Vitamin B₁₂ deficiency

Vitamin B₁₂ deficiency, also known as cobalamin deficiency, is the medical condition in which the blood and tissues have a lower than normal level of vitamin B₁₂.

Mild deficiencies may have few or absent symptoms. In moderate deficiencies, feeling tired, feeling faint, mouth ulcers, rapid breathing, upset stomach, pallor, hair loss, decreased ability to think and joint pain and the beginning of neurological symptoms, including abnormal sensations such as, numbness and tingling, and tinnitus may occur. Severe deficiencies may include symptoms of reduced heart function, suppression of bone marrow, as well as more various severe neurological symptoms possibly including sensory loss, abnormal balance and reflexes, memory and consciousness impairment, smell and taste problems, depression, irritability, confusion, and psychosis. If left untreated, some of these changes can become permanent. Onset of deficiency may take years to develop. In exclusively breastfed infants of vegan mothers, undetected and untreated deficiency can lead to poor growth, poor development, and difficulties with movement.

In healthy adults, vitamin B₁₂ deficiency is not common, mainly because body stores of the vitamin are substantial and turnover is slow, with relatively low dietary requirements. Risk factors may occur possibly more in elderly people due to impaired intestinal absorption, children, premenopausal women, and pregnant women, whose diets are low in animal foods.

Causes are usually related to conditions that give rise to malabsorption of vitamin B₁₂, particularly autoimmune gastritis in pernicious anemia. Other conditions giving rise to malabsorption include surgical removal of the stomach, chronic inflammation of the pancreas, intestinal parasites, certain medications such as long-term use of proton pump inhibitors, H2-receptor blockers, and metformin, and some genetic disorders. Deficiency can also be caused by inadequate dietary intake such as with the diets of vegetarians, and vegans, and in the malnourished. Elevated methylmalonic acid levels may also indicate a deficiency.

Treatment is by vitamin B₁₂ supplementation, either by mouth or by injection. If no reversible cause is found, or when found it cannot be eliminated, lifelong vitamin B₁₂ administration is usually recommended. Vitamin B₁₂ deficiency is preventable with supplements, which are recommended for pregnant vegetarians and vegans, and not harmful in others.

Vitamin B₁₂ deficiency in the US and the UK is estimated to occur in about 6 percent of those under the age of 60, and 20 percent of those over the age of 60. In Latin America, about 40 percent are estimated to be affected, and this may be as high as 80 percent in parts of Africa and Asia. Marginal deficiency is much more common and may occur in up to 40% of Western populations.