Retinol (aka Vitamin A) is a highly important essential vitamin for various processes and functions of the body. Do not confuse retinol with beta-carotene, as beta-carotene is not technically a usable form of vitamin A, but a precursor. Theoretically, beta-carotene should convert into retinol, but many people either have a very low capacity to do this or lack the ability to do so completely. This means that plant sourced "vitamin A" in the form of beta-carotene may not actually be a suitable source for much of the human population. Those on plant based or vegan diets should consider either getting themselves tested for genes associated with proper conversion or taking a retinol supplement, as usable retinol which does not require conversion only exists in animal products or synthetic forms. The RDA for vitamin A is set at 5000 IU for adults. A much higher amount of beta-carotene would be required to meet this need assuming that a person's genetics allow them to make the conversion properly. Even then, the super high carotenoid content of the diet could cause hypercarotenemia.
There have been concerns over vitamin A toxicity, but this has only been demonstrated in cases of mega dosing supplements or consumption of animal livers with extraordinarily high retinol content (i.e. polar bear liver). Beta-carotene is considered non-toxic in high amounts, but will make you look like an oompa loompa. Consumption of ruminant liver for vitamin A is unlikely to cause toxicity in normal amounts.
Retinol is fat soluble, and therefore should be consumed with a fat containing meal for proper absorption. Unlike water soluble vitamins, your body can build up stores of retinol in adipose tissue (fat cells).
The importance of retinol can not be understated. These are not the only functions, but it is crucial to obtain adequate amounts in order to achieve optimal health and proper bodily functioning. Vitamin A deficiency is rare in developed countries where animal product consumption is high, but quite rampant in underdeveloped nations where animal sources are scarce. This is one of the reasons that the charitable organization Vitamin Angels exists and why they primarily provide vitamin A supplements.
Proper growth in children
Sexual maturation and fertility
Essential for vision (especially night vision)
Needed for proper cell differentiation
Required for immune functioning
Proper bone development
Primary deficiency symptoms and diseases
Improper growth and development in children
Lowered immune functioning
Poor skin quality
Slow wound healing
As touched on in the opening paragraphs, animal sources of vitamin A are the only technically usable forms and many people lack the ability to convert beta-carotene into vitamin A. Plant sources cannot be considered a reliable source unless gene expression is present for conversion, therefore the plant sources listed will be beta-carotene sources and not applicable to all people.
Liver and organ meat
Fatty animal meats
Sweet potato (beta-carotene)
Green leafy vegetables (beta-carotene)
Vitamin A supplements are very nuanced. On one hand, they can easily correct a deficiency, but excess amounts can easily become toxic to the liver whereas food sourced vitamin A will rarely cause toxicity. Supplements should be used wisely and never mega dosed, but should be considered by those wishing to consume a plant based or vegan diet who have not been assessed for the genes for proper conversion of beta-carotene to retinol.
Non-defatted liver supplements
Who needs it most?
Those who consume little to no animal products and do not have the genes for proper conversion of beta-carotene to retinol
People with low immune system functioning or who have infections
Children in developing countries with low access to retinol in the diet
Consuming liver a few times per week will provide adequate retinol
Liver pills will generally only provide ample vitamin A if the supplement has not been defatted
Always consume vitamin A with fats for proper absorption
Be very careful with vitamin A supplements, as they can become toxic quite quickly in high amounts