When you think of getting enough vitamin A, what is the first food you think of? Carrots? Sweet potato?
You might be surprised to know that neither of these contain a single molecule of vitamin A, nor do any plant foods.
Beta Carotene vs. Vitamin A
Bright orange foods like these contain beta carotene, one form of carotenoids.
Carotenoids are not vitamin A but rather a precursor called provitamin A that must be converted to vitamin A by the body. An enzyme in the intestine breaks down carotenoids so they can be converted into their active form.
Actual vitamin A, known as preformed vitamin A, is found only in animal foods. Preformed vitamin A includes retinol and retinyl esters. The free form, retinol, is not typically found in foods - retinyl esters like retinyl palmitate are the form found in animal foods.
Plant foods contain hundreds of types of carotenoids, but only around 10% of those can be converted to retinol. Within those 10%, carotenoids can be converted to varying degrees.(1)
Can Beta Carotene Be Absorbed?
The typical vitamin A quantity you'll see listed on nutrition labels is mcg (micrograms) or IU (vitamin A international units). However, these measurements do not reflect the bioavailability of the vitamin A used.
Plant forms of vitamin A such as beta carotene are converted at a rate of 3.6-28:1 by weight. That means that just 1/28th of the beta carotene you consume may actually be turned into retinol! In raw carrots, only 2% of the beta carotene consumed was shown to be converted.
You can find the Retinol Activity Equivalent (RAE), which is the equivalent amount of vitamin A in plant foods, by searching for them on the USDA's Food Data Central. (3)
The story about beta carotene gets even more complicated. Not everyone converts carotenoids to retinol equally!
Vitamin A Impaired Conversion
A number of factors influence our ability to convert carotenoids to vitamin A. It's impacted by thyroid health, gut health, alcohol intake, and like most thing: genetics.
Carotenoids are converted by an enzyme called β-carotene 15,15′-monooxygenase (or BCMO1). This enzyme converts carotenoids to retinal, which is then converted to retinol.(4)
Around 45% of the population has a genetic variation that causes reduces enzyme activity on the BCMO1 gene responsible for this conversion. In fact, having this genetic variation reduces conversion by as much as 70%! (5)
How to Know If You're a Vitamin A Low Converter
Do you have a 23andMe account? If so, great news: you can use it as a tool to find whether you're a low converter.
In the chart below, you can find the polymorphism to search for. Simply type it into the search bar, press "enter" and click "marker", and look for the letter in question under "Your Genotype":
How Do I Get Enough Vitamin A?
Whether you're a low converter or not, the safest bet is to consume animal products, especially organ meats (beef liver is the best source, followed by cod liver oil), to ensure you're getting enough vitamin A.
If you're vegetarian or just not a big fan of organ meats, you can take a supplement like Why Not Natural's pure vitamin A in MCT oil. It's completely vegan, and the same form of vitamin A found in animal products (retinyl palmitate).
(2) Bioaccessibility of Carotenoids and Vitamin E from Their Main Dietary Sources
Emmanuelle Reboul, Myriam Richelle, Eloïse Perrot, Christiane Desmoulins-Malezet, Victor Pirisi, and Patrick Borel
(4) Mechanisms of Carotenoid Intestinal Absorption: Where Do We Stand?