Vitamin C
Antioxidant vitamin essential for immunity and collagen synthesis
What is Vitamin C?
Vitamin C (ascorbic acid) is a water-soluble essential vitamin — humans cannot synthesise it (unlike most mammals) due to a non-functional gene for the final enzyme in ascorbic acid synthesis (GULO). It's a powerful antioxidant, a cofactor for collagen synthesis enzymes (prolyl hydroxylase and lysyl hydroxylase), and essential for carnitine synthesis (required for fatty acid oxidation), neurotransmitter production (dopamine, noradrenaline), and immune cell function.
How it works
As a reducing agent, vitamin C donates electrons to neutralise free radicals and regenerate other antioxidants (vitamin E, glutathione). In collagen synthesis, it's required to hydroxylate proline and lysine residues — without which collagen triple-helices are unstable. In immune function, vitamin C accumulates in neutrophils and macrophages at concentrations 100x higher than plasma, supporting their killing and mobility. It also stimulates production and activity of natural killer cells and lymphocytes.
What the evidence shows
Immune: A 2013 Cochrane review (29 trials, 11,306 participants) found vitamin C (200mg+) reduced cold duration by 8% in adults and 14% in children. Megadose vitamin C at cold onset may further reduce duration. Collagen/skin: multiple RCTs show improved skin elasticity and wound healing with supplementation. Iron absorption: consistently and significantly enhances non-haem iron absorption. Cardiovascular: epidemiological data shows inverse association between vitamin C status and cardiovascular events.
When to expect results
Plasma vitamin C levels rise quickly — it's one of the fastest-acting supplements. Antioxidant defence improving immediately.
Cold symptoms shorter and less severe if taken at onset. Energy and mood improving in those who were deficient.
Collagen synthesis support becoming apparent. Skin quality and wound healing improving.
Sustained antioxidant protection and immune support. Long-term collagen structural benefits accumulating.
Dosing
UK RNI: 40mg/day. Typical supplement doses: 250–1,000mg/day. Bioavailability plateaus around 200–400mg — above this, absorption decreases and excess is excreted. Divided doses improve retention. For immune support during illness: 1,000–2,000mg in divided doses. Bowel tolerance dose varies per individual — excess causes loose stools.
Forms to choose
Ascorbic acid: the standard form, most cost-effective, highly bioavailable. Buffered forms (sodium ascorbate, calcium ascorbate): gentler on the stomach, useful for sensitive stomachs or high doses. Liposomal vitamin C: enhanced absorption by enclosing ascorbate in phospholipid vesicles — useful for achieving higher plasma levels without GI side effects. Acerola cherry: natural, concentrated food source. Rose hip: contains ascorbic acid plus bioflavonoids.
Who benefits most
Virtually everyone during winter months (when fresh fruit/vegetable intake often declines), smokers (smoking depletes vitamin C significantly — needs are 35mg/day higher), athletes (antioxidant demand is elevated during intense training), people taking iron supplements (dramatically enhances absorption), those with slow wound healing, anyone with high oxidative stress.
Who should avoid / caution
People with haemochromatosis (enhances iron absorption — dangerous when already iron-overloaded). Those with oxalate kidney stones should keep doses moderate. G6PD deficiency: avoid very high IV doses (not a concern with standard oral supplementation).
Interactions & stacking
Vitamin C enhances non-haem iron absorption by up to 3x. Always take iron supplements with vitamin C or orange juice.
Vitamin C is required for collagen cross-linking. Taking both together maximises collagen synthesis stimulation.
Classic immune-support combination with additive effects on immune cell function and antioxidant defence.
Some research suggests very high antioxidant doses immediately post-exercise may blunt exercise adaptations (mitochondrial biogenesis). Use normal doses rather than megadoses around training.
Safety & side effects
Very safe at normal doses. High doses (above 2g/day): diarrhoea, GI upset — use buffered forms or liposomal. In people with G6PD deficiency, very high IV vitamin C can cause haemolysis (this is not a concern with oral supplementation). High-dose vitamin C may theoretically increase oxalate kidney stone risk — those prone to stones should moderate.
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This information is for educational purposes only and does not constitute medical advice. Always consult your GP or a qualified healthcare professional before starting any new supplement, particularly if you are pregnant, breastfeeding, have a medical condition, or are taking prescription medication.