Known as the "red vitamin" and often called the "energy vitamin," B12 is unique: it is the only vitamin that contains a mineral – cobalt; it is the only B vitamin not utilized from plant foods; and since the body stores vitamin B12 (unlike the other B vitamins), it is required in much smaller amounts than other B vitamins (only 3-4 mcg are needed).
The "energy vitamin" is essential for the formation of normal red blood cells and for the health of the entire nervous system. Fatigue is usually the first sign of B12 deficiency. Dizziness, excessive sleep, depression, nerve damage, anemia, and dementia are among the many signs and symptoms that may follow if levels of vitamin B12 do not improve. When deficient for long periods, a condition called pernicious anemia develops.
Although cobalamin is manufactured by bacteria in a healthy intestinal tract, a mucoprotein enzyme produced by the stomach's parietal cells (known as the "intrinsic factor") is needed for vitamin B12 absorption. The intrinsic factor requires hydrochloric acid from the stomach. Individuals with weak acid production (a result of poor digestion, overuse of antacids, overeating, stress, stomach surgery, aging, or other factors) may become deficient in vitamin B12.
The only significant food sources of vitamin B12 are animal foods. Meat, fish, eggs, and dairy products are excellent sources. Though fermented foods may contain small amounts, it is not known how much is actually absorbed; thus, vegans must supplement with vitamin B12. The supplemental form is sold as cyanocobalamin. Taken sublingually (allowing a tablet to dissolve under the tongue), 10-20 mcg daily is recommended for adults.