Cats, Carotenoids, and Carrots

As gentle as Benjamin appears, he's a carnivore, not an omnivore like us. Blame it on vitamin A.

This is vitamin A:


Preformed vitamin A, which refers to retinol, retinaldehyde, and retinoic acid, can only be found in animal products. It’s not found in plants – but that doesn’t mean vegetarians lack vitamin A in their diets.

This is beta-carotene:


Cut it in half and you have two vitamin A units. Humans produce an enzyme called 15, 15’-dioxygenase which cuts the beta-carotene into two vitamin A units; therefore, beta-carotene can function as a provitamin, a precursor to a vitamin. Cats don’t have this enzyme so they can’t convert carotenoids into vitamin A. They have to eat preformed vitamin A, meaning they can’t remain healthy on plant foods alone.

Vitamin A is necessary for proper vision, cell growth and division, reproduction, and immunity. The RDA for Vitamin A is 700 RE (retinol equivalents) for women and 900 RE for men. When you see vitamin A on packaging for plant foods, it’s really a listing of the provitamin A content and the estimated conversion rate of the carotenoids to retinol.

Vitamin A is a fat-soluble vitamin, which means we store it in our tissues, including in our liver. We can consume too much vitamin A, unlike carotenoids, and accumulate vitamin A in our bodies to toxic levels. In school, we read about a researcher who ate an entire polar bear liver (don't ask why) – and died from a vitamin A overdose!!!! Moral of that story is don’t eat polar bear liver.

What about those people who drink so much carrot juice that they turn orange? This condition called carotenodermia, which occurs after high consumption of carotene-rich foods, is non-toxic and goes away once consumption is reduced. In fact, it may be protective since the body has limited the conversion rate to vitamin A, preventing a toxic overdose.

Yes, carotenoids are named after carrots. And yes, carrots are high in beta-carotene. When I was a little girl, my mother told me eating carrots was good for my eyes. Every Saturday morning, I’d plant myself in front of the TV with a bag of carrots to watch Bugs Bunny. Every time Bugs ate a carrot, I ate a carrot. Today I am glasses-free as is Bugs.

There are approximately 600 types of carotenoids, a category of fat-soluble pigments found in veggies, fruits, and flowers. Of those, about 50 or so have some provitamin A activity with beta-carotene having the highest rate of conversion to vitamin A.

Carotenoids have benefits beyond conversion to vitamin A which may be why our bodies only convert so much of it. Carotenoids can act as powerful antioxidants in their original carotenoid configurations.

So eating colorful veggies gives you both vitamin A and carotenoid benefits. And get those carotenoids from food. Supplements may give you too much of a good thing at once, as demonstrated by a study showing higher rates of lung cancer in high-risk men given beta-carotene supplements. This may be because no antioxidant works in isolation. Antioxidants packaged in plants work with other substances in that same plant. When isolated in supplements, protective antioxidants may convert into destructive pro-oxidants since they are missing their yet unidentified nutrient partners. Plus veggies just taste good.

By the way, there are some vitamins that we have to eat whole that our pets don’t need. Dogs and guinea pigs make L-gulonolactone, an enzyme that allows their bodies to make vitamin C. We don’t have it so we have to eat vitamin C. Another good reason to eat your fruits and veggies.