Vitamin A can have a bad reputation, even though it’s an essential, fat-soluble vitamin which plays a vital role in growth, immunity, and hormone production. (1,2,3) It works in tandem with other fat soluble vitamins, and special care must be taken of its proportion to vitamin D3.(4) This is at the root of vitamin A’s disrepute: a large dose of vitamin A can have a negative effect if one suffers from vitamin D deficiency. Vitamin A has two main types: retinol, found in animal products, and carotenoids, found in plants. Humans can convert carotenoids to retinol, although this process can be restricted by certain gene mutations and malabsorption.(5)

What does vitamin A deficiency cause? 

While severe vitamin A deficiency is rare in developed countries, it can easily develop if one does not consume vitamin A rich food.(6) This condition leads to deteriorated night vision, but luckily it can be reversed with vitamin supplements if it is recognized in time.(7) Furthermore, vitamin A deficiency can lead to skin, eyes, and mucus membranes becoming dry and susceptible to injury, which increases the risk of infection.(8) Children with vitamin A deficiency can cause growth problems, and later hormonal imbalances as well.(1,3) 

What are good sources of vitamin A? 

Liver is the only natural food source containing a significant amount of vitamin A in the form of retinyl palmitate which the human body can utilize very well. This is no surprise, since many animals, just like us, store vitamin A in their liver.(9) While several products of animal origin, such as egg yolk or butterfat contain vitamin A, they do not contain the necessary amount.  

Plant-based vitamin A can be found in carotenoid-rich vegetables and fruits, such as carrots, pumpkin, or cantaloupe. We could cover our daily intake if we could transform 100% of the carotenoids they contain into vitamin A. The problem is that our genetics and digestive system both influence this transformation, therefore we cannot be certain how much vitamin A we gain through solely plant-based products. (5) It’s recommended to consume these foods with something fatty to increase the amount of absorbed carotenoids.

How best to take vitamin A? 

If you eat 150-200 g of liver weekly along with some carrots, pumpkin, or sweet potatoes every now and then you almost definitely get enough vitamin A. However, those who do not eat liver should replace some vitamin A in the form of retinyl palmitate depending on how much carotenoid-rich vegetables they eat and what their vitamin D3 intake is. The proportion of vitamins A and D3 is ideally 1:1, or a slightly higher intake of vitamin A. For most people, it means 4000 IUs of both vitamins A and D3 daily. It’s recommended to take the same amount of vitamin A as vitamin D3 if one rarely eats liver or carotenoid-rich vegetables: this way, you can be certain that your intake has the right dosage regardless of your diet. Since vitamin A is stored in the liver, you do not have to take it every day: a weekly dose is enough. 

Can vitamin A be overdosed? 

Since the body stores vitamin A and cannot get rid of the surplus, taking a high dosage can result in overdose over time. However, this is extremely rare: to experience symptoms, one should be taking a high dosage of retinyl palmitate, the natural, fat soluble form of vitamin A for months. In contrast, synthetic, water-soluble forms of vitamin A, such as retinyl acetate, can lead to poisoning in only a few weeks with one tenth of the dosage.(10) Another common issue is taking large amounts of vitamin A without vitamin D3. This increases the risk of broken bones, presumably because the practice decreases the already low levels of vitamin D.(11) Taken separately, they can mutually decrease each other’s levels, but taking them together in the right dosage can not only help increase their beneficial qualities, but it can help prevent overdose. 

Fun fact 

The highest concentration of vitamin A can be found in the liver of polar bears, which contains over 20.000 IUs of vitamin A in a single gram. Arctic explorers have observed that when they ran out of food and were compelled to consume polar bear liver, many became sick. No wonder, since a 200 g portion contains over 5 million IUs of vitamin A, which is one thousand times the recommended daily intake.(12) The first documented case dates back to 1596, when multiple people fell ill after consuming polar bear liver, although they did not know about vitamin A yet. It’s nearly impossible to overdose vitamin A from the food we typically eat, especially if one pays attention to restoring vitamin D3.  

[The cover photo of the note shows butter. 100 grams contain 2499 IU of vitamin A, which provides little over half of the required daily amount.]