The recommended dietary allowance (RDA) for vitamin C differs greatly (40-110 mg/d) across countries. In addition, vitamin D deficiency is, effectively, a pandemic, with a prevalence of approximately 25% to 80% across countries according to the findings in the recent scientific literature. However, these phenomena are attributable to a serious error in the concept and definition of RDA, which was developed in 1941. The current definition of RDA is the average daily dietary nutrient intake level that is deemed sufficient to meet the nutrient requirements of almost all (97-98%) healthy individuals. This is an extremely high intake level for a specific nutrient affecting only a few individuals (the upper 2.5%) of the generally healthy population. The RDA should be redefined by investigating at which intake level of a specific nutrient the incidence of a specific disease or mortality increases or decreases based on prospective cohort studies.