Do carrots help you see in the dark?
Unlike some of the more tenuous claims parents make in the ongoing battle to get their kids eating vegetables, this one is quite true.
The key is vitamin A, or retinol. We need retinol: animals can’t synthesise it themselves so rely on getting it in food. The typical omnivorous human gets about 80% of their retinol from carotenoids (that’s right, from “carrot”) in fruit and vegetables. Carotenoids occur throughout the plant world as red, orange and yellow pigments, but green leaves are full of them, too — they’re what make leaves yellow in autumn as the green fades.
Beta-carotene, the orange substance that gives carrots their colour, is the most important of these for satisfying our unending need for retinol. Carrots certainly aren’t the only source in our diets, but they are an exceptionally good one.
Retinol is used widely around the body during development and throughout life. It’s importance to eyesight, though, is betrayed by its name which is derived from the word “retina”.
The retina, lying right at the back of the eye, contains the photoreceptors, the cells responsible for actually detecting light and transmitting its patterns to the brain. There are two types, called rods and cones because of their shape. The cones are what give us colour vision, while the rods detect only the intensity of light. Cones just can’t operate in dark situations, which is why in the dark things seem bleached of colour.
The exact workings are still not entirely understood, but retinol is a crucial component of the light sensitive pigment rhodopsin that makes the rods work. It’s also crucial for the cones, but rods seem more sensitive to its loss. If there isn’t enough floating about, the rods don’t work very well, and night vision suffers.
Without retinol you couldn’t see in the dark but more isn’t necessarily better. If you take in more than you need the body just stores the excess in your liver, and dietary deficiency is rare in the west. So don’t start eating carrots by the sack load expecting to develop x-ray vision. Leave that to superman.