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 A deficiency Supplement treatment for night blindness includes massive doses of vitamin A (200,000 IU) in the form of retinyl palmitate to be taken by mouth, which is administered two to four times a year. Intramuscular injections are poorly absorbed and are ineffective in delivering sufficient bioavailable vitamin A. Fortification of food with vitamin A is costly, but can be done in wheat, sugar, and milk. Households may circumvent expensive fortified food by altering dietary habits. Consumption of yellow-orange fruits and vegetables rich in carotenoids, specifically beta-carotene, provides provitamin A precursors that can prevent VAD-related night blindness. However, the conversion of carotene