Criteria and recommendations for vitamin C intake.
Level 5 - mechanism / opinion, no new human data
Narrative review and expert guideline recommendation without original human trial data
PubMed 10217058 · doi:10.1001/jama.281.15.1415
What was done
The authors evaluated biochemical, molecular, pharmacokinetic, epidemiological, and clinical data across 9 criteria (dietary availability, plasma steady-state concentrations, tissue steady-state concentrations, bioavailability, urinary excretion, adverse effects, biochemical/molecular function, direct beneficial and epidemiologic effects, and deficiency prevention) to propose updated Dietary Reference Intake values for vitamin C.
What was found
Using an estimated average requirement (EAR) of 100 mg/d, the authors proposed an updated recommended dietary allowance (RDA) of 120 mg/d (up from the 1989 recommendation of 60 mg/d). They estimated adequate intake (AI) at 200 mg/d from 5 daily servings of fruits and vegetables, or 100 mg/d to prevent deficiency with a margin of safety. The tolerable upper intake level was proposed to be less than 1 g/d, noting potential adverse consequences at intakes of 1 g or more daily.
Why it matters
This paper provided a mechanistic and pharmacokinetic framework that shifted vitamin C intake recommendations from merely avoiding scurvy to optimizing plasma and tissue saturation for general health.
Limits
The abstract represents a narrative synthesis and policy proposal rather than a primary trial or systematic review. Specific sample sizes, individual study designs, effect sizes, and detailed risk profiles underlying the 1 g/d threshold are not detailed in the abstract.
Cited by
- supports Consuming five to nine servings of vitamin C-rich fruits and vegetables daily produces steady-state plasma vitamin C concentrations of around 80 micromoles per liter or less.
- contradicts A blood concentration of approximately 50 micromoles per liter of vitamin C is necessary to prevent the oxidation of LDL cholesterol.