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 vitamin B. Elevated methylmalonic acid levels may also indicate a deficiency. A type of anemia known as megaloblastic anemia is often but not always present. Treatment consists of using vitamin B by mouth or by injection; initially in high daily doses, followed by less frequent lower doses as the condition improves. If a reversible cause is found, that cause should be addressed if possible. If no reversible cause is found - or when found it cannot be eliminated - lifelong vitamin B supplementation is usually recommended. Vitamin B deficiency is preventable with supplements containing the vitamin: this is recommended in