Vitamin C Administration Guidelines
Recommended Daily Intake for Healthy Individuals
For general health maintenance in adults, the recommended daily intake is 75 mg/day for women and 90 mg/day for men according to US guidelines, though European authorities recommend slightly higher amounts at 95 mg/day for women and 110 mg/day for men. 1, 2
Standard Oral Dosing by Population
- Women: 75 mg/day (US) or 95 mg/day (Europe) 1, 2
- Men: 90 mg/day (US) or 110 mg/day (Europe) 1, 2
- Minimum to prevent scurvy: 40-45 mg/day 1, 2
- Smokers: Add 35 mg/day to baseline recommendations 3
- Pregnant/lactating women: Should not exceed US RDA without medical supervision 4
Key Distinction: Minimum vs. Optimal
The wide range of international recommendations (40-220 mg/day) reflects different health perspectives: preventing scurvy versus optimizing tissue saturation versus reducing chronic disease risk. 2 The 40-45 mg/day threshold prevents scurvy but does not necessarily achieve tissue adequacy. 2
Intravenous Vitamin C Administration
FDA-Approved Indication (ASCOR)
IV vitamin C is FDA-approved exclusively for short-term treatment (up to 1 week maximum) of scurvy when oral administration is not possible, insufficient, or contraindicated. 4
FDA-Approved Dosing for Scurvy Treatment
- Infants 5-12 months: 50 mg once daily IV 4
- Children 1-11 years: 100 mg once daily IV 4
- Adults and children ≥11 years: 200 mg once daily IV 4
- Maximum duration: 1 week 4
Critical Preparation Requirements (FDA Label)
- Must be diluted before administration - undiluted ASCOR has osmolarity ~5,900 mOsmol/L and will cause severe adverse reactions 4
- Dilute to final concentration of 1-25 mg/mL in isotonic solution (5% Dextrose or Sterile Water with appropriate solutes) 4
- Administer as slow IV infusion, not bolus 4
- Light-sensitive: minimize light exposure 4
- Pharmacy Bulk Package must be used within 4 hours of puncture 4
- Do not mix with solutions containing reducible elements (e.g., copper) 4
Higher-Dose IV Protocols for Critical Illness (Off-Label)
ESPEN Guideline Recommendations
For critically ill patients with documented severe deficiency or specific clinical scenarios, higher IV doses may be considered, though this is distinct from routine sepsis treatment. 1, 5
- Acute inflammation phase: 2-3 g/day IV (Grade B, 84% consensus) 1, 5
- Continuous renal replacement therapy: 2-3 g/day IV 1, 5
- Cardiac surgery (perioperative): 1-2 g/day IV for 5-7 days 1, 5
- Chronic oxidative stress/malabsorption: 200-500 mg/day 1
Important Context on Sepsis
Do NOT routinely use vitamin C for sepsis treatment - the Surviving Sepsis Campaign pediatric guidelines (2020) recommend against ascorbic acid for septic shock (weak recommendation, very low quality evidence). 6 The C-EASIE 2025 trial using 1.5 g IV every 6 hours for 4 days showed no significant benefit (SOFA score ratio 0.91,95% CI 0.77-1.08, P=0.30). 6
Safety Considerations and Contraindications
Absolute Contraindications for High-Dose Vitamin C
- Hemochromatosis (iron overload) 6, 5
- G6PD deficiency (risk of hemolysis) 6, 5, 4
- Active oxalate kidney stones 6, 5
- Severe renal dysfunction (without CRRT) 6, 5
Tolerable Upper Limit
The tolerable upper intake level is 2 g/day orally based on gastrointestinal upset (diarrhea, nausea) at higher doses. 3, 7 However, IV administration bypasses GI limitations. 1
Special Populations Requiring Caution
Pregnant women, lactating women, and patients with G6PD deficiency should not exceed the US RDA without documented deficiency. 4
Monitoring and Laboratory Testing
When to Measure Plasma Levels
- Suspected scurvy with clinical signs (petechiae, bleeding gums, poor wound healing) 1, 5
- Chronic low intake in high-risk populations 1, 5
When NOT to Measure Plasma Levels
Do not measure plasma vitamin C during acute inflammation or critical illness - levels decline rapidly when CRP >10 mg/L, and normal values are not detected if CRP >40 mg/L, making interpretation unreliable. 1, 6, 5
Common Pitfalls to Avoid
Oral Administration Limitations
Oral absorption is saturable - intestinal transporters limit uptake at doses >200 mg, with bioavailability decreasing significantly at higher oral doses. 1 In critical illness, enteral uptake is unpredictable due to impaired gut function. 5
IV Administration Errors
- Never administer undiluted ASCOR - this is the most dangerous error and can cause severe osmotic injury 4
- Do not confuse the 25,000 mg bulk vial with a single-patient dose (maximum single dose is 200 mg for scurvy) 4
- Samples require special handling for accurate measurement (light-sensitive, oxidizes rapidly) 1
Clinical Decision-Making Errors
- Do not delay standard sepsis care (antibiotics, source control, fluids, vasopressors) to administer vitamin C 6
- Do not use vitamin C as monotherapy antioxidant in high doses without proven severe deficiency (Grade B, 96% consensus) 6
- Sustained therapy is needed to prevent recurrence of hypovitaminosis - single doses are insufficient 5