What oral vitamin C dose is recommended for a generally healthy adult without renal disease, kidney stones, or glucose‑6‑phosphate dehydrogenase deficiency?

Oral Vitamin C Dosing for Healthy Adults

For a generally healthy adult without renal disease, kidney stones, or G6PD deficiency, the recommended daily oral vitamin C intake is 75–90 mg/day (women and men, respectively) to prevent deficiency, but an optimal intake of approximately 200 mg/day achieves tissue saturation and maximizes health benefits without added risk. 1

Standard Recommended Daily Allowances

The baseline recommendations vary slightly by authority but cluster around similar values:

• 75 mg/day for women and 90 mg/day for men according to the National Institutes of Health 1
• 95 mg/day for women and 110 mg/day for men per the European Food Safety Authority 1
• International recommendations range from 40–220 mg/day depending on whether the goal is preventing scurvy versus optimizing tissue saturation versus reducing chronic disease risk 1

The minimum threshold of 40–45 mg/day prevents scurvy but does not achieve tissue adequacy 1. This distinction is critical: meeting the RDA prevents deficiency disease but may not optimize antioxidant protection, immune function, or cardiovascular benefits.

Optimal Intake: The 200 mg/day Threshold

The preponderance of evidence supports 200 mg/day as the optimal intake for most healthy adults, achieving near-complete tissue saturation with plasma levels around 70 µmol/L 1. This level:

• Maximizes potential health benefits including antioxidant protection, immune support, and modest cardiovascular risk reduction 1
• Can be readily obtained from diet alone with ≥5 servings of fruits and vegetables, including at least one high-vitamin C source 1
• Represents the point at which intestinal absorption saturates; plasma concentrations plateau at intakes of roughly 200–400 mg/day, with no further rise at 1000 mg/day 1

A meta-analysis demonstrated significant reductions in systolic and diastolic blood pressure with a median vitamin C intake of 500 mg/day, suggesting measurable cardiovascular benefit at doses above the RDA 1. However, randomized controlled trials provide little evidence that intakes >200 mg/day improve mortality or major morbidity outcomes in healthy individuals 1.

Higher Doses: Diminishing Returns and Safety

Doses of 1000 mg/day are safe but unlikely to add benefit beyond the 200 mg threshold for mortality, morbidity, or quality-of-life outcomes 1. Key considerations:

• The Tolerable Upper Intake Level (UL) is 2000 mg/day, indicating that 1000 mg/day is well within the established safety margin 1, 2
• At 1000 mg/day, the most common adverse effect is gastrointestinal disturbance (mild diarrhea) due to osmotic effects of unabsorbed vitamin C, though this occurs infrequently at this dose 1
• Intestinal absorption saturates at higher oral doses; consequently, a large proportion of a 1000 mg dose is not absorbed 1
• The additional 800 mg beyond 200 mg does not confer documented improvements in clinical outcomes for healthy adults 1

Special Populations Requiring Higher Intake

Certain groups have elevated requirements:

• Smokers require an extra 35 mg/day above baseline needs due to elevated oxidative stress and vitamin C turnover 1, 3
• Obesity may blunt the response to supplementation, potentially increasing vitamin C requirements; a 1000 mg/day regimen may be more appropriate in this population 1
• Patients with chronic oxidative stress may require 200–500 mg/day 1

Practical Algorithm for Dosing

1. Target 200 mg/day total vitamin C (diet + supplement) as the evidence-based optimal level for healthy adults 1
2. Prefer dietary sources over high-dose supplements when possible, as whole foods provide additional beneficial phytochemicals 1
3. If currently taking 1000 mg/day, recognize that it is safe but unlikely to add benefit beyond the 200 mg threshold; reducing to 200 mg/day can avoid unnecessary expense and improve absorption efficiency without compromising health outcomes 1
4. Do not exceed 2000 mg/day to avoid higher risk of diarrhea and other gastrointestinal disturbances 1, 2

Common Pitfalls

• Overestimating benefit of megadoses: Many intervention studies are methodologically limited because participants often start near tissue saturation and placebo groups continue background supplementation up to the RDA, obscuring incremental effects 1
• Ignoring dietary sources: The optimal 200 mg/day can be achieved through diet alone with adequate fruit and vegetable intake, making supplementation unnecessary for many individuals 1
• Confusing safety with efficacy: While doses up to 2000 mg/day are generally safe, safety does not imply additional clinical benefit above the saturation threshold 1, 2