My three favorite vegetables are: carrots, spinach, and kale.

I eat about 6-7 servings of vegetables a day generally, and at least four of the servings include the aforementioned specifically. This means that I consume the proverbial Upper Limit of vitamin A.

Am I at risk?

– Julia Rhine
(Location Unknown)

Absolutely not!

Although the term “vitamin A” is used to describe a particular nutrient available both in plant foods (i.e.: carrots, spinach, pumpkin, kale, lettuce) and animal foods (i.e.: eggs, liver, full-fat dairy), the story is a little more complicated.

Vitamin A in animal foods is available to us as retinol, also known as “preformed vitamin A”.

Plant sources, however, contain carotenes (of which there are over 600, including the ever-popular beta-carotene), which are then converted into retinol by our bodies.  Some carotenes are converted very efficiently; others are not.

As I always like to say, our bodies are smart.  Individuals with low vitamin A stores, for instance, convert carotenes into retinol much more efficiently than those with sufficient stores.

Even when dealing with beta-carotene (the most efficiently converted carotene), you are looking at significantly reduced bioactivity in comparison to retinol.  It takes 12 micrograms of carotenoids from food to equal one microgram of retinol.

I specifically say “from food” because carotenoids in supplement form are more bioactive.  In their case, two micrograms are equivalent to one microgram of retinol.

Let’s talk toxicity now.  While high amounts of retinol can be toxic, that is not the case with carotenoids.

The only issue that arises as a result of consuming a high amount of carotenoids from food is your skin turning a yellow-orange color.  The most likely reason for this is that, as stated previously, if our vitamin A stores are high, carotenoid conversion is brought down several notches.

Consume a diet that is consistently very high in in the pure retinol form of vitamin A, however, and expect liver problems as well as bone mineral density issues.

Remember, since vitamin A is a fat-soluble vitamin, it is stored in the body; toxicity is not simply solved by drinking massive amounts of water and urinating large quantities out.

What makes all of this even more (!) complicated is that while there are Recommended Dietary Allowances set for vitamin A, there aren’t any for carotenoids.

So, then, how do vegetarians and vegans know how much plant-based “vitamin A” to consume?

Well, one milligram of beta-carotene is equivalent to approximately 1,667 International Units of vitamin A.

One medium sweet potato, for example, packs in 13 milligrams of beta-carotene — 21,671 International Units of Vitamin A.

To convert International Units of vitamin A from plant foods into retinol equivalents, we simply multiply that figure by 0.1 and end up with 2,167 REs of vitamin A.

Considering that adults need 2,310 (if female) to 3,000 (if male) International Units of vitamin A a day (that’s 700 and 900 REs, respectively), then that one sweet potato provides plenty.

Some confused individuals claim that the lack of retinol in plant sources of vitamin A “prove” they are inferior sources, and that we should strive to get all of our vitamin A from animal sources.

WRONG!  They (conveniently?) forget that carotenoids are phytonutrients, which means they contribute many healthful qualities.  Research has clearly demonstrated that diets rich in beta-carotene help lower heart disease and lung cancer risk.

So, dear Julia, keep enjoying those vegetables!  Remember, though, to consume them in a meal that contains at least 4 grams of fat to ensure proper absorption!