And propaganda can be pretty powerful.

Do Carrots Really Help You See In The Dark?, BBC Science Focus, 2013

Yes and no. Carrots contain vitamin A, or retinol*, and this is required for your body to synthesise rhodopsin, which is the pigment in your eyes that operates in low-light conditions. If you have a vitamin A deficiency, you will develop nyctalopia or night blindness. Eating carrots would correct this and improve your night vision, but only to the point of an ordinary healthy person – it won’t ever let you see in complete darkness.

The idea that it might is due to a myth begun by the Air Ministry in World War II. To prevent the Germans finding out that Britain was using radar to intercept bombers on night raids, they issued press releases stating that British pilots were eating lots of carrots to give them exceptional night vision. This fooled the British public, as well as German High Command and an old wive’s tale was born.

* The carotenoids in carrots are not technically retinol, the body converts them to retinol as needed.

A World War II propaganda poster:

One of the many advertisements that appeared during WWII that encouraged the consumption of carrots for help seeing during the blackouts. Image courtesy of Flickr user US National Archives Bot

So, the Germans started eating carrots…

There are apocryphal tales that the Germans started feeding their own pilots carrots, as they thought there was some truth in it.

And Britons started eating carrots…

the British public generally believed that eating carrots would help them see better during the citywide blackouts.

And Americans did too.

That was one bit of war propaganda that worked because I just can’t let go of the notion that eating carrots improves vision. It probably doesn’t:

Although there is a grain of truth to the claim, most people will not experience positive changes in their vision from eating carrots unless they have a vitamin A deficiency.

Are Americans deficient? The NIH says, “vitamin A deficiency is uncommon in the U.S. population.”

And really, if it’s vitamin A we’re after, a half cup of boiled spinach has more vitamin A than a half cup of raw carrots. And a sweet potato has more than 3 times the vitamin A of those carrots. Amazing how effective propaganda can be.

Image and two quotes above from:
A WWII Propaganda Campaign Popularized the Myth That Carrots Help You See in the Dark, Smithsonian Magazine, 13 August 2013
How a ruse to keep German pilots confused gave the Vitamin-A-rich vegetable too much credit