Vitamin C: Beyond Basics, Liposomal and IV Forms

What Vitamin C Actually Does

The antioxidant framing is accurate but incomplete, and it obscures the roles that matter more.

Collagen synthesis. Prolyl hydroxylase and lysyl hydroxylase require vitamin C to hydroxylate proline and lysine residues in procollagen, which is what allows the triple helix to form and stabilise. Without it, collagen is structurally defective, which is the mechanism behind scurvy: bleeding gums, poor wound healing, connective tissue failure.

Other dioxygenases. Vitamin C is a cosubstrate for the same family of iron-dependent dioxygenases that alpha-ketoglutarate serves, including the TET enzymes that demethylate DNA and the hypoxia-inducible factor hydroxylases. This connects vitamin C status to epigenetic regulation, which is a considerably more interesting story than free radical scavenging.

Neurotransmitter and carnitine synthesis. Required for dopamine beta-hydroxylase, which converts dopamine to noradrenaline, and for carnitine synthesis, which supports fatty acid transport into mitochondria.

Iron absorption. Vitamin C reduces ferric to ferrous iron and substantially increases non-haem iron absorption, which is useful for anyone on a plant-based diet and a consideration for anyone with iron overload.

Antioxidant recycling. It regenerates vitamin E from its oxidised form, which is where the antioxidant network idea comes from.

The Saturation Problem

Vitamin C absorption depends on the SVCT1 transporter in the intestine, and transporters saturate.

Controlled pharmacokinetic work established the shape of the curve: fractional absorption is near complete at doses up to about 100 mg, falls to roughly half at 500 mg, and continues falling as doses rise. Plasma concentration plateaus at 70 to 90 micromolar and renal excretion increases sharply beyond that, so additional oral vitamin C ends up in urine rather than in tissue.

This means a 1,000 mg tablet does not deliver ten times what a 100 mg tablet does. It delivers modestly more, at a lower efficiency, with the surplus excreted. Dividing doses across the day raises the plateau slightly; it does not remove it.

Tissue concentrations are separately regulated. Leucocytes, adrenal glands, brain and eye maintain concentrations far above plasma through active transport, and they saturate at intakes well below what supplements typically provide.

Liposomal and Intravenous Routes

Liposomal vitamin C. Encapsulating vitamin C in phospholipid vesicles is intended to bypass the saturable transporter by allowing absorption through a different route. Comparative studies do show higher plasma concentrations from liposomal preparations than from equivalent oral doses, with the difference modest rather than transformative, and product quality varies enormously since genuine liposomal encapsulation is harder to achieve than to claim. Whether the higher plasma concentration produces better outcomes has not been tested, because the trials that measured absorption did not measure endpoints.

Intravenous vitamin C. This is a genuinely different pharmacology. Bypassing the gut entirely allows plasma concentrations in the millimolar range, more than a hundredfold above the oral ceiling. At those concentrations vitamin C behaves as a pro-oxidant in some tissues, generating hydrogen peroxide, which is the basis for its investigation in oncology contexts. Trials in sepsis have been prominent and their results have been mixed to negative, with large well-conducted trials finding no benefit and one finding potential harm. Intravenous vitamin C is a medical intervention, not a wellness one, and it should not be conflated with oral supplementation.

The Evidence for Common Uses

Common cold

The most examined and most misunderstood. Regular supplementation does not reduce the incidence of colds in the general population. It does modestly reduce duration, by roughly eight percent in adults across trials. In people under extreme physical stress, including marathon runners and soldiers in subarctic conditions, regular supplementation halved incidence in the trials conducted. Taking vitamin C after symptoms start has not shown consistent benefit.

Skin

Adequate vitamin C is required for collagen synthesis, so status matters. Topical vitamin C at appropriate concentration and pH has reasonable evidence for photoageing measures, and topical and oral routes are not interchangeable, since skin concentrations are hard to raise substantially through oral intake once saturated.

Iron absorption

Well established. Taking vitamin C with a plant-based iron source substantially increases absorption, which is genuinely useful for vegetarians and a consideration for anyone with haemochromatosis.

Exercise

Here the direction reverses. High-dose vitamin C, typically 1,000 mg with vitamin E, has been shown to blunt training adaptations including mitochondrial biogenesis markers and insulin sensitivity improvements. Anyone training seriously has a specific reason to keep high doses away from the training window.

Cardiovascular and mortality outcomes

Supplementation trials have been null. Observational associations between higher intake and better outcomes have not survived randomised testing, which is a familiar pattern for antioxidant nutrients.

Dose, Safety and Practical Notes

• 75 to 90 mg per day. Requirement in most guidance, with smokers requiring more due to increased turnover.
• 200 mg per day. Approximately the intake that saturates plasma and tissue in most people. This is the number that matters practically and it is far below typical supplement doses.
• 500 to 1,000 mg per day. Common supplemental range, mostly excreted, harmless in most people.
• 2,000 mg per day. Commonly cited upper level, above which osmotic diarrhoea becomes likely.

Safety considerations. Vitamin C is metabolised partly to oxalate, and high doses increase urinary oxalate, which matters for anyone with a history of calcium oxalate kidney stones. It increases iron absorption, which is undesirable in haemochromatosis. High doses interfere with several laboratory assays including some glucose meters and HbA1c methods. And people with G6PD enzyme variants should avoid very high doses, where haemolysis has been reported.

Food first is reasonable here. A kiwi, a bell pepper, a serving of broccoli or a citrus fruit each supply substantial vitamin C, and dietary sources bring the rest of the plant matrix with them. Given that plasma saturates around 200 mg, a diet including several vitamin C-rich foods daily leaves little for a supplement to add.