Getting enough vitamin A is important for healthy eyes. And carrots are a rich and natural source of this vitamin, which is basically a group of chemicals made up of retinal (the active form of vitamin A) and carotenes such as beta-carotene (which gives carrots their distinctive colour).
But a diet overloaded with carrots – and vitamin A – won’t leave you with healthier eyes.
To understand where vitamin A fits in, I’ll first explain a little about the process of vision. When we look at something, light from that object enters the eye and is focused onto the inside back surface of the eyeball, which is lined by a thin layer of cells. This is called the retina.
The retina is responsible for catching light and turning this into a neural signal, which is then sent up to the brain for further processing. In order to perform this wondrous action, the retina has specialised cells, called photoreceptors, each of which is packed with light-catching pigments.
The predominant pigment in the retina is rhodopsin, a major part of which is retinal (vitamin A). When the retinal reacts with light, it induces a cascade of biochemical events and shape changes in the rhodopsin molecule. In turn, this creates an electrical signal. This whole process is known as phototransduction, and this is really where vision begins.
Humans are unable to synthesise vitamin A afresh and, therefore, must take it in through their diet to maintain normal visual function. Vitamin A can be found in a range of meats and vegetables – the most notable being the carrot, though the best source is probably liver.
For most people living in developed countries, adequate vitamin A intake is not an issue, so eating more carrots will make no noticeable difference. This is because our diets contain enough vitamin A and we are able to store it, unlike other nutrients, such as vitamin B.
In fact, well-nourished pregnant women should avoid supplementing their diet with vitamin A when their total daily intake is around 3,000 IU because too much vitamin A (well above 10,000 IU per day) can cause birth defects. But vitamin A-rich foods are safe so you can still munch on a bag of carrots without doing any harm (provided you don’t mind your skin turning orange from the carotenes!).
In the developing world, however, an estimated half a million children become blind each year as a consequence of dietary vitamin A deficiency. But carrots aren’t the answer, as they are not easily grown and don’t last long enough to be distributed. World food programs are instead trialling vitamin A-rich bananas and sweet potatoes as a source of nutrition to improve eye health.
While there is still much to be done to prevent vitamin A deficiency in the developing world, to those reading this article, carrots will make very little difference to your eyesight.