune disorders, resulting in immune cells wrongly attacking stomach cells. Atrophic gastritis lowers vitamin B12 absorption, leading to vitamin B12 deficiency. Furthermore, individuals age 60 and older have less stomach acid. Insufficient stomach acid affects the release of vitamin B12 from ingested foods, reduces the absorption of vitamin B12 in the intestines, and increases the risk of vitamin B12 deficiency.

Which Diseases Are Associated with Vitamin B12 Deficiency?

 • Pernicious anemia. Vitamin B12 is an essential nutrient for the synthesis of new red blood cells in bone marrow. Vitamin B12 deficiency can cause pernicious anemia, a condition that cannot be reversed by iron supplementation. Anemia often is the earliest sign of vitamin B12 deficiency. Pernicious anemia may be due to vitamin B12 deficiency or lack of intrinsic factor, which is required for vitamin B12 absorption in the intestines. Deficiency of either vitamin B12 or intrinsic factor can lead to pernicious anemia.

 • Nervous system disorders. Vitamin B12 deficiency triggers numbness in the extremities, memory loss, unconsciousness, and difficulty walking, and in severe cases, it can permanently damage the nervous system. People who take more than 400 mcg of a vitamin B9 supplement a day should be concerned about the potentially hidden problem of vitamin B12 deficiency. Vitamin B9 may cure anemia, but not the underlining problem of vitamin B12 deficiency. Vitamin B12 deficiency often goes unnoticed until the nervous system is permanently damaged.

 • Digestive system retardation. Stomach surgery or digestive system disorder can cause vitamin B12 deficiency. Lack of appetite and constipation are early signs of vitamin B12 deficiency.

Prevention and Treatment of Diseases

 • Prevention. Meta-analysis confirms that vitamin B12 can help prevent colorectal cancer (56), renal cell cancer (100), cervical cancer (50), multiple sclerosis (89), depression (58), and venous thrombosis (110).

 • Treatment. Meta-analysis reveals that vitamin B12 can help treat and prevent recurrent stroke (108).

Which Food Items Are Vitamin B12 Rich?

The human body cannot produce or store vitamin B12; therefore, it needs to be obtained from foods. Vitamin B12 mainly comes from animal-based foods. Plant-based foods such as mushrooms and miso also contain vitamin B12.

This list of vitamin B12–rich food items is adapted from information provided by the NIH Office of Dietary Supplements.

Daily reference value of vitamin B12 is 6 mcg according to the 2013 FDA food-labeling guidelines.

What Are the Recommended Dietary Allowances for Vitamin B12?

There is currently no upper intake limit for vitamin B12.

Vitamin B12 Supplements

 • Dosage. The most common dosages of vitamin B12 supplements are 500–1,000 mcg.

 • Types. Two major types of vitamin B12 supplements are cyanocobalamin and methylcobalamin. The former is synthetic and the latter naturally produced. In the intestines, cyanocobalamin is converted to methylcobalamin in a two-step process. First, cyanide is removed from cyanocobalamin to produce cobalamin, and then cobalamin is methylated to produce methylcobalamin. In the process, cyanide is released from cyanocobalamin, and though it’s only a small amount, cyanide is a toxin. So methylcobalamin is safer than cyanocobalamin, even though the former is more expensive than the latter.

 • Vegetarians. Vitamin B12 comes predominantly from animal-based foods, not from plant-based ones. Vegetarians should consider taking vitamin B12 supplementation at a dosage of 100 mcg daily or 700 mcg weekly.

 • Elderly. Supplementation with vitamin B12 is recommended for individuals aged 60 and older, particularly for those who take antacid medications.

 • Cognitive decline. Vitamin B12 may prevent age-related cognitive decline. The suggested daily dose is 100 mcg.

What Types of Drugs May Interact with Vitamin B12?

 • Drugs like omeprazole, ranitidine, colchicine, and metformin reduce the absorption of vitamin B12 through the intestines.