Of retinol, ruses and root veggies: The fantastic tale of carrots

Carrots and eye health have some history.

Where do carrots fall between innocuous root vegetable and sight-amplifying superfood? It may be wise to grab a snack—perhaps the obvious—before heading down this rabbit hole. 

Equal parts intrigue and lore, the presumption that carrots improve eyesight has been recycled by generations of parents encouraging children to clean their plates. However, there's more to the story than meets the eye.

Successful subterfuge  

Britain. 1940. Despite the German Luftwaffe's relentless attempt to gain air superiority, the Royal Air Force (RAF) has repelled wave after wave of daylight air assaults. With losses mounting, the Luftwaffe turns its attention to deadly nocturnal raids on population centers in a prolonged bombing campaign known as The Blitz.  

By this time, air raid blackouts were a common occurrence, as was civilian food rationing due to widespread shortages of goods. The scene is set for two separate but intertwined events to take place, explains John Stolarczyk, World Carrot Museum curator. On the one hand, the RAF has worked up something that will change history; on the other, the Ministry of Food intends to promote an easily homegrown substitute for restricted foodstuffs—carrots.  

As the Luftwaffe's tactics change to night attacks, their bombers are met by the RAF's crack pilots, such as Lt. John "Cat's Eyes" Cunningham, who rack up massive kill counts. To boost morale on the home front, Cunningham is lauded a hero, and the key to his success? A love of carrots.  

As early as 1940, researchers experimented with using high-carotene, vitamin A-rich foods to improve night vision. For its part, the RAF helps propagate Cunningham's tale. But carrots aren't the reason for the impressive tallies. It's Britain's top-secret airborne radar.  

Concurrently, the Ministry of Food launched a propaganda campaign that encouraged carrot consumption with a poignant message, "Carrots Keep You Healthy and Help You See in the Dark." It resonated among blackout-weary civilians, unaware of radar, but nonetheless seeing the RAF success.  

"The government's food ministry responded to a temporary wartime oversupply of carrots by suggesting, through propaganda, that the RAF's exceptional night-flying and target success was due to eating high-carotene content through carrots," Stolarczyk notes. "The ruse worked and public consumption of carrots increased sharply because people thought carrots might help them see better in the blackout, thus taking the pressure off other food supplies." 

The rest is history, so to speak.  

Carrots, nutritionally speaking  

World War II boosted the carrot's popularity as a nutritious superfood. It's little wonder then that the message, "Carrots Keep You Healthy and Help You See in the Dark," became "carrots help you see better."  

So, can carrots help your visual acuity? Not necessarily your visual acuity. But that doesn't mean carrots have absolutely no role in eye health. It comes down to vitamin A. This group of fat-soluble retinoids, including retinol, retinal and retinyl esters, is critical for vision. In addition to supporting a healthy cornea and conjunctival membranes, vitamin A is essential for rhodopsin. This crucial light-sensitive protein converts light into electrical signals.  

However, there's a distinction to be made when it comes to vitamin A, says Susan Summerton, O.D., a certified nutrition specialist with the Ocular Nutrition Society, and that's between preformed vitamin A and beta carotene.  

"I believe the confusion of terms with the carotenes is because humans can convert carotenes to vitamin A, with beta-carotene being most easily converted to vitamin A," Dr. Summerton says. "The conversion occurs in the upper intestinal tract, and we know our health can affect the bile salts and enzymes that are needed for this conversion."  

Preformed vitamin A (retinol) comes only from animal fats that contain active vitamin A—such as liver, eggs, buttercream or cod liver oil—whereas carrots contain beta carotene, a provitamin A that is bioconverted to vitamin A. This is important because beta carotene doesn't convert into vitamin A at a 1:1 ratio; it's somewhere in the range of 3:1 or 28:1, depending on several factors. If a person is zinc deficient, has poor thyroid function or malabsorption of fats, then beta carotene may not be converted at all.  

This is evident when looking at the U.S. Department of Agriculture's Nutrient Database. Although 100 grams of cooked carrot contain about 17,000 IU vitamin A, that's only 852 micrograms of retinol activity equivalents (RAE). Whereas, 100 grams of pan-fried beef liver contains about 26,000 IU vitamin A, or 7,700 micrograms RAE.  

What does that mean?  

"You are going to have a much better chance of absorbing and utilizing the nutrient if you eat it in the active form vitamin A (retinol) from liver or grass-fed eggs, butter and dairy," Dr. Summerton says.  

Steven Newman, O.D., board-certified nutrition specialist and Ocular Nutrition Society member, says a paradigm shift over the past two decades has trended away from the large amounts of beta carotene once thought necessary for the diet. Even pharmaceutical companies have reduced their supplemental beta carotene to around 5,000 IU.  

Typically, most Americans receive enough vitamin A in their diets, so synthetic vitamin A supplements aren't necessary and can even be toxic at moderately high doses. Dr. Newman is also bearish on carrots, considering carrots' sugar content (100 grams contains 3.45 grams of sugar) compared to spinach (100 grams contains 0.43 grams of sugar), which also contains other essential nutrients.  

"Whenever patients ask about carrots, I say, 'switch the channel, Popeye is definitely more knowledgeable than Bugs Bunny on this one,'" Dr. Newman says.  

Where does that leave carrots?  

However, carrots aren't down and out as a source of eye-healthy nutrients. For all the craftiness surrounding the British propaganda, there is science to back the link between vitamin A and night blindness, also known as nyctalopia.  

A symptom of vitamin A deficiency (VAD), nyctalopia—the inability to see well in poor lighting—is rare in Western cultures, but quite common in the developing world. Those suffering VAD lack the ability of rod cells to transform fast enough to accommodate new levels of light. Intake of vitamin A can stave off VAD and reverse nyctalopia in these at-risk populations; however, the body naturally regulates against excessive amounts of vitamin A, eventually limiting conversion of beta carotene to vitamin A.  

Additionally, in more than half of all countries, VAD is the leading cause of preventable blindness in children, affecting between 250,000 and 500,000 children annually. The World Health Organization even encourages food fortification in the form of homegrown gardens in these areas to hedge against VAD.  

So, what's the bottom line? Beta carotene-rich carrots can help eye health, especially in at-risk populations otherwise deficient in vitamin A; however, not to the same extent that the animal-based retinol form of vitamin A will help. And that doesn't phase Stolarczyk one bit.  

"Almost everyone, especially kids, likes carrots, whereas liver is an acquired taste," Stolarczyk says. "Carrots are very cheap, (easily stored) and attractively displayed in most stores. Liver looks dreadful."  

Therein lies the rub: A nutritious food that goes unconsumed does no good. Rather than honing in on a specific vitamin or nutrient, make an overall balanced diet the goal. Whether a liver lover or carrot craver, your eyes will thank you.