An essential nutrient the body cannot make. The surest gains are preventing deficiency, modestly shortening colds taken regularly, sharply cutting colds under extreme physical stress, and boosting plant-iron absorption. Claims of longer life, lower cancer risk, and brain protection rest on weaker evidence. Risks stay modest and tied to large doses. (Full Review)

Protocol

Maintenance Dose

200–500 mg/day

Range that fully saturates plasma and tissues in most people; higher yields diminishing returns

Split Dosing

250 mg twice daily

Splitting achieves higher, steadier levels than a single dose, particularly above ~500 mg/day

Timing

With meals

Reduces stomach upset; pairing with a plant-based meal maximizes iron absorption

Time to effect

Deficiency Signs

Days to weeks

Deficiency signs resolve after adequate intake begins

Tissue Saturation

1–2 weeks

Blood and tissue levels rise within days and saturate

Cold Benefit

Ongoing daily use

Appears only with continuous use, not from starting at symptom onset

Benefits

High: Prevention and reversal of deficiency and scurvy; reduced duration and severity of the common cold

Medium: Enhanced absorption of plant-based iron; modest reduction in blood pressure; reduced cold incidence under heavy physical stress

Low: Lower all-cause and cardiovascular mortality; support for skin collagen and wound healing; reduced cancer risk

Speculative: High-dose intravenous vitamin C as a cancer adjunct; cognitive protection and dementia risk reduction

Contraindications

Iron overload / hereditary hemochromatosis (gram-level doses)

G6PD deficiency (high intravenous doses)

Chronic kidney disease (eGFR <30) or dialysis (gram-level doses)

Recurrent calcium-oxalate stone formers (gram-level doses)

Key Interactions

Anticoagulants and antiplatelet drugs (warfarin, aspirin)

Iron-chelating therapy (deferoxamine)

Statins and niacin (atorvastatin, extended-release niacin)

Chemotherapy and radiation (cisplatin, carboplatin, cyclophosphamide)

Aluminum-containing antacids (aluminum hydroxide, sucralfate)

Over-the-counter analgesics (aspirin, ibuprofen)

Iron and copper supplements

Additive antioxidant supplements (vitamin E, alpha-lipoic acid, N-acetylcysteine)

Risk & Side Effects

High: Gastrointestinal distress at high oral doses

Medium: Increased kidney stone risk; iron overload from enhanced iron absorption

Low: Interference with laboratory and glucose-meter readings; hemolysis in G6PD deficiency with high intravenous doses

Speculative: Blunting of exercise training adaptations; increased cardiovascular risk in diabetic postmenopausal women

Monitoring

Marker	Target	Why
Plasma vitamin C (ascorbic acid)	50–70 µmol/L	Confirms adequacy and tissue saturation
Serum ferritin	50–150 ng/mL	Screens for iron deficiency or overload before high-dose use
Transferrin saturation	20–40%	Detects iron overload that vitamin C could worsen
24-hour urinary oxalate	<40 mg/24h	Gauges kidney-stone risk from vitamin C's oxalate load
eGFR (kidney function)	>60 mL/min/1.73m²	Identifies reduced filtering that concentrates oxalate and aluminum risk
Fasting glucose / HbA1c	Glucose 70–90 mg/dL; HbA1c <5.4%	Tracks metabolic health where blood-pressure and diabetes effects are relevant

Cadence: Recheck status and flagged markers ~8–12 weeks after a meaningful change in intake, then every 6–12 months; annual urinary oxalate for stone-formers or high-dose users

Qualitative Assessment

Frequency, duration, and severity of colds over a season
Energy and freedom from unexplained fatigue
Gum health and absence of easy bruising or slow-healing wounds
Skin quality and connective-tissue resilience
Exercise recovery and tolerance of heavy training

Vitamin C for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment