Recommended Daily Vitamin C Intake and Effects
For healthy adults, consume 90-110 mg of vitamin C daily, which can be easily achieved through 5 servings of fruits and vegetables per day, with higher amounts (up to 2,000 mg/day) generally safe but offering unclear additional benefits for most people. 1
Standard Recommended Daily Intake
The recommended daily allowance varies by regulatory authority but clusters around similar values:
- United States (NIH): 90 mg/day for men, 75 mg/day for women 1, 2
- European Food Safety Authority: 110 mg/day for men, 95 mg/day for women 1, 2
- Germany, Austria, Switzerland: 110 mg/day for men, 95 mg/day for women 3
These recommendations are based on maintaining adequate plasma vitamin C levels (≥50 µmol/L) and replacing daily metabolic losses, not merely preventing scurvy 3. The minimum intake to prevent scurvy is only 40-45 mg/day, which represents an outdated criterion that some countries still use 2.
Populations Requiring Higher Intake
Smokers need substantially more vitamin C due to 40% higher metabolic turnover:
- 155 mg/day for male smokers
- 135 mg/day for female smokers 3
Pregnant and lactating women have increased requirements:
Post-bariatric surgery patients should ensure adequate intake, with vitamin C supplementation considered concurrently with iron supplements to improve iron absorption 2.
Clinical Scenarios Requiring Pharmacologic Doses
Beyond nutritional requirements, certain medical conditions may warrant higher therapeutic doses under medical supervision:
- Chronic oxidative stress: 200-500 mg/day 1
- Critical illness/sepsis: 2-3 g/day IV 1
- Cardiac surgery: 1-2 g/day IV for 5-7 days 1
- Continuous renal replacement therapy: 2-3 g/day IV 1
Note that oral absorption becomes saturated at higher doses due to intestinal transporter limitations, making IV administration necessary in critical illness 1.
Safety and Upper Limits
The Tolerable Upper Intake Level is 2,000 mg/day for adults, representing the highest intake unlikely to cause adverse effects in most individuals 4, 5. Doses above this threshold may cause gastrointestinal upset 5.
Special Precautions
Patients with iron overload conditions (hemochromatosis) should avoid vitamin C supplementation, particularly during iron depletion treatment, as vitamin C enhances iron absorption 4.
Practical Dietary Sources
Foods rich in vitamin C include citrus fruits (oranges, lemons, limes), tomatoes, and potatoes 6. Five servings of fruits and vegetables daily provides approximately 200 mg of vitamin C, exceeding the RDA and potentially offering disease prevention benefits 7.
Key Clinical Pitfalls
- Don't rely on plasma levels during inflammation: Vitamin C levels decrease when C-reactive protein >10 mg/L and are typically undetectable when CRP >40 mg/L 1
- Testing is rarely indicated: Reserve testing only for suspected scurvy or documented chronic low intake 1
- Vitamin C samples require special handling for accurate measurement 1
- Oral supplementation has limited absorption at doses exceeding 200-500 mg due to transporter saturation 1
Health Effects Beyond Deficiency Prevention
While the primary established benefit is scurvy prevention (which occurs at plasma levels <0.15 mg/dL), vitamin C functions as:
- A reducing agent essential for collagen synthesis through hydroxylation of proline and lysine 6
- An antioxidant protecting against free radical damage 6, 5
- A cofactor with antiviral and antibacterial activity supporting leukocyte phagocytic function 8
Scurvy manifestations include weakness, joint pain, petechiae, gum bleeding, easy bruising, delayed wound healing, and characteristic perifollicular hyperkeratotic papules with kinky hair 6.
Human vitamin C stores are minimal compared to fat-soluble vitamins—deficiency can manifest within weeks and prove fatal in 5-6 months without intake 5.