What is vitamin C made of? The Chemical Composition and Nutritional Role of Ascorbic Acid

October 29, 2025 •

4 min read

Unlike most other mammals, humans and primates cannot produce their own vitamin C and must obtain it from their diet. But what is vitamin C made of on a chemical level, and how does its molecular structure influence its essential role in human health?

Quick Summary

Vitamin C, also known as L-ascorbic acid ($C_6H_8O_6$), is an essential, water-soluble organic compound derived from glucose. It is sourced through diet and industrial production due to the human inability to synthesize it.

Key Points

Chemical Formula ($C_6H_8O_6$): Vitamin C, or L-ascorbic acid, is an organic compound with six carbon, eight hydrogen, and six oxygen atoms.
Glucose Derivation: The molecular structure of vitamin C is a lactone derived from glucose, a simple sugar.
Essential Nutrient: Humans cannot synthesize their own vitamin C due to a genetic mutation and must get it from their diet.
Potent Antioxidant: The chemical structure's ene-diol group allows vitamin C to act as an effective antioxidant by donating electrons to neutralize free radicals.
Forms of the Vitamin: Vitamin C exists in both a reduced form (ascorbic acid) and an oxidized form (dehydroascorbic acid), which are both biologically active.
Primary Dietary Sources: The richest sources of vitamin C are fresh fruits and vegetables, including citrus fruits, peppers, and broccoli.
Sensitive to Degradation: Vitamin C is highly sensitive to environmental factors like heat and light, which can reduce its nutritional content in food.
Industrial Production: Synthetic vitamin C, found in most supplements, is produced industrially from glucose and is chemically identical to the natural form.

The Chemical Composition of Ascorbic Acid

Vitamin C's scientific name is L-ascorbic acid, and its chemical formula is $C_6H_8O_6$. This formula indicates that each molecule contains six carbon, eight hydrogen, and six oxygen atoms. Structurally, it is a six-carbon lactone and is classified as a weak sugar acid because it is derived from glucose. The biologically active form is the L-enantiomer, which exists naturally in foods. Its structure contains an ene-diol group, which consists of two hydroxyl (-OH) groups attached to adjacent carbon atoms joined by a double bond. This specific configuration is what gives ascorbic acid its potent antioxidant properties, allowing it to readily donate electrons to neutralize harmful free radicals.

Molecular Structure Details

L-ascorbic acid's five-membered lactone ring and its ene-diol group make it a strong reducing agent. When it donates an electron, it forms a stabilized radical known as the ascorbyl radical, which is relatively unreactive and does not cause cellular damage. This makes it a primary defense against oxidative stress in the body. When it donates a second electron, it becomes dehydroascorbic acid (DHA), which can be recycled back into ascorbic acid within cells. The presence of these two forms, in a reversible oxidation-reduction system, is fundamental to how vitamin C functions physiologically. The acidity of ascorbic acid is also a result of its unique chemical structure.

The Genetic Reason Humans Need Dietary Vitamin C

The inability of humans to synthesize vitamin C is due to a genetic mutation that occurred millions of years ago. Most animals can synthesize their own ascorbic acid from glucose in their liver or kidneys. However, humans and a few other species, such as primates and guinea pigs, lack the functional gene that codes for L-gulonolactone oxidase, the final enzyme in the biosynthesis pathway. This loss of function means that a consistent dietary intake of vitamin C is absolutely essential to prevent deficiency and its associated disease, scurvy. This highlights why vitamin C is classified as a vitamin; it is a vital nutrient that the body cannot produce on its own.

Natural and Industrial Sources of Ascorbic Acid

For humans, the primary source of vitamin C is through a healthy diet rich in fruits and vegetables. Beyond natural food sources, a large portion of the vitamin C in supplements and fortified foods comes from industrial production. The modern process, largely developed in China, uses a two-step fermentation process starting with D-glucose (a monosaccharide). This method is more efficient than the older Reichstein process and allows for the mass production of synthetic ascorbic acid. Notably, synthetic and natural vitamin C are chemically identical and exhibit the same biological activity.

Food Sources Rich in Vitamin C

Citrus Fruits: Oranges, lemons, grapefruit, and their juices.
Berries: Strawberries, blackcurrants, and raspberries.
Peppers: Especially red and green bell peppers.
Cruciferous Vegetables: Broccoli, brussels sprouts, cauliflower, and cabbage.
Tropical Fruits: Kiwi fruit, mango, and papaya.
Potatoes: A common source, especially white potatoes.

The Nutritional Functions of Ascorbic Acid

Vitamin C's role in the body is extensive and critical for overall health. Its primary functions are related to its antioxidant and coenzyme activities. As an antioxidant, it neutralizes free radicals that can cause cellular damage, which contributes to the aging process and chronic diseases. As a coenzyme, it is vital for several enzymatic processes. For example, it helps synthesize collagen, a key protein for maintaining healthy skin, cartilage, bones, and blood vessels. It is also essential for wound healing, as it aids in forming scar tissue. Additionally, vitamin C improves the absorption of non-heme iron, the type found in plant-based foods.

Understanding Vitamin C Supplementation

When it comes to supplements, several forms of vitamin C are available. The most common is ascorbic acid, which has excellent bioavailability. Other forms, like sodium ascorbate (a buffered form), are less acidic and may be preferred by those with gastrointestinal sensitivity. Research has generally found that different supplemental forms have similar bioavailability, although minor differences in plasma or tissue concentrations have been observed in some studies. Choosing a supplement depends on individual needs and tolerance.

Factors Affecting Vitamin C Stability

Vitamin C is sensitive to various environmental factors, which affects its content in foods and supplements. It is water-soluble and can be easily destroyed by heat, light, and oxygen.

Comparison of Natural and Synthetic Vitamin C


Feature	Natural Vitamin C (from food)	Synthetic Vitamin C (supplements)
Source	Fruits, vegetables	Industrially produced from glucose
Chemical Identity	L-ascorbic acid and its oxidized form, dehydroascorbic acid	Chemically identical L-ascorbic acid
Bioavailability	High; absorbed well alongside other nutrients and bioflavonoids	High; similar to food-based ascorbic acid
Stability	Easily degraded by heat, light, and prolonged storage	Varies by formulation; crystalline powder is more stable when dry
Associated Compounds	Comes with a complex mix of phytonutrients and minerals	Can be formulated with other minerals (e.g., calcium ascorbate) or bioflavonoids
Overall Effect	Offers a holistic nutritional benefit from a wide range of compounds	Provides a targeted and concentrated dose of vitamin C

Conclusion

In summary, what is vitamin C made of is a six-carbon molecule called L-ascorbic acid ($C_6H_8O_6$), a derivative of glucose. Its unique chemical structure, featuring an ene-diol group, is responsible for its powerful antioxidant abilities. Due to a genetic deficiency, humans cannot synthesize this vital nutrient and must rely on dietary intake from natural food sources like fruits and vegetables, or through industrially produced supplements. The body's efficient use of both reduced and oxidized forms of vitamin C underscores its importance in numerous physiological processes, from collagen formation and immune function to iron absorption. Being mindful of its sensitivity to heat and light is key to preserving its nutritional value in the foods we eat.

For more in-depth information, the National Institutes of Health provides a comprehensive fact sheet on vitamin C.

Frequently Asked Questions

Yes, L-ascorbic acid is the chemically active form that is commonly known as vitamin C. In nutritional literature, the terms are often used interchangeably to refer to the biologically active molecule.

Humans lack the functional enzyme L-gulonolactone oxidase, which is necessary for the final step of vitamin C synthesis. This is due to a non-functional gene that resulted from a mutation long ago.

No, synthetic and naturally derived ascorbic acid are chemically identical. Studies have shown they have equivalent bioavailability and biological activity.

Cooking can significantly reduce vitamin C content because it is water-soluble and heat-sensitive. Higher temperatures, longer cooking times, and using more water all increase the loss of the vitamin.

In laboratory settings and in the presence of high doses of free transition metals (like iron or copper), vitamin C can exhibit pro-oxidant effects. However, this is generally not a concern under normal physiological conditions in the body.

Dehydroascorbic acid (DHA) is the oxidized form of vitamin C. It is also biologically active and can be converted back into ascorbic acid inside the cells, which is a key part of the body's vitamin C recycling process.

Severe vitamin C deficiency leads to scurvy. Symptoms can include fatigue, bleeding gums, easy bruising, poor wound healing, and weakened connective tissues.