vitamin B12

A complex water-soluble vitamin containing cobalt. Vitamin B₁₂ can be obtained from liver, fish, and some dairy products. It is the only member of the B complex that cannot be obtained from yeast. Vitamin B₁₂ acts as a coenzyme. It is involved in DNA synthesis and the formation of red blood cells. Vitamin B₁₂ and folic acid interact: deficiency of B₁₂ leads to functional deficiency of folic acid. In addition, a glycoprotein (known as intrinsic factor) produced by the stomach is needed for absorption of Vitamin B₁₂ across the membrane of the intestine into the bloodstream. Lack of B₁₂, or intrinsic factor, or folic acid, may cause pernicious anaemia and weight loss. Vitamin B₁₂ is regarded as an ergogenic aid by many coaches who believe it improves energy metabolism in muscle cells. Supplementation, often by injection into the buttocks, is common even though most research has shown no significant benefits where a B₁₂ deficiency does not exist. Toxic effects of vitamin B₁₂ are virtually unknown, but allergic reactions occasionally occur from injections. In the UK, the Reference Nutrient Intake for adults is 1.5 micrograms per day.