Vitamin A

How it works

Retinol and its active metabolites (retinal and retinoic acid) support rhodopsin-mediated vision and act on nuclear retinoid receptors to regulate gene transcription governing cellular differentiation.

Prescribing in practice

• Excess vitamin A is teratogenic, so high-dose supplements must be avoided in pregnancy and in women who may become pregnant, in line with MHRA advice.
• It accumulates in the liver and chronic excess intake can cause hypervitaminosis A, so combined sources should be considered to avoid cumulative overdose.
• Use with caution in hepatic impairment and in patients with raised intracranial pressure, as toxicity can exacerbate these states.

Monitoring

Clinical response and features of toxicity (skin, hepatic and neurological) guide monitoring rather than routine vitamin A level measurement in most settings.

Counselling the patient

• Do not take additional vitamin A supplements or liver-rich foods without advice if pregnant.
• Report headache, visual disturbance, dry skin or bone pain, which may indicate excess.

Evidence & guidelines

Vitamin A supplementation is a long-established intervention for deficiency states and is supported by WHO and UK public health guidance.