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Vitamin C (Ascorbic Acid)

SI UNITS (recommended)

CONVENTIONAL UNITS

(Essential Water-Soluble Antioxidant - Required for Collagen Synthesis, Immune Function & Iron Absorption)

Synonyms

  • Ascorbic acid
  • Vitamin C
  • L-ascorbate
  • Dehydroascorbic acid (oxidized form)
  • Anti-scurvy vitamin

Units of Measurement

  • µmol/L
  • mg/L
  • mg/dL
  • mg/100 mL
  • mg%
  • µg/mL

Unit Conversions

Molecular Weight of Ascorbic Acid = 176.12 g/mol

µmol/L ↔ mg/L

1 µmol/L=0.176 mg/L1\ \text{µmol/L} = 0.176\ \text{mg/L}1 µmol/L=0.176 mg/L 1 mg/L=5.67 µmol/L1\ \text{mg/L} = 5.67\ \text{µmol/L}1 mg/L=5.67 µmol/L

mg/dL → mg/L

1 mg/dL=10 mg/L1\ \text{mg/dL} = 10\ \text{mg/L}1 mg/dL=10 mg/L

µg/mL → mg/L

1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L

mg/100 mL = mg% = mg/dL

Description

Vitamin C is an essential water-soluble antioxidant that humans cannot synthesize, requiring continuous dietary intake from fruits and vegetables.

Ascorbic acid is critical for:

  • Collagen synthesis (cofactor for prolyl & lysyl hydroxylases)
  • Immune system function
  • Carnitine synthesis
  • Neurotransmitter production (norepinephrine)
  • Iron absorption (reduces Fe³⁺ → Fe²⁺)
  • Antioxidant defense (neutralizes free radicals)

Deficiency leads to scurvy, a classic disease marked by connective tissue failure.

Physiological Role

1. Collagen Formation

Essential for hydroxylation reactions → stabilizes collagen triple helix.

2. Immune Function

  • Enhances neutrophil function
  • Supports lymphocyte proliferation
  • Reduces inflammation

3. Antioxidant Activity

Ascorbic acid and dehydroascorbate form a reversible redox pair.

4. Iron Metabolism

Improves non-heme iron absorption.

5. Hormone & Neurotransmitter Synthesis

Cofactor in norepinephrine and peptide hormone synthesis.

Clinical Significance

LOW VITAMIN C

SCURVY - classic deficiency syndrome.

Symptoms

  • Gingival bleeding, swollen gums
  • Petechiae, ecchymoses
  • Corkscrew hair
  • Poor wound healing
  • Fatigue, malaise
  • Arthralgia, myalgia
  • Anemia (due to ↓ iron absorption)
  • Depression / irritability

At-risk groups

  • Elderly
  • Alcoholics
  • Poor dietary intake
  • Smokers (higher requirement)
  • Malabsorption
  • Dialysis patients
  • Chronic illness
  • Infants fed boiled milk (historically)

HIGH VITAMIN C

Usually due to supplements.

Symptoms:

  • Diarrhea
  • Abdominal cramps
  • Oxalate kidney stones (rare)
  • False lab results in glucose testing (interference)

Food sources seldom cause toxicity.

Reference Intervals

(Tietz 8E + Mayo + ARUP + NIH)

Serum Vitamin C

  • 23 – 85 µmol/L
     (= 4 – 15 mg/L)
    (= 0.4 – 1.5 mg/dL)

Deficiency

  • < 11 µmol/L (classic scurvy risk)

Marginal status

  • 11 – 23 µmol/L

Diagnostic Uses

1. Diagnosis of Scurvy

Low levels in symptomatic patients.

2. Nutritional Assessment

In elderly, critically ill, or malnourished patients.

3. Monitoring Supplementation

For high-dose protocols or parenteral therapy.

4. Evaluation of Poor Wound Healing

Vitamin C deficiency delays collagen repair.

5. Assessment in Chronic Disease

Low levels seen in:

  • Sepsis
  • Inflammatory disorders
  • Burns
  • Chronic illness

Analytical Notes

  • Fasting blood sample required (levels fluctuate with meals).
  • Protect sample from light and air (ascorbate is unstable).
  • Centrifuge immediately and analyze or freeze plasma.
  • LC-MS/MS or HPLC preferred for accuracy.

Clinical Pearls

  • Smokers need ~35 mg/day more due to increased oxidative stress.
  • Vitamin C deficiency often coexists with folate deficiency in alcoholism.
  • High-dose IV vitamin C may interfere with:
    • Glucose meters (false highs)
    • Some creatinine assays
  • Early scurvy symptoms mimic rheumatologic disease or vasculitis.
  • Severe deficiency reverses rapidly with supplementation.

Interesting Fact

Sailors historically developed scurvy on long voyages until citrus fruit supplementation (lemons, limes) became standard - giving rise to the term “Limeys.”

References

  1. Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Vitamins
  2. NIH Office of Dietary Supplements - Vitamin C
  3. WHO Micronutrient Guidelines
  4. Mayo Clinic Laboratories - Ascorbic Acid Test
  5. ARUP Consult - Vitamin C
  6. MedlinePlus - Vitamin C Testing

Last updated: January 27, 2026

Reviewed by : Medical Review Board

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