Ascorbic acid: ascorbic acid and vitamin C overview
Ascorbin is a frequently shortened term for ascorbic acid, i.e. vitamin C. The name comes from scurvy, a deficiency disease described in seafarers as early as the 18th century, which could be prevented by citrus fruits (Latin ascorbus = without scurvy). Vitamin C is an essential water-soluble vitamin: humans cannot synthesise it themselves due to a missing L-gulonolactone oxidase and therefore depend on dietary intake.
Ascorbic acid is one of the most versatile vitamins. It is an important antioxidant, cofactor of numerous enzyme reactions, involved in collagen synthesis, iron absorption, neurotransmitter formation and immune function. In medicine, ascorbic acid is used in deficiency states, in wound healing and in some special indications; in general supplementation, vitamin C is among the most-bought substances.
Mechanism of action
Ascorbic acid is a strong reducing agent and electron donor. It scavenges free radicals and protects lipids, proteins and DNA from oxidative stress. In this function it works closely with vitamin E: oxidised vitamin E is regenerated by ascorbic acid.
As a cofactor, vitamin C participates in several hydroxylases, including:
- Prolyl and lysyl hydroxylase: necessary for cross-linking collagen fibres and therefore central for connective tissue, wound healing, bone and teeth
- Dopamine beta hydroxylase: synthesis of noradrenaline from dopamine
- Carnitine synthesis: relevance for fat metabolism
- HIF prolyl hydroxylases: modulation of cellular hypoxia response
In the gastrointestinal tract, ascorbic acid promotes iron absorption by reducing Fe³⁺ to Fe²⁺. In the immune system it supports phagocyte function and lymphocyte differentiation.
Indications
- Prevention and treatment of vitamin C deficiency: scurvy is rare today but affects risk groups such as the chronically ill, alcoholics, people with restricted diets, pregnant women
- Support of wound healing and after surgery: in proven or suspected deficiency
- Increased need: pregnancy, breastfeeding, growing children, smokers
- Methaemoglobinaemia: reduction of methaemoglobin to haemoglobin in acute situations
- Iron deficiency anaemia: combined use with iron preparations to improve absorption
- Off-label high-dose therapy: in integrative oncology and in some critically ill patients as a research topic; efficacy controversial
- Topical in dermatology: anti-ageing care with photoprotective and collagen-promoting properties
Dosing and administration
Recommended daily intake (adults): 95 mg for women, 110 mg for men (DGE values), in smokers up to 155 mg. Pregnancy and breastfeeding: 105 to 125 mg.
Therapeutic use: 200 to 1,000 mg daily, orally, intramuscularly or intravenously, depending on indication and need.
Scurvy: 250 mg four times daily for several weeks, followed by a maintenance dose.
Methaemoglobinaemia: acute 1 to 4 g intravenously in emergency.
Take preferably with meals, since high doses on an empty stomach can cause gastric complaints. Enteric-coated tablets reduce gastric irritation.
Higher single doses are only partially absorbed: above 200 mg per single dose bioavailability falls markedly and the excess is renally excreted.
Side effects
At usual doses: vitamin C is very well tolerated. Side effects mostly occur with high doses.
Occasionally with high doses (above 1 g per day): diarrhoea, nausea, gastric complaints, heartburn.
Rarely with very high doses or persistent high-dose use: formation of calcium oxalate kidney stones, hyperoxaluria, haemolysis in glucose 6 phosphate dehydrogenase deficiency, iron overload in predisposed patients (haemochromatosis), elevation of uric acid with risk of gout.
Important notes:
- Before intravenous administration of very high doses (over 25 g) prior exclusion of G6PD deficiency is necessary
- In chronic renal impairment accumulation can lead to oxalate nephropathy
- Vitamin C can falsify some lab values, e.g. glucose strips, urine nitrite test or faecal occult blood
Interactions
- Iron preparations: improved absorption through reduction to Fe²⁺, useful in treating iron deficiency anaemia
- Aluminium-containing antacids: increased aluminium absorption, caution in renal impairment
- Vitamin K antagonists (warfarin, phenprocoumon): very high vitamin C doses can lower INR, INR monitoring sensible
- Cyanocobalamin (vitamin B12): very high vitamin C doses can destabilise B12
- Copper: high vitamin C doses can lower copper levels
- Chemotherapy: theoretical antagonism with bortezomib and some other substances; clinical relevance not finally clarified
- Aspirin: high aspirin doses reduce vitamin C levels
Special considerations
Pregnancy and breastfeeding: increased need, adequate intake important. Very high doses are not recommended, since theoretically rebound scurvy in the newborn is possible.
Kidney stones: in patients with calcium oxalate stones high-dose therapy should be avoided.
Haemochromatosis: risk of iron overload, avoid high vitamin C doses.
Renal function: in impaired function, accumulation and oxalate nephropathy are possible.
Glucose 6 phosphate dehydrogenase deficiency (G6PD): risk of haemolytic anaemia under high-dose therapy.
Diet over pill: for most people, a balanced diet with fresh fruits and vegetables is the best vitamin C source. Peppers, broccoli, citrus fruits, berries and sea buckthorn provide ample vitamin C in a natural matrix.
Storage: vitamin C is sensitive to light and heat. Prolonged cooking or storage causes significant loss. Freshly prepared meals best preserve vitamin C content.
Related substances
- Panthenol, provitamin B5 for wound healing
- Folinic acid, activated form of folic acid
- Colesevelam, affects absorption of fat-soluble vitamins
Frequently asked questions
Does vitamin C really help against colds?
Current studies show that regular vitamin C intake hardly affects the frequency of colds in the general population. In people under heavy physical strain (marathon runners, soldiers in cold) a slight reduction in frequency is possible. The duration of a cold can be shortened by about 8 to 14 % under vitamin C. A spectacular protective effect cannot be derived from the data.
How much vitamin C is safe?
Up to 1,000 mg daily is considered well tolerated. Higher doses are mostly excreted in stool and can cause diarrhoea. Very high doses over long periods raise the risk of calcium oxalate kidney stones. Without a specific indication, the daily recommendation of about 100 mg is sufficient.
Do I need more vitamin C as a smoker?
Yes, requirements are increased. Up to 155 mg per day are recommended, since oxidative stress under tobacco smoke uses up vitamin C stores faster.
Is vitamin C from tablets as good as from fruit?
Bioavailability is comparable. Fresh fruit and vegetables additionally supply fibre, secondary plant compounds and other vitamins that isolated tablets cannot replace. For most people, natural intake is sufficient and preferable.
Sources
- German Nutrition Society reference values
- BfArM Federal Institute for Drugs and Medical Devices
- BfR Federal Institute for Risk Assessment
- Gelbe Liste ascorbic acid monograph
Legal notice and disclaimer
The information on this page is provided for general information purposes only and does not constitute medical advice, diagnosis or treatment recommendation. It does not replace the advice of a licensed physician or pharmacist. Medicines should only be used after a doctor's prescription or pharmacy supply. All information is based on summaries of product characteristics and accepted scientific sources at the time of writing; the current SmPC of the manufacturer is always decisive. Sanoliste accepts no liability for completeness, timeliness or accuracy. In a medical emergency, dial the emergency number 112.