The basis for this "old wive's tale" is that, accurately, carrots as well as other yellow/orange vegetables and gourds (squash, pumpkin) are fantastic sources of vitamin a, an essential vitamin required for photoreceptor (cone/rod) metabolism. While severe vitamin a deficiency may lead to serious, but generally reversible, vision problems, such as night blindness, most people in developed countries meet more than their daily vitamin a requirements from normal diets and there is no need to consume exorbitant amounts of carrots.