What is the recommended daily intake of vitamin C (ascorbic acid) for an adult?

Recommended Daily Vitamin C Intake for Adults

Adults should consume 75-90 mg of vitamin C daily (75 mg for women, 90 mg for men), with European authorities recommending slightly higher amounts of 95-110 mg daily. 1

Standard Recommendations by Authority

The recommended daily intake varies by regulatory body, reflecting different underlying health perspectives:

• United States (NIH): 75 mg/day for women and 90 mg/day for men 1
• European Food Safety Authority (EFSA): 95 mg/day for women and 110 mg/day for men 2, 1
• Germany, Austria, Switzerland (DACH): 95 mg/day for women and 110 mg/day for men 3

These recommendations are based on maintaining adequate plasma vitamin C concentrations (≥50 µmol/L) and replacing daily metabolic losses, rather than merely preventing scurvy. 2, 3

Understanding the Range of Global Recommendations

A critical pitfall is confusing scurvy prevention with optimal health. International recommendations range from 40-220 mg/day because different authorities use fundamentally different criteria: 2

• Minimum threshold (40-45 mg/day): Prevents scurvy but does not ensure tissue adequacy 2, 1
• Adequate intake (75-110 mg/day): Maintains plasma concentrations and replaces daily turnover 2, 1, 3
• Optimal intake (200+ mg/day): Some evidence suggests higher intakes may reduce chronic disease risk, though this remains debated 4

Practical Dietary Implementation

Five servings of fruits and vegetables daily will meet vitamin C requirements for most healthy adults. 1, 5

• One 150 ml glass of unsweetened orange juice contributes significantly to daily needs 2, 6
• Dietary sources should always be the first-line approach before considering supplementation 6
• Absorption from food is more reliable than supplements at higher doses due to saturable intestinal transporters 1

Special Populations Requiring Higher Intake

Certain groups need increased vitamin C beyond standard recommendations:

• Smokers: 110-135 mg/day for women and 125-155 mg/day for men (40% higher turnover) 3
• Pregnant women: 105 mg/day from the fourth month onward 3
• Lactating women: 125 mg/day 3
• Older adults: 95 mg/day minimum, with supplementation only if dietary intake is poor 2, 6

When Supplementation May Be Appropriate

Supplementation should be reserved for documented inadequate dietary intake, not used routinely. 6

• Consider supplementation only when dietary modification fails or is not feasible 6
• The tolerable upper limit is 2000 mg/day based on gastrointestinal upset 5, 7
• Oral absorption becomes saturated at higher doses, limiting effectiveness of mega-dosing 1

Clinical Scenarios Requiring Substantially Higher Doses

These are distinct from routine supplementation and require medical supervision:

• Critically ill patients: 2-3 g/day IV during acute inflammation 1
• Continuous renal replacement therapy: 2-3 g/day IV 1
• Cardiac surgery patients: 1-2 g/day IV for 5-7 days 1
• Chronic oxidative stress: 200-500 mg/day 1

Important caveat: IV administration is necessary in critical illness because enteral absorption is unpredictable and plasma levels drop precipitously during inflammation. 1, 8

Monitoring Considerations

Do not measure plasma vitamin C during acute illness or inflammation—results are unreliable. 1

• Testing is only recommended for suspected scurvy or chronic low intake 1
• Plasma levels decrease when C-reactive protein exceeds 10 mg/L 1, 8
• Normal vitamin C values are typically undetectable when CRP exceeds 40 mg/L 1

Key Algorithmic Approach for Clinical Practice

1. Assess dietary intake: Does the patient consume 5 servings of fruits/vegetables daily? 6, 5
2. If adequate diet: No supplementation needed for healthy adults 1, 6
3. If inadequate diet: Provide dietary counseling first 6
4. If dietary modification fails: Consider 75-110 mg/day supplementation 1, 6
5. Special populations: Adjust upward per guidelines above 3
6. Critical illness: Requires IV administration at gram doses under medical supervision 1

The fundamental principle is that 75-110 mg/day meets physiologic needs for healthy adults, achievable through diet alone, with supplementation reserved for specific deficiency states or clinical scenarios—not for routine health optimization in well-nourished individuals. 1, 5, 7