1Pharmacokinetics of Ascorbic Acid
Vitamin C (L-ascorbic acid) is a water-soluble six-carbon lactone that humans cannot synthesise de novo due to the absence of the enzyme L-gulonolactone oxidase. This makes dietary or supplemental intake mandatory. At physiological doses (up to 200 mg/day), intestinal absorption approaches 70–90% via sodium-dependent vitamin C transporters (SVCT1 and SVCT2) in the duodenum and jejunum. This is where a key clinical principle emerges: absorption is saturable and dose-dependent.
At oral doses above 1000 mg, bioavailability drops below 50%, with surplus excreted unchanged in urine. This plateau limits the utility of very high oral doses in clinical practice. In states of severe oxidative stress — sepsis, major burns, post-cardiac surgery — tissue Vitamin C levels plummet, and only parenteral (IV) administration can reliably replete plasma and tissue concentrations to pharmacological levels.
| Parameter | Value | Clinical Significance |
|---|---|---|
| Plasma half-life | ~10–20 days (physiological) | Deficiency develops in 4–6 weeks of zero intake |
| Plasma saturation | ~70 µmol/L at 200 mg/day oral | Higher oral doses do not raise plasma levels proportionally |
| Oral bioavailability at 1000 mg | ~50% | Divided doses improve total absorption |
| IV bioavailability | ~100% | Required for pharmacological (>1 mmol/L) plasma levels |
| Primary metabolism | Oxalate (via 2-keto-gulonate) | Urinary oxalate rises significantly above 1000 mg/day |
| Protein binding | Negligible | Freely distributed; crosses placenta |
2Scurvy — Indian Clinical Picture and Treatment Protocols
Scurvy is caused by chronic Vitamin C deficiency, defined as plasma ascorbate below 11 µmol/L. Despite being considered a historical disease, scurvy remains clinically relevant in India among the elderly living alone, chronic alcoholics, patients with tea-and-toast diets, children with autism-related food aversions, and patients on prolonged TPN without Vitamin C supplementation.
Pathophysiology
The biochemical basis of scurvy is the failure of prolyl hydroxylase and lysyl hydroxylase — both Vitamin C-dependent enzymes — to hydroxylate procollagen. Without these hydroxylations, collagen triple helices cannot form stable cross-links, producing structurally weak connective tissue throughout the body. This manifests as vascular fragility (perifollicular haemorrhage), impaired wound healing, and osteoporosis.
Clinical Recognition
The hallmarks of scurvy progress in a predictable sequence. Early: follicular hyperkeratosis and "corkscrew hairs" around hair follicles on the thighs and buttocks. Intermediate: perifollicular haemorrhage and "woody oedema" of the lower limbs. Advanced: scorbutic gingivitis (friable, purple-blue gums bleeding with minimal provocation), subperiosteal haemorrhage causing bone pain, and large ecchymoses. In children, the classic "frog-leg" posture from painful lower-limb haemorrhages is pathognomonic.
Standard Replacement Protocol
| Population | Dose | Route | Duration | Notes |
|---|---|---|---|---|
| Confirmed Scurvy — Adult | 500–1000 mg/day | Oral (divided doses) | ≥1 month | 500 mg BD or 250 mg QDS |
| Severe/Hospitalised Adult | 1000 mg/day | IV or Oral | Until symptoms resolve | IV if GI absorption impaired |
| Paediatric Scurvy | 100–300 mg/day | Oral (divided doses) | 2–4 weeks | Weight-based: ~10 mg/kg/day; max 300 mg |
| Subclinical / At-Risk Adult | 250–500 mg/day | Oral | Ongoing until diet improved | Elderly, alcoholics, institutional patients |
| Prophylaxis (smokers) | +35 mg/day above RDA | Oral | Ongoing | ICMR: smokers need 110–125 mg/day minimum |
3Vitamin C in Wound Healing, Burns, and Surgical Recovery
Ascorbic acid is the non-negotiable co-factor for both prolyl hydroxylase and lysyl hydroxylase, the enzymes that introduce stability-conferring hydroxyl groups into procollagen chains. Without these modifications, collagen cannot form the triple-helical structure required for tensile strength. In any healing wound, Vitamin C is being consumed rapidly at the site — local tissue levels often become depleted even when systemic plasma levels appear normal.
Burns — A Special High-Demand Scenario
Thermal injury creates massive oxidative stress and dramatically increases metabolic demand for Vitamin C — requirements can reach 10–20 times the RDA. Large burns cause a capillary leak syndrome in which Vitamin C, as an antioxidant, helps protect vascular endothelial integrity and may reduce resuscitation fluid volumes when given as high-dose IV within the first 24 hours.
| Scenario | Dose | Route | Duration | Notes |
|---|---|---|---|---|
| Post-operative wound healing | 500 mg daily | Oral | Until wound closed | Elective surgery — pre-load if malnourished |
| Major surgery / large wounds | 1000–2000 mg daily | Oral | Until secondary closure | Divided into BD–TDS doses |
| Minor-to-moderate burns (<20% BSA) | 1000–2000 mg daily | Oral or IV | 7–14 days | Maintain until re-epithelialisation |
| Major burns (≥20% BSA) | 66 mg/kg/hour × 24h | IV infusion | First 24 hours only | Niwa protocol; monitor urine output hourly |
| Chronic non-healing wounds | 500–1000 mg daily | Oral | 4–8 weeks; reassess | Check serum Vit C — subclinical deficiency common |
4Synergistic Role in Iron Deficiency Anaemia
Iron deficiency anaemia is the single most common micronutrient deficiency in India, affecting an estimated 50–60% of women of reproductive age. Vitamin C is one of the most potent enhancers of non-haem iron absorption known. Its mechanism is dual: it reduces ferric iron (Fe³⁺) to ferrous iron (Fe²⁺), which is the only form transported across intestinal epithelium by DMT-1, and prevents insoluble precipitate formation with dietary phytates and tannins.
| Elemental Iron Dose | Vitamin C Co-dose | Timing | Notes |
|---|---|---|---|
| 30–60 mg elemental iron | 200 mg | Same dose; fasting or mid-meal | Standard paediatric iron co-therapy |
| 60–100 mg elemental iron | 200–500 mg | Simultaneously; avoid tea/milk ±1h | Adult iron deficiency anaemia |
| 100–200 mg elemental iron | 500 mg | Simultaneously; empty stomach preferred | Severe anaemia; post-partum |
| IV iron (any dose) | Not required | — | Bypasses GI absorption — Vit C has no role |
5High-Dose IV Vitamin C — Sepsis and Oncology Protocols
Intravenous Vitamin C (IVC) achieves pharmacological plasma levels of 10–20 mmol/L — concentrations 100–200 times higher than oral saturation, exerting pro-oxidant, anti-inflammatory, and immunomodulatory effects.
| Protocol | Dose | Route | Duration | Notes |
|---|---|---|---|---|
| CITRIS-ALI (Sepsis/ARDS) | 1.5 g q6h (6 g/day) | IV infusion over 30–60 min | 4 days | Dilute in 100 mL NS; G6PD screen mandatory |
| Marik Protocol adjunct | 1.5 g q6h | IV | 4 days or ICU discharge | Add thiamine 200 mg BD + hydrocortisone |
| Burns — Niwa Protocol | 66 mg/kg/hour | Continuous IV | First 24 hours only | Reduces resuscitation fluid; monitor UO hourly |
| Palliative / Oncology IVC | 15–100 g | Slow IV over 60–90 min | 2–3×/week; variable | G6PD screen mandatory; renal monitoring |
6Toxicity, Contraindications, and Renal Safety
Approximately 40% of urinary oxalate is derived from ascorbate catabolism. At doses above 1000 mg/day, urinary oxalate excretion increases significantly and in susceptible individuals can precipitate calcium-oxalate urolithiasis. Patients with CKD, a history of oxalate stones, or hyperoxaluria should not receive chronic high-dose oral Vitamin C without specialist guidance.
| Risk / Interaction | Threshold / Context | Management |
|---|---|---|
| Calcium-oxalate nephrolithiasis | >1000 mg/day chronic oral | Limit to ≤500 mg/day in stone history; high fluid intake |
| G6PD haemolysis (IV) | >15 g/dose IV | Mandatory G6PD screen before high-dose IV protocol |
| Urine glucose (dipstick) — false negative | Any high dose | Use glucose oxidase method; warn diabetic patients |
| Occult blood (faecal) — false negative | Any high dose | Discontinue 3 days before faecal OBT testing |
| Iron overload (haemochromatosis) | Any supplemental dose | Avoid supplemental Vitamin C — enhances absorption further |
7Vitamin C in Pregnancy and Lactation
Vitamin C requirements increase modestly in pregnancy and lactation. The ICMR (2020) recommends 80 mg/day in pregnancy and 85 mg/day in lactation, well above the non-pregnant adult RDA of 65–75 mg/day. Supplemental Vitamin C is safe at nutritional doses; however, doses above 2000 mg/day are avoided due to theoretical concerns of neonatal rebound scurvy.