Vitamin C
vitamin
ApprovedGeneral information about nutrients. No diagnosis, no medical advice. If you take medication, are pregnant or have a medical condition, talk to your doctor before taking supplements.
Overview
Water-soluble vitamin. Vitamin C contributes to the normal function of the immune system. Vitamin C increases iron absorption.
Interactions
Vitamin C reduces Fe³⁺ to Fe²⁺ in the gastric lumen and forms a soluble chelate that remains bioavailable at the alkaline pH of the duodenum, increasing non-heme iron absorption 2-6 fold.
Vitamin C reduces chromium(VI) to chromium(III) in the acidic stomach environment, enhancing its bioavailability and reducing potential toxicity of higher oxidation states.
Vitamin C maintains selenium in its reduced, biologically active forms and enhances intestinal absorption of selenite by reducing it to elemental selenium for transport.
Research status
Vitamin C contributes to the regeneration of the reduced form of vitamin E. Vitamin C contributes to normal collagen formation for the normal function of skin.
Top 5 food sources
Expert opinions
Bryan Johnson Blueprint
Johnson keeps supplemental vitamin C modest at 500 mg daily in the Blueprint stack, relying primarily on whole-food sources like broccoli, kiwi, and citrus. He avoids megadosing because oral absorption plateaus at roughly 200 mg per dose and renal clearance removes the excess. The dose is timed with breakfast alongside other water-soluble nutrients for steady plasma saturation. Tracked biomarkers include hsCRP and antioxidant-capacity panels rather than plasma vitamin C itself.
Recommended dose: ~250 mg
Source: Blueprint Protocol
Current Research
Oral absorption saturates around 200 mg per dose, with bioavailability dropping from about 98 % at 200 mg to under 50 % at 1,250 mg. Liposomal and sustained-release formulations improve plasma AUC but have not proven clinically superior for non-deficient adults.
Source: Current Research
NIH
The NIH UL of 2,000 mg/day for vitamin C is a tolerance-based limit — above this dose, osmotic diarrhea, cramping, and nausea become common because absorption becomes saturated and unabsorbed ascorbate draws water into the gut. Saturable SVCT1/SVCT2 transporters limit oral bioavailability to ~70% at 200 mg, falling below 50% by 1 g and <20% beyond 2 g. The NIH also notes that high doses may increase oxalate formation and therefore kidney-stone risk in susceptible individuals. RDA is 90 mg for men, 75 mg for women, plus 35 mg for smokers due to higher oxidative turnover. No UL from iron-overload interactions in healthy people, but caution in hemochromatosis.
Recommended dose: 75–90 mg
Source: NIH
Dr. Strunz
Strunz recommends 1 to 5 g vitamin C daily split across meals, far beyond the 100 mg RDA, based on his orthomolecular approach. Vitamin C contributes to the protection of cells from oxidative stress. Vitamin C contributes to the regeneration of the reduced form of vitamin E. He prefers liposomal or buffered ascorbate for higher plasma peaks and better GI tolerance. According to Strunz, smokers and athletes need the upper range.
Recommended dose: 1–3 g
Source: Dr. Strunz
Expert profiles summarise publicly available statements. The named people do not cooperate with Stackwell and have not authorised these summaries. Not medical advice.
Large disagreement on optimal dose. Absorption plateaus around 200mg per dose.