An Essential, Antioxidant Vitamin
Vitamin C, or ascorbic acid, is a water-soluble vitamin essential to the human body. It is a major antioxidant and a cofactor for numerous enzymatic reactions.
It has been linked for centuries to the prevention of scurvy. Its history illustrates, in exemplary fashion, the path of medicine: from the empirical observation of a deficiency disease to the identification, isolation, and industrial synthesis of a precise molecule.
From Scurvy to the Discovery of the Molecule
The history of ascorbic acid is inseparable from that of scurvy, a deficiency disease that decimated the crews of major maritime expeditions. In 1747, Scottish physician James Lind conducted one of the first controlled clinical trials in history aboard HMS Salisbury: he demonstrated that citrus fruits cured scurvy. His findings, published in 1753, eventually led — belatedly — to the distribution of lemon juice in the Royal Navy.
It would take until the 20th century to identify the molecule responsible. In 1907, Norwegian researchers Axel Holst and Theodor Frølich developed an animal model of scurvy in guinea pigs, an animal that, like humans, cannot synthesize vitamin C. Between 1928 and 1932, Hungarian biochemist Albert Szent-Györgyi isolated a substance he initially named "hexuronic acid" — first from adrenal glands, then from paprika — while Charles Glen King, in the United States, established that it was the antiscorbutic factor.
Determining the Structure and Industrial Synthesis
In 1933, British chemist Walter Norman Haworth determined the molecule's structure and proposed the name ascorbic acid, literally "anti-scurvy." That same year, Tadeus Reichstein developed an industrial synthesis route — the Reichstein process — which would make vitamin C accessible on a large scale and at low cost.
This body of work was recognized with two Nobel Prizes in 1937: the Prize in Medicine for Szent-Györgyi and the Prize in Chemistry for Haworth.
The Biological Role of Vitamin C
Ascorbic acid is an essential enzymatic cofactor, particularly for the hydroxylases involved in collagen synthesis (hydroxylation of proline and lysine). This explains the manifestations of scurvy: fragile blood vessels, hemorrhages, poor wound healing, and loosening of the teeth.
It is also a powerful antioxidant, able to trap free radicals and regenerate other antioxidants such as vitamin E. It is also involved in iron absorption and in the metabolism of several neurotransmitters.
Notably, humans are among the rare mammals unable to synthesize vitamin C, due to the lack of a functional enzyme, L-gulonolactone oxidase. Dietary or medicinal intake is therefore strictly essential.
As an Active Ingredient: Treating and Preventing Deficiency
It is used to prevent and treat vitamin C deficiency (scurvy), as a supplement during states of fatigue or convalescence, and in numerous over-the-counter products.
Its preferred dosage forms are effervescent tablets, chewable tablets, and oral solutions, owing to its excellent solubility and tangy taste.
As an Excipient: Antioxidant and Acidifying Agent
It serves as an antioxidant to protect other active ingredients that are sensitive to oxidation, and as an acidifying agent in effervescent formulations, where it reacts with bicarbonates to release the carbon dioxide responsible for effervescence.
Formulation Constraints
Its main challenge is its sensitivity to humidity, light, heat, and oxygen, which requires protective packaging (blister packs, desiccants) and, in some cases, coated or buffered forms to preserve its stability over time.