An untreated vitamin B-12 deficiency carries the risk of serious or permanent nerve damage, resulting in symptoms such as memory loss or numbness and tingling in hands and feet, Drugs.com explains. Other symptoms of nerve damage may include muscle weakness, difficulty walking, irritability and dementia.
Studies have shown that seniors over age 65 have a greater risk of developing brain shrinkage and cognitive decline if they are deficient in vitamin B-12, Medical News Today states.
In some cases, neurological damage from a deficiency can also trigger psychiatric symptoms, such as psychosis and depression, according to Drugs.com. Vitamin B-12 is necessary for the body to produce healthy red blood cells. The deficiency typically develops in people who don't consume enough animal products or people who have pernicious anemia, which prevents adequate absorption of vitamin B-12.