By Jennifer Chaussee for Wired .

You probably grew up hearing that eating carrots could help your eyesighteven make you see in the dark. That would be nice, except its not entirely true (unless you have one helluva vitamin deficiency). The idea that carrots can give you supervision has been traced back to war time lies the British apparently made up to fool the Germans into thinking their pilots had developed so-called night sight, from all the carrots they were eating. In fact, it was the first iterations of radar technology that the British were using to see enemy planes that approached in the dark, not root veggies.

The myth that made its way to your childhood kitchen table isnt actually that far from reality, though. Like all good lies, its surrounded by a hard (shall we say, crunchy?) shell of truth.

Yes, carrots do have a hefty dose of beta-carotene, which your body converts into vitamin Aa molecule that helps with a variety of basic eye functions. Ever walk into a dark movie theater on a sunny day and notice how your eyes adjust to seeing in the dark after a few minutes? Thats Vitamin A. In the back of your eyes are rod photo receptorscells that need the fat-soluble molecule in order to help you see in low light. A bunch of other vegetables do the same thing for you, though, so if you want to avoid bumping into people at the theater or, say, stave off cataracts, youd better eat up. If you want to go caving, however, youre better off taking a headlamp than a bundle of carrots.

In countries where people are extremely deficient in vitamin A, supplements have been known to help improve poor eyesight, especially in the dark, but this is only in cases where vision problems were prompted by poor nutrition in the first place. In countries where the food system is less sophisticated and we see crushing poverty, the margin between harvest season and hungry season is palpable, says Keith West, a public health professor at Johns Hopkins Bloomberg School of Public Health who studies Vitamin As role in the body. These populations can dip into actual deficiency with Vitamin A, especially in respect to young, growing children who can become what we call night blind.

In the US and other developed, well nourished countries, the average person would have to stop eating any Vitamin A for a month or several months before they became truly deficient, says West, and theyd have to work hard at it. The body stores the molecule in the liver, which doles it out to the rest of the body only as needed and keeps the rest for later. Even if someone has to dip into their liver reservers for a few days, theres plenty of staple foods in the US that are rich in Vitamin A or at least fortified with it, including milk. So, extreme deficiency is rare, especially among children. If you really know your vitamins, you know that low-fat and skim milk loses its vitamin A in processing, but dairy producers put it back in afterward, so people usually get plenty of it during the crucial years of development even if theyre not drinking milk or eating carrots every day. As a result, just 6 percent of kids are deficient in vitamin A, according to the Environmental Working Group.

For the rest of us, vitamin A cant actually correct the vision were born with and it certainly cant give us ultra night vision, because your body can only convert so much beta-carotene at once. When you drink too much carrot juice, for example, your body stops converting that beta-carotene, which by itself is a pigment, into Vitamin A, so the excess accumulates in the fat just beneath your skin, giving it an orange glow. On the paranoid end of the spectrum, too much vitamin A can actually be toxic. Overloading your system with supplements when you dont have a deficiency can make your hair fall out or worse, overwhelm and damage your liver. So, think of carrots as a tool for maintaining healthy eyes rather than a biohack for radar-quality night sight.

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