Vitamin A (retinol) is a fat-soluble vitamin essential for vision (particularly night vision and photoreceptor function), immune defence (epithelial barrier integrity and immune cell differentiation), skin health, and foetal development. It is obtained from animal foods as preformed retinol and from plant foods as beta-carotene (provitamin A), which is converted to retinol in the body.
Vitamin A deficiency is the leading cause of preventable blindness globally, but is uncommon in well-nourished Australians. Toxicity from excessive supplementation (hypervitaminosis A) is a significant concern because vitamin A is stored in the liver: symptoms include headache, liver damage, bone abnormalities, and severe teratogenicity in pregnancy.
FAQs
Is it safe to supplement vitamin A?
At moderate doses (700-900 mcg retinol equivalents per day as part of a multivitamin), vitamin A is safe. High-dose preformed vitamin A supplements (above 3000 mcg/day) carry toxicity and teratogenicity risks. Beta-carotene from food does not cause toxicity.
Does beta-carotene convert to vitamin A efficiently?
Conversion is variable and inefficient — approximately 6-12 mcg of dietary beta-carotene is needed to produce 1 mcg of retinol. Conversion is reduced in people with thyroid disease, diabetes, and certain genetic variants.
What is the first sign of vitamin A deficiency?
Night blindness (difficulty seeing in low light) is the earliest and most sensitive clinical sign of vitamin A deficiency. Dry eyes (xerophthalmia) and Bitot's spots develop with more severe deficiency.
Can too much vitamin A damage the liver?
Yes. Chronic hypervitaminosis A causes hepatotoxicity, fibrosis, and portal hypertension in severe cases. Liver damage is a key sign of vitamin A toxicity.
