Calculate vitamin C dose by goal — RDA, immune support, iron co-factor, or bowel-tolerance protocol. Most absorption saturates around 200 mg per dose, so 1g+ single doses waste most of what you take. Split dosing matters. Math, not medical advice.
Your goal
200 mg/day
Target daily dose (split as shown for best absorption)
Vitamin C forms compared
| Form | Cost | Best for | Trade-offs |
|---|---|---|---|
| Ascorbic acid | $ (cheap) | Default; well-studied | Acidic — heartburn for sensitive stomachs |
| Buffered (Ca/Na/Mg ascorbate) | $$ | Sensitive stomach; mineral co-supply | Calcium ascorbate adds calcium load — watch totals |
| Ester-C | $$$ | Marketed as longer-lasting in tissues | Patented blend; modest evidence vs cheap ascorbic acid |
| Liposomal | $$$$ | Higher peak plasma levels; chemo adjunct | 4-10× cost; clinical-endpoint advantage less proven for general use |
| Acerola / camu camu | $$$ | Whole-food concentrate with bioflavonoids | Lower mg per serving; pricey per mg |
| IV vitamin C | $$$$$ | Cancer adjunct (research); bypasses GI saturation | Rx only; allergic reaction risk; G6PD contraindication |
Why dose schedule matters more than total mg
- 200 mg single dose: ~70% absorbed (~140 mg)
- 500 mg single dose: ~50% absorbed (~250 mg)
- 1,000 mg single dose: ~33% absorbed (~330 mg)
- 2,000 mg single dose: ~20% absorbed (~400 mg)
- 5,000 mg single dose: ~10% absorbed (~500 mg)
- BUT: 200 mg × 5 throughout the day = 1,000 mg total at ~70% absorption each = ~700 mg absorbed.
So 1g/day split into 5 × 200 mg absorbs almost 2× better than 1g once. This is why “linus pauling style” mega-dose protocols ALWAYS split into hourly small doses.
Bowel-tolerance mega-dose protocol (Cathcart)
For acute illness, Robert Cathcart’s protocol uses vitamin C up to “bowel tolerance” — the dose just below what causes loose stools. Modern medicine views this approach skeptically, but the math is:
- Start: 1g every 1-2 hours awake.
- Increase until you experience loose stool / gas / cramping.
- Pull back to 75-80% of that dose.
- Maintain through illness; taper as you recover.
- Acute viral illness can tolerate 5-50g+ per day in some protocols vs 5-10g baseline tolerance for healthy adults.
- WARNING: not endorsed by major medical bodies. Risks: oxalate kidney stones (especially with kidney disease), iron overload (in hemochromatosis), G6PD hemolysis. Don’t do this without monitoring if you have ANY chronic condition.
Pairing with iron supplements
- Vitamin C + non-heme iron = 2-3× absorption boost per Cook 1973 and confirmed in many trials.
- 200-500 mg vitamin C with iron supplement or iron-rich meal is the standard pairing.
- Especially valuable for: vegetarians, women with heavy menstruation, athletes, anyone with iron deficiency.
- Take separately from coffee, tea, dairy (which block iron absorption) by 2 hours.
- See our iron dose calculator for form-specific guidance.
Safety considerations
- Upper Limit (UL): 2,000 mg/day for adults. Doses above mostly waste through urine but increase oxalate stone risk over time.
- Kidney stones: high-dose vitamin C is metabolized to oxalate. Risk is real for stone formers; controversial for general population.
- Iron overload: people with hereditary hemochromatosis should NOT mega-dose vitamin C (drives iron absorption above safe).
- G6PD deficiency: high-dose IV vitamin C can cause hemolytic anemia. Test before IV protocols.
- Stops taking it suddenly after chronic mega-dose: may cause rebound scurvy as body has down-regulated transporters. Taper over 1-2 weeks.
- Lab interference: high-dose vitamin C can falsely lower blood glucose readings on some meters; false-positive hemoglobin in stool tests.