Recommended dietary allowance for vitamins
Pro Research Analysisby 
Searched over 200M research papers
Recommended Dietary Allowance (RDA) Definition and Purpose
The Recommended Dietary Allowance (RDA) is defined as the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97–98%) healthy individuals in a particular life stage and gender group. The RDA is set to prevent deficiency symptoms and, more recently, to consider the potential for chronic disease prevention, although most current values are still based on deficiency prevention rather than optimal health outcomes 14.
RDA for Vitamin C: Current Recommendations and Debates
Standard RDA Values
The most recent US guidelines recommend an RDA for vitamin C of 90 mg/day for men and 75 mg/day for women, with a tolerable upper intake level (UL) of 2 g/day for adults . These values are slightly higher than previous recommendations, which were set at 60 mg/day for both men and women .
Arguments for Higher Vitamin C Intake
Several studies suggest that the current RDA for vitamin C may be too low to provide optimal health benefits beyond just preventing deficiency diseases like scurvy. Evidence indicates that intakes of 90–120 mg/day may be needed to reduce the risk of chronic diseases such as cancer, cardiovascular disease, and cataracts 27. Some researchers propose an RDA as high as 200 mg/day based on pharmacokinetic data showing that this dose achieves near-maximal plasma and tissue saturation without adverse effects 39. Others argue for even higher intakes, suggesting an optimal range of 250–4000 mg/day for best health, though this is not widely adopted in official guidelines .
Criteria for Setting Vitamin C RDA
Recommendations are based on factors such as dietary availability, plasma and tissue concentrations, bioavailability, urinary excretion, adverse effects, and epidemiological evidence. The tolerable upper intake level is generally set at less than 1 g/day to avoid potential adverse effects 79.
RDA for Vitamin E and Selenium
The RDA for vitamin E is set at 15 mg/day for both men and women, with a UL of 1 g/day for supplemental forms. For selenium, the RDA is 55 µg/day for adults, with a UL of 400 µg/day . No specific RDA is set for β-carotene and other carotenoids, but consumption of fruits and vegetables is recommended .
RDA for Vitamin D: Evolving Recommendations
Standard RDA Values
The Institute of Medicine (IOM) recommends an RDA for vitamin D of 600 IU/day for individuals aged 1–70 years and 800 IU/day for those over 70, aiming for a serum 25-hydroxyvitamin D level of at least 20 ng/mL (50 nmol/L) . These recommendations are based primarily on bone health outcomes, as evidence for other health benefits is inconsistent .
Controversies and Higher Intake Proposals
Recent analyses suggest that the RDA for vitamin D may have been underestimated due to statistical errors, with some researchers proposing much higher intakes—up to 2909 IU/day or more—to ensure that 97.5% of the population achieves adequate serum levels 510. Body weight also affects vitamin D requirements, with higher doses needed for overweight and obese individuals . However, there is concern about the risks of both low and high serum vitamin D concentrations, and some experts recommend an approach that minimizes these risks rather than a single RDA value .
Critiques and Calls for RDA Redefinition
Some researchers argue that the current RDA concept, developed in 1941, may not be optimal for all nutrients or populations. They suggest that RDAs should be redefined based on prospective studies linking intake levels to disease incidence and mortality, rather than just deficiency prevention .
Conclusion
The RDAs for vitamins are designed to prevent deficiency in nearly all healthy individuals, but there is ongoing debate about whether current values are sufficient for optimal health, especially for vitamins C and D. While official guidelines provide specific intake levels, emerging research suggests that higher intakes may be beneficial for some individuals and that recommendations may need to be tailored based on new evidence and individual factors such as body weight.
Sources and full results
Most relevant research papers on this topic