Some is made in the body. Deficiency leads to pellagra. High doses cause dilation of arteries and reduction of blood lipids. Excess can cause kidney damage. B 12 Is necessary for the proper formation of blood cells and nerve fibres.
Rich sources are offal and meat.
Eggs and milk also contain B 12 . Almost no plant foods contain B 12 . Fortified breakfast cereals are a useful source. Deficiency leads to pernicious anaemia. No toxic effects known.