Vitamin A (retinol)
A fat-soluble vitamin essential for vision, immunity, reproduction and skin health, found as preformed vitamin A (animal) and as provitamin (plant beta-carotene).
Vitamin A comes in two forms:
- Retinol (preformed vitamin A): directly usable, found in animal products (liver, eggs, butter, oily fish)
- Beta-carotene (provitamin A): found in coloured plant foods (carrot, sweet potato, spinach), converted into vitamin A by the body
The original angle (the capricious conversion): people believe that eating carrots guarantees vitamin A. An important nuance: the conversion of beta-carotene into retinol is variable and often inefficient. It depends on genetics (some people convert poorly), zinc status, the presence of fat, and state of health.
Vegans and people with low conversion can therefore be short of “active” vitamin A despite eating plenty of orange vegetables. A little-known point to watch.
Fat-soluble absorption: as beta-carotene is fat-soluble, you need to eat it with fat to absorb it well (grated carrots + oil, sweet potato + butter). Eating a raw carrot with no fat = poor absorption.
The cooked carrot paradox: cooking breaks down cell walls and increases the bioavailability of beta-carotene (cooked carrots > raw for vitamin A). Another case where cooking is beneficial.
The danger of excess (retinol): unlike beta-carotene (converted on demand, with no risk of overdose), excess preformed retinol is toxic (being fat-soluble, it accumulates). Beware of over-supplementation and of liver (very rich) in pregnant women: too much vitamin A is teratogenic (it causes malformations). Beta-carotene does not carry this risk.
Key functions: night vision (deficiency causes night blindness, the leading cause of preventable blindness in the world), immunity, and the integrity of mucous membranes and skin.