Vitamin B12 can be stored in the body, and a deficiency will only become apparent 5 years after all the vitamin B12 stored in the body has been depleted, whereas it takes up to 3 years for all the vitamin B12 stored in the body to be consumed. Therefore, the body does not easily become deficient in vitamin B12

However, malabsorption can lead to vitamin B12 deficiency, which is most common in the elderly and those with digestive disorders. Vegetarians are also more susceptible to vitamin B12 deficiency, the symptoms of which include walking deformities, memory loss, delusions of grandeur, eye problems, anemia, and indigestion. Vitamin B12 deficiency can also cause mouth ulcers, nervousness, back pain, mobility difficulties, and in severe cases, spinal cord degeneration and paralysis.

Generally, a person's diet only lacks vitamin B12, will not cause anemia, and if at the same time the lack of vitamin B12 folic acid and other B vitamins, will cause pernicious anemia.