What is the recommended daily dose of ascorbic acid (Vitamin C) for an adult?

Recommended Daily Dose of Ascorbic Acid (Vitamin C) for Adults

For healthy adults, the recommended daily intake of vitamin C is 75-90 mg/day (75 mg for women, 90 mg for men), with European authorities recommending slightly higher doses of 95-110 mg/day. 1

Standard Dosing by Region and Authority

Global recommendations vary substantially based on different health objectives:

• United States/Canada: 90 mg/day for men and 75 mg/day for women, based on maintaining near-maximal neutrophil concentrations to provide antioxidant protection 2
• European Union (EFSA/DACH): 110 mg/day for men and 95 mg/day for women, the highest standard recommendations globally, based on maintaining adequate body pool with fasting plasma ascorbate concentrations around 50 µmol/L 2
• United Kingdom/Australia/India/FAO-WHO: 40-45 mg/day, based solely on preventing scurvy (deficiency disease) 2
• Japan/Nordic countries: 75-100 mg/day, considering antioxidant effects and cardiovascular disease prevention 2

The nearly three-fold variation in recommendations (40-110 mg/day) reflects fundamentally different approaches: preventing deficiency versus optimizing tissue saturation versus reducing chronic disease risk. 2

Clinical Scenarios Requiring Higher Doses

Chronic oxidative stress conditions (diabetes, heart failure, smoking, alcoholism, severe COPD, chronic dialysis): 200-500 mg/day 2, 1

Pregnancy: Add 10-20 mg/day to baseline recommendation 2

Lactation: Add 20-60 mg/day to baseline recommendation 2

Post-bariatric surgery: 200-500 mg/day may be required long-term 2, 1

Critical illness/acute inflammation: 2-3 g/day IV during acute phase (Grade B recommendation, 84% consensus) 2, 1

Continuous renal replacement therapy (CRRT): 2-3 g/day IV to replace losses 2, 1, 3

Cardiac surgery (periprocedural): 1-2 g/day IV for 5-7 days 2, 1

Important Clinical Considerations

Absorption limitations: Oral vitamin C absorption is limited at higher doses due to saturation of intestinal transporters, making IV administration necessary in critical illness where enteral uptake is unpredictable. 1, 4

Renal impairment: Patients with kidney disease should limit total vitamin C to 100 mg/day from all sources to avoid oxalate accumulation, which can be dangerous in renal dysfunction. 3 The exception is patients on CRRT during critical illness, who require 2-3 g/day IV to replace dialysis losses. 3

Monitoring pitfalls: Plasma vitamin C levels should only be measured in patients with suspected scurvy or chronic low intake, NOT during critical illness or inflammation (CRP >10 mg/L), as levels decline rapidly and become uninterpretable. 2, 1 Normal values are not detected when CRP >40 mg/L. 2

Treatment of deficiency: When clinical symptoms suggest scurvy (bleeding gums, petechiae, poor wound healing, perifollicular hemorrhages), initiate treatment immediately with 100 mg three times daily (300-500 mg/day total) for at least one month without waiting for laboratory confirmation. 1

Practical Algorithm for Dosing

1. Healthy adults: 75-90 mg/day (or 95-110 mg/day per European guidelines) 1
2. Smokers, diabetics, heart failure, COPD, dialysis patients: 200-500 mg/day 2, 1
3. Pregnant women: Add 10-20 mg/day 2
4. Lactating women: Add 20-60 mg/day 2
5. Critically ill with inflammation: 2-3 g/day IV 2, 1
6. Renal impairment (not on dialysis): Maximum 100 mg/day 3
7. Suspected scurvy: 300-500 mg/day orally, start immediately 1

The minimum 40-45 mg/day prevents scurvy but does not achieve tissue adequacy or provide antioxidant benefits, making the higher US/European recommendations more appropriate for optimal health. 2, 1