You probably grew up hearing that eating carrots could help your eyesight— even make you see in the dark. That would be nice, except it’s not entirely true (unless you have one heck of a vitamin deficiency). The idea that carrots can give you supervision has been traced back to wartime 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 isn’t actually that far from reality, though. Like all good lies, it’s 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 A— a 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? That’s Vitamin A. In the back of your eyes are rod photo receptors— cells that need the fat-soluble molecule 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, you’d better eat up. If you want to go caving, however, you’re 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 A’s 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 United States 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, West says, and they’d 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 his or her liver reserves for a few days, there are plenty of staple foods in the U.S. 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 they’re 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 can’t actually correct the vision we’re born with, and it certainly can’t 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 don’t 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.