An essential molecule with diverse functions
Vitamin C , chemically known as L-ascorbic acid , is one of the best-known water-soluble vitamins. It acts as a reducing agent , donating electrons and thus enabling numerous biochemical processes in the human body.
Unlike many animal species, humans cannot synthesize vitamin C themselves —they lack the enzyme L-gulonolactone oxidase , which catalyzes the final step of ascorbic acid biosynthesis. Therefore, vitamin C is essential and must be obtained through the diet.
Since its discovery in the 1930s, vitamin C has been intensively researched. Today, it is considered not only an antioxidant, but also a cofactor for enzymes , a regulator of redox balance , and a key metabolic partner in numerous physiological processes.
Vitamin C as an antioxidant – protection at the molecular level
Vitamin C is one of the most effective antioxidants in the body's aqueous environment. As an electron donor, it neutralizes reactive oxygen species (ROS) such as superoxide radicals, hydroxyl radicals, and hydrogen peroxide. It thereby prevents oxidative damage to lipids, proteins, and DNA .
mechanism
Its effect is based on its ability to donate electrons and subsequently transform into the radical intermediate form "semidehydroascorbate." This unstable compound is either reduced back to ascorbate or further oxidized to dehydroascorbate .
This reversible cycle enables continuous protection against oxidative stress .
Antioxidant network
Vitamin C acts in the body’s antioxidant network together with:
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Vitamin E , whose oxidized form (tocopheroxyl radical) can be regenerated by ascorbate,
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Glutathione (GSH) , which in its reduced form converts to ascorbate,
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and urate , which performs similar redox-active functions.
This interaction makes it clear that vitamin C does not act in isolation , but systemically – as part of a finely tuned redox biological network.
Research perspective
Studies (e.g., Frontiers in Physiology , 2022) show that the body's antioxidant capacity strongly depends on vitamin C status. High ascorbate levels are particularly observed in tissues with high metabolic turnover—such as leukocytes, adrenal glands, and brain —indicating its regulatory role in cellular homeostasis.
Cofactor in enzymatic reactions
In addition to its antioxidant effect, vitamin C is an essential cofactor for a variety of enzymes that catalyze redox reactions. Its function is to reduce metal ions (e.g., Fe³⁺, Cu²⁺) in the active sites of the enzymes to maintain catalytic activity.
Examples of enzymatic functions
| enzyme | process | Vitamin C function |
|---|---|---|
| Prolyl and lysyl hydroxylase | Collagen hydroxylation | Reduction of Fe³⁺ to Fe²⁺, stabilization of the triple helix structure |
| Dopamine β-hydroxylase | Synthesis of noradrenaline | Electron donor for Cu²⁺-dependent reaction |
| 4-Hydroxyphenylpyruvate dioxygenase | Tyrosine metabolism | Maintenance of enzyme activity via redox cycle |
| Carnitine synthase complexes | Fatty acid transport in mitochondria | Cofactor in the hydroxylation of trimethyllysine |
These reactions illustrate the biochemical versatility of vitamin C: it does not act primarily as an antioxidant, but as an electronic mediator in central metabolic pathways.
Research
Enzymatic dependence on vitamin C has been demonstrated in various tissues. In collagen synthesis, for example, a deficiency in ascorbate leads to unstable collagen fibers because hydroxylation reactions are incomplete.
Such mechanisms explain historical observations of scurvy – purely at the molecular level, without medical evaluation.
Vitamin C in energy metabolism and immune system
Energy generation
Vitamin C is involved in carnitine synthesis —a molecule necessary for the transport of long-chain fatty acids into the mitochondria . There, the fatty acids are oxidized to generate ATP . Without sufficient ascorbate, this transport pathway can be limited because the hydroxylation steps of carnitine-forming enzymes fail.
Immune function – scientifically speaking
Ascorbate is stored in high concentrations in leukocytes (white blood cells) . During inflammatory processes, oxidative stress develops there, which vitamin C buffers through electron donations.
It supports the integrity of cell membranes and the repair of oxidized molecules . Nutritional physiology studies show that vitamin C supports the function of neutrophils and macrophages —without any therapeutic implications.
This shows that vitamin C is not “stimulating” but rather regulating – a component of biochemical homeostasis processes in the immune system.
Vitamin C and iron – a biochemical partnership
One of the best known biochemical interactions is that between vitamin C and iron .
Vitamin C reduces trivalent iron (Fe³⁺) to divalent iron (Fe²⁺) , which is more easily absorbed in the small intestine. This reaction particularly improves non-heme iron absorption from plant sources.
At the molecular level, ascorbate forms soluble chelate complexes with iron, which promote absorption via DMT1 transporters in the enterocyte.
Studies in the American Journal of Clinical Nutrition confirm this mechanism and point to the contribution of vitamin C to blood formation and energy metabolism – an example of how redox chemistry and nutrition are directly linked.
Absorption, transport and storage in the body
Absorption
Vitamin C is actively absorbed via SVCT1 transporters (sodium-dependent vitamin C transporter 1) in the small intestine . These mechanisms are saturable —at higher doses, absorption does not increase linearly because the transport capacity is limited.
distribution
The highest concentrations are found in:
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Adrenal glands (stress hormone production),
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Liver (metabolism and detoxification),
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Brain (neurotransmitter regulation),
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Leukocytes (immune defense).
This shows that vitamin C accumulates preferentially in tissues with high metabolic activity.
regulation
Excesses are excreted via the kidneys . This homeostatic regulation maintains plasma levels within a physiologically constant range. Bioavailability studies indicate individual differences depending on transporter polymorphism and diet.
Buffered vitamin C – a formulation with a focus on tolerability
Chemically, buffered vitamin C does not differ in its biological activity, but rather in its pH value and chemical form .
During buffering, ascorbic acid is neutralized with minerals such as calcium, magnesium or sodium – so-called ascorbates are formed.
Chemical properties
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Ascorbic acid: pH 2–3, acidic
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Ascorbate: pH 6–7, neutral to slightly alkaline
The more neutral pH value may be milder for people with sensitive stomach lining.
In addition, ascorbates are more stable against oxidation because they are less reactive to environmental influences. In modern formulations, this chemical buffering serves to improve tolerability and shelf life – without altering the active ingredient itself.
Research perspectives and current developments
Vitamin C research has developed strongly towards systems biology in recent years.
The focus is no longer on pure antioxidant capacity, but rather on the role of vitamin C as a regulator of redox signaling pathways in cells.
Current focuses
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Epigenetics: Vitamin C influences dioxygenases involved in DNA and histone demethylation – relevant for cell programming and differentiation.
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Mitochondrial function: Studies show relationships between ascorbate status and oxidative phosphorylation .
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Plant substance combinations: New approaches explore synergies of vitamin C with polyphenols or flavonoids in order to modulate redox processes more specifically.
Future perspective
Research increasingly emphasizes the individual metabolic context – how genetic, nutritional and microbial factors influence the effectiveness of micronutrients.
Vitamin C remains a model molecule for understanding the interaction of nutrition, cell metabolism and redox biology.
Conclusion – a molecule of central importance
Vitamin C is far more than a classic antioxidant. It is a cofactor, redox regulator, and metabolic engine all in one—a molecule that acts at the interfaces of energy production, tissue regeneration, and cellular communication .
Research shows that ascorbate acts as a key biochemical factor in a wide variety of systems – from collagen synthesis to iron absorption, from the immune system to mitochondrial energy production.
Scientifically speaking, vitamin C is not a “simple vitamin” but a dynamic redox system that maintains the balance of biological processes – precise, versatile and indispensable.
