Vitamin C

Food sources

The richest food sources of Vitamin C are citrus fruits (oranges, lemons, grapefruit), kiwifruit, strawberries, red and yellow peppers – which contain concentrations up to three times higher than oranges – broccoli, Brussels sprouts, fresh parsley, and sea buckthorn berries, among the most concentrated plant sources of it. Cooking and exposure to air significantly degrade Vitamin C: up to 50–90% of the content can be lost through prolonged cooking or improper food storage.

Mechanism of action and main functions

Vitamin C acts through two main mechanisms:

• Enzyme Cofactor – Vitamin C is essential for the activity of numerous enzymes. The best known role is as a cofactor of prolyl and lysyl hydroxylases, the enzymes that modify procollagen during its synthesis. Without an adequate supply of Vitamin C, the Collagen produced is structurally unstable and cannot properly form the three-dimensional fibers that provide strength and integrity to skin, blood vessels, bone, and cartilage. This is the mechanism behind scurvy-the disease of severe Vitamin C deficiency.
• Water-soluble Anti oxidant – Vitamin C is the major water-soluble antioxidant in plasma and tissues. It neutralizes free radicals in the aqueous compartment, protecting lipids, proteins and DNA from oxidative stress. It cooperates with Glutathione-the main endogenous antioxidant-and with Vitamin E in the antioxidant chain: Vitamin C regenerates the reduced (active) form of Vitamin E after its oxidation.

Among other documented functions:

• Immune system support – Vitamin C accumulates in high concentrations in leukocytes, particularly neutrophils, and supports their bactericidal function. Stimulates the production and function of lymphocytes and interferes with the replication of some viruses.
• Absorption of non-heme Iron – reduces ferric iron (Fe³⁺) to ferrous (Fe²⁺), the gut-absorbable form, significantly increasing the bioavailability of plant-derived iron. Simultaneous intake of Vitamin C with non-heme iron-rich foods can increase its absorption by 2-3 times.
• Synthesis of neurotransmitters and hormones – t is a cofactor in the synthesis of catecholamines (adrenaline, noradrenaline), carnitine, and some neuropeptides.
• Support Collagen synthesis in the skin – stimulates fibroblasts to produce Collagen and inhibits metalloproteinase that degrades it. It is one of the rationales for the use of Vitamin C in nutricosmetic formulations.

Marine Collagen and Vitamin C: a necessary synergy

The combination of Marine Collagen and Vitamin C is one of the most widely used and scientifically sound combinations in skin nutraceuticals. The Collagen introduced through supplementation is hydrolyzed into peptides, which are absorbed and used as a substrate for the synthesis of new endogenous collagen. However, this synthesis requires Vitamin C as an essential cofactor. Without an adequate supply of Vitamin C, Marine Collagen supplementation produces reduced effects: the substrate is available, but the enzyme that processes it does not function optimally. The combination of these two active ingredients is therefore more effective than the sum of the two components taken individually.

Glutathione and Vitamin C: the antioxidant chain

Vitamin C and Glutathione work synergistically within the cellular antioxidant network. Reduced Glutathione (GSH) can regenerate oxidized Vitamin C (dehydroascorbic acid) back to its active form; in turn, Vitamin C preserves Glutathione from oxidation, sparing its consumption in tissues. In anti-aging and skin health formulations, the combination of Vitamin C + Glutathione + Marine Collagen is among those with the strongest rational basis.

Zinc and Vitamin C: immunity and healing

The Zinc + Vitamin C combination is the most classic in immune support formulations. The two nutrients have complementary mechanisms of action: Vitamin C supports leukocyte function and antioxidant response; Zinc is a cofactor of enzymes involved in T-lymphocyte maturation and innate immune response. Both contribute to normal immune system function with EFSA-approved claims.

The forms available for formulation

Vitamin C is available in numerous forms for supplement formulation, with relevant differences in gastric tolerability, bioavailability, and application:

• Pure ascorbic acid – the most common and least expensive form. Identical to Vitamin C produced by the body. Absorbed effectively at moderate doses (up to 200 mg per single intake). Can be irritating to the gastric mucosa at high doses or on an empty stomach.
• Mineral ascorbates (sodium ascorbate, calcium, magnesium) – salts of ascorbic acid with neutral pH. Better tolerated gastrically than pure ascorbic acid, with equivalent bioavailability. Calcium ascorbate also provides calcium; magnesium ascorbate provides magnesium-elements to be considered in the balance of the overall formulation.
• Ester-C (calcium ascorbate with metabolites) – patented form with improved gastric tolerance profile and evidence of prolonged tissue retention compared to standard ascorbic acid. Suitable for high-dose protocols.
• Liposomal Vitamin C – ascorbic acid is encapsulated in phosphatidylcholine liposomes that improve its gastric stability and transport across the intestinal wall, increasing bioavailability – particularly at high doses, where active transport becomes saturated. Data on advanced liposomal formulations show higher bioavailability than standard ascorbic acid at the same dose. Cost is significantly higher: justified in high-need settings, less necessary for ordinary daily supplementation at moderate doses.
• Vitamin C with bioflavonoids – association with citrus flavonoids (hesperidin, rutin) that in in vitro studies show synergistic effects on absorption and antioxidant activity. Clinical evidence on increased bioavailability in vivo remains mixed.

Intestinal saturation of Vitamin C occurs around 200 mg per single dose: higher doses are absorbed in decreasing percentages and excess is excreted with urine. To optimize absorption at high doses, it is preferable to divide the daily intake into several doses throughout the day rather than taking a single high dose.

EFSA Claims approved

Vitamin C has one of the largest heritages of health claims approved by EFSA under EC Regulation 1924/2006:

• «Vitamin C contributes to the normal function of the immune system»
• «Vitamin C contributes to normal Collagen formation for normal function of bones, cartilage, teeth, gums, skin and blood vessels»
• «Vitamin C contributes to normal energy metabolism»
• «Vitamin C contributes to the normal functioning of the nervous system»
• «Vitamin C contributes to normal psychological function»
• «Vitamin C contributes to the reduction of fatigue and fatigue»
• «Vitamin C contributes to the protection of cells from oxidative stress»
• «Vitamin C contributes to normal iron metabolism» – one of the few claims that make explicit the synergy with another nutrient
• «Vitamin C contributes to the restoration of the reduced form of Vitamin E» – claim formalizing the antioxidant synergy with Vitamin E
• «Vitamin C increases iron absorption»

At very high doses (greater than 1 g per day on a prolonged basis), Vitamin C may increase the risk of calcium oxalate kidney stones in predisposed individuals, and may interfere with some diagnostic tests. High doses may cause gastrointestinal effects such as osmotic diarrhea.

Always remember that it is important to consult a health care professional before starting any new supplement or treatment.