Vitamin C C deficiency. Beyond that, a role for vitamin C as prevention or treatment for various diseases is disputed, with reviews reporting conflicting results. A 2012 Cochrane review reported no effect of vitamin C supplementation on overall mortality. It is on the World Health Organization's List of Essential Medicines as one of the most effective and safe medicines needed in a health system. The disease scurvy is caused by vitamin C deficiency and can be prevented and treated with vitamin C-containing foods or dietary supplements. It takes at least a month of little to no vitamin C before symptoms occur. Early
Vitamin B12 deficiency those with low levels due to absorption problems. When large doses are given by mouth its absorption does not rely on the presence of intrinsic factor or an intact ileum. Generally 1 to 2 mg daily is required as a large dose. Even pernicious anemia can be treated entirely by the oral route. These supplements carry such large doses of the vitamin that 1% to 5% of high oral doses of free crystalline B is absorbed along the entire intestine by passive diffusion. Vitamin B deficiency is quite common and widespread. In the US and UK, as around 6 percent