It's a lie and has been completely deboonked. Anyone who says this in 2022 should be embarrassed.
In WW2 the allies had deployed radar technology without Germany's knowledge. This allowed the allied pilots to be aware of German fighter planes in the dark from great distances. Naturally this would raise suspicions, so the british media falsely reported a scientific discovery about a link between Vitamin A and good eyesight, especially at night, and they were now feeding their pilots large amounts of carrots to gain a combat advantage.
