For practical reasons, the RDA for any nutrient is defined as "the level of intake necessary to meet the needs of all healthy people". For example, the RDA for Vitamin C only indicates the amount required by a person to prevent scurvy. It does not reflect the body's total need of the vitamin because it omits the numerous metabolic functions that require Vitamin C. It also fails to take into account the optimal amount required for it to serve as an effective anti-oxidant.
Unlike certain animals that can synthesise Vitamin C in their own bodies, the human body does not have such ability. Therefore, the RDA may not be effective to fulfill all the bodily requirements. Moreover, a person's need for Vitamin C dramatically increase given today's heavily polluted environment or when the person is a smoker, under stress or ill. For example, sick people require 20 - 40 times more Vitamin C. In addition, other factors such as age, body size, health status and biochemical factors in the body also affect the amount of Vitamin C required.
Dr Linus Pauling, a two-time Nobel Prize Winner has, after years of research and experiences, advocated a daily intake of 1 - 3g (1000 - 3000mg) of Vitamin C for the prevention of an illness, while 8 - 10g (8000 - 10000mg) would be required to cure an existing illness. Recent mounting evidence has lent support to his claim.