What is vitamin A?
Vitamin A is not just a single substance. When it comes to diet, there are two main groups: preformed vitamin A (retinoids) and provitamin A (carotenoids).
What's the difference between preformed vitamin A and provitamin A?
Preformed vitamin A can be found in animal-based products and provitamin A can be found in plant-based products. Our bodies turn provitamin A into vitamin A. However, BOTH of them must be metabolized into their active forms (retinal and retinoic acid) before they can carry out their biological functions. Our body cells are pretty good at this kind of stuff.
To make the two forms comparable, dietary recommendations give you RAE-values (retinol activity equivalents). So if you ever see that on a food label, you can pull this unnecessary knowledge out of the hat.
How much of it do I need?
Ladies need about 700mcg RAE (and an extra 70mcg during pregnancy), gentlemen about 900mcg RAE.
What foods contain vitamin A and how much of them do I need to eat per day?
Your parents have probably told you to eat your carrots when you were a child. Usually, carrots are a symbol for vitamin A and rightly so. A single medium-sized carrot contains enough (pro)vitamin A to get you through the day. Red peppers are also a good source of vitamin A. However, one of the best sources of vitamin A are sweet potatoes. One baked sweet potato contains about five times the vitamin A that is recommended per day.
If you're more into animal-based stuff, beef liver and fish also contain vitamin A.
What happens if I don't get enough vitamin A?
Vitamin A deficiency is unfortunately common in developing countries because foods containing preformed vitamin A or provitamin A are either not available or too expensive.
The most common symptom of vitamin A deficiency is called xerophthalmia. This condition makes you lose the ability to see in low light. If it isn't treated, you can even go blind. So when parents tell their kids to eat carrots because they are "good for their eyes", they are right.
Can an overdose of vitamin A also be harmful?
This is the second major difference between preformed vitamin A and provitamin A. Your liver can store excess vitamin A. According to the U.S. Department of Health and Human Services, large amounts of provitamin A are not associated with major adverse effects, while excess preformed vitamin A can have significant toxicity.
Symptoms of chronic excess preformed vitamin A intake include nausea, headaches, dizziness and pain in joints and bones. Severe excess intake can lead to coma and even death. The latter cases are mostly associated with excess preformed vitamin A intake from food supplements. Arctic explorers have also experienced acute symptoms after eating polar bear liver.
The worst part is, though, liver damage due to excess vitamin A intake may not be reversible.
Does it have any other effects?
As mentioned before, vitamin A deficiency is common in developing countries. During measles outbreaks in Africa, studies have shown that infected children who were given high oral doses of vitamin A had much lower mortality of measles than vitamin A deficient patients.
I hope you liked this episode of nutrition facts. Thanks for reading. Eat carrots. They are good for you.