Vitamin C ascorbic acid

Mechanism of action

1) Enzymatic cofactor: it keeps iron in its reduced state (Fe2+) for the activity of prolyl/lysyl hydroxylase in collagen synthesis; it supports enzymes involved in carnitine synthesis and certain neurotransmitter biosynthesis pathways. 2) Antioxidant/redox buffer: it donates electrons by neutralizing reactive oxygen species (ROS) and regenerates other antioxidants (e.g. vitamin E) in specific contexts. 3) Immune modulation: it supports barrier functions, chemotaxis, and leukocyte activity; it may reduce the impact of oxidative stress associated with infections and high physical loads. 4) Non-heme iron absorption: it reduces Fe3+ to Fe2+ in the intestinal lumen, increasing the bioavailability of dietary iron.

Supported benefits

• Reduced duration of common cold symptoms in the general population (modest average effect) and reduced incidence in individuals exposed to intense physical stress (e.g. endurance athletes, military personnel) in some studies (strong)
• Prevention and treatment of vitamin C deficiency (scurvy) and support for collagen synthesis with improvement in signs/symptoms related to deficiency (strong)
• Increased absorption of non-heme iron when taken with meals rich in plant-based iron (useful in specific dietary contexts) (moderate)
• Reduction in markers of oxidative stress and inflammation in some contexts (variable results; depends on nutritional status, dose, and population) (moderate)
• Support for endothelial function/blood pressure with small average effects in some meta-analyses (high heterogeneity) (limited)
• Muscle recovery/DOMS: possible small effects on soreness or damage markers in some studies, but inconsistent results and potential interference with training adaptations if used chronically at high doses (limited)

Safety & side effects

• Dose-dependent gastrointestinal disturbances: nausea, cramps, diarrhea, heartburn
• Increased urinary oxalate in some individuals (relevant to stone risk in predisposed people)
• Possible interference with some laboratory tests (e.g. capillary blood glucose with certain glucometers, tests based on redox reactions)
• In individuals with G6PD deficiency: high doses (especially parenteral) have been associated with a risk of hemolysis; with oral use the risk is lower, but caution is still warranted

FAQ

Does vitamin C directly improve athletic performance?

Direct effects on performance (time, power, VO2max) are generally small or inconsistent. The main interest in sports concerns immune support during periods of stress and its role in collagen, especially if dietary intake is insufficient.

Are megadoses of vitamin C always better for immunity?

No. Absorption is saturable and the excess is eliminated. High doses increase the risk of gastrointestinal disturbances and, in predisposed individuals, kidney problems. In addition, a chronic excess of antioxidants can interfere with adaptive training signals in some contexts.

Does it make sense to take it only when you get sick?

In studies on the common cold, regular intake tends to reduce the duration of symptoms; starting only at onset may have more variable benefits. In any case, the average effect is modest and depends on the context.

Vitamin C and collagen: is it a useful combination?

There is a biochemical rationale because vitamin C is necessary for collagen synthesis. The evidence on structural improvements (tendons/ligaments) with supplementation in non-deficient individuals is still heterogeneous; adequate dietary intake remains central.

Can it increase the risk of kidney stones?

In some predisposed people, high doses can increase urinary oxalate and the risk of stones. The risk depends on clinical history, hydration, diet, and kidney function.