What are the indications and dosing recommendations for Vitamin C (Ascorbic Acid)?

Vitamin C Indications and Dosing

Vitamin C is indicated for prevention and treatment of scurvy, with additional higher doses recommended for specific clinical conditions including chronic oxidative stress states, critical illness, and malabsorption syndromes.

Primary Indications

Prevention and Treatment of Scurvy

• Scurvy prevention requires a minimum of 40-45 mg/day, though this only prevents deficiency disease and does not represent optimal intake 1, 2
• For suspected or confirmed scurvy, administer 1 g/day orally for at least one week without delay 1
• Clinical diagnosis should not be delayed waiting for laboratory confirmation, as plasma vitamin C levels reflect recent dietary intake rather than tissue stores 3
• Pathognomonic findings include perifollicular hemorrhages, "corkscrew" hair, ecchymoses, and gingival bleeding 3

General Health Maintenance

• Healthy adults: 75-90 mg/day (women/men respectively) per NIH recommendations 2
• European recommendations are higher: 95-110 mg/day (women/men) 1, 2
• Smokers require an additional 60-140 mg/day above baseline requirements due to increased oxidative stress 4

Clinical Conditions Requiring Higher Doses

Chronic Oxidative Stress States

Administer 200-500 mg/day for patients with: 1

• Diabetes mellitus
• Heart failure
• Chronic obstructive pulmonary disease (severe)
• Alcoholism
• Chronic hemodialysis
• Active smoking

This recommendation carries a Grade GPP with 92% consensus 1

Critical Illness and Acute Inflammation

During critical illness, administer 2-3 g/day IV during the acute phase of inflammation 1, 2

• This is a Grade B recommendation with 84% consensus 1
• Oral absorption is unreliable in critical illness; IV administration is necessary 2
• Plasma levels decline rapidly when CRP >10 mg/L, making oral supplementation inadequate 1

Continuous Renal Replacement Therapy (CRRT)

• Administer 2-3 g/day IV to replace dialysis losses 1, 5
• Daily effluent losses approximate 68 mg 5
• However, for chronic hemodialysis patients NOT in acute illness, limit to 100 mg/day to avoid oxalate accumulation 5

Perioperative Cardiac Surgery

• Administer 1-2 g/day IV for 5-7 days perioperatively 1
• This carries Level 1+ evidence 1

Parenteral Nutrition

• Standard PN dosing: 100-200 mg/day 1

Malabsorption Syndromes

• Post-bariatric surgery: 200-500 mg/day may be required 1
• Chronic malabsorption conditions require similar dosing 1

Sepsis: Important Caveat

Do NOT routinely administer vitamin C for sepsis treatment 6

• The Surviving Sepsis Campaign recommends against ascorbic acid use in pediatric septic shock (weak recommendation, very low quality evidence) 6
• The C-EASIE 2025 trial using 6 g/day showed no significant benefit (SOFA score ratio 0.91,95% CI 0.77-1.08, P=0.30) 6
• Consider vitamin C in sepsis ONLY in the context of documented severe deficiency, research protocols, or refractory shock after exhausting all guideline-recommended therapies 6
• Never delay standard sepsis care (antibiotics, source control, fluids, vasopressors) to administer vitamin C 6

Monitoring and Laboratory Testing

When to Measure Plasma Levels

• Measure plasma vitamin C in patients with clinical suspicion of scurvy or chronic low intake 1, 2
• Do NOT measure during critical illness or when CRP >10 mg/L - levels are unreliable and difficult to interpret 1, 2
• Normal values are not detected when CRP >40 mg/L 2

Sample Handling

• Vitamin C samples require special handling for accurate measurement 2
• Laboratory testing is not necessary to confirm scurvy if clinical findings are present 3

Special Populations and Contraindications

Renal Impairment

For CKD Stage 1-4 (not on dialysis): limit total vitamin C to 100 mg/day from all sources 5

• Excessive intake causes oxalate accumulation in plasma and soft tissues 5
• Pediatric dialysis patients require lower doses (15 mg/day supplement if receiving 140% RDA from diet) 5

Absolute Contraindications for High-Dose Vitamin C

Avoid high-dose supplementation in: 2, 6

• Hemochromatosis or iron overload states
• G6PD deficiency
• Active oxalate kidney stones
• Severe renal dysfunction (except during CRRT in critical illness)

Common Pitfalls to Avoid

1. Oral absorption is saturable - intestinal transporters become saturated at higher doses, making IV administration necessary for repletion in critical illness 2

2. Inflammation falsely lowers plasma levels - do not interpret low vitamin C levels during acute illness as indicating need for supplementation unless there is clinical scurvy 1

3. Confusing maintenance with repletion dosing - chronic conditions require 200-500 mg/day, while acute critical illness requires 2-3 g/day IV 1

4. Using vitamin C as sepsis therapy - this is not evidence-based and should not delay standard care 6

5. Overlooking scurvy in at-risk populations - alcoholics, elderly with poor nutrition, psychiatric patients, and low socioeconomic status individuals are at highest risk 3