Ascorbic Acid (Vitamin C)

How it works

It is an essential cofactor for collagen synthesis and several enzymatic hydroxylation reactions and acts as a water-soluble antioxidant.

Prescribing in practice

• Prolonged high-dose use can predispose to oxalate renal stones and may be hazardous in patients with renal impairment or a history of oxalate calculi.
• Reserve treatment for genuine deficiency, which is uncommon other than with poor diet, malabsorption or increased requirements.
• Vitamin C can interfere with some laboratory and point-of-care tests, including blood glucose and urinalysis results.

Monitoring

Monitoring is usually clinical, based on resolution of deficiency features; specific laboratory monitoring is not routinely required.

Counselling the patient

• A balanced diet usually provides enough vitamin C.
• Avoid taking very high doses long term without advice.
• Tell your clinician if you have had kidney stones.

Evidence & guidelines

Vitamin C is established treatment for scurvy and deficiency, while evidence does not support routine high-dose use to prevent or treat common colds.