So this year for Christmas my Mum bought me this hilarious coaster (thanks Mum, love you).
As I am indeed my mother’s daughter the innate stubbornness within me immediately rebels against such a statement, however on today’s topic I will have to give her (and most other parents out there) their dues, carrots really do help you see in the dark. And with that let our voyage into the mystical world of Vitamin A begin (not sure where the fantasy aspect will come in but I’ll give it a go).
So firstly a few little bits of housekeeping.
Vitamin A is a fat soluble vitamin which is highly relevant because it influences the absorption, utilisation and storage of Vitamin A within the body. Fat soluble (as opposed to others which are water soluble) means uptake from food is via a fat based molecule called a chylomicron. This great little globule carries Vitamin A through the lymphatic system of the small intestines and on into general circulation where it is then used or stored. The ability for fat soluble vitamins to persist in the tissues is both a good thing; it means we can accumulate levels within the body to call upon when our dietary intake falls below our requirement, and a bad thing as it opens up the potential for a state known as hypervitaminosis (literally too much of that vitamin present in the body).
Individuals with compromised fat absorption or deficient dietary intake may also find themselves in the opposite camp where their consumption or ability to harness these micronutrients is insufficient to meet their needs. Such a situation can be equally as damaging as vitamins are vital cofactors for many metabolic processes.
Right so we’ve sorted out how we get our A into the body, now onto what we do with it.
Just to muddy the waters ever so slightly Vitamin A actually refers to a number of different but related nutrients that are subdivided into two main categories; provitamin A Retinols and previtamin A Carotenoids (heard of beta carotene? Ahhh and thus the clouds begin to part). So what’s the difference?
First of all where you find them. Retinols are from animal sources whereas as Carotenoids are plant derived. Then there is their availability to our bodies. Retinols can be readily utilised and are the form that we store our Vitamin A in, whereas Carotenoids must be converted to Retinol before their power can be harnessed. If you are in perfect health this is not usually a problem however certain factors such as genetics, digestive issues, alcohol, medications and conditions affecting fat absorption (Crohn’s disease, gallbladder issues and cystic fibrosis to name a few) can depress your bodies ability to perform this conversion.
What on Earth has all of this got to do with our favourite Loony Tunes character you ask? Why is she leading us down this convoluted path after peaking our interest by implying entertainment in her title? Never fear all will now become clear (hopefully).
So we have our Retinol, which we have gained by consuming delicacies such as beef liver, egg yolk, whole milk, butter and fish roe. This has travelled through our digestive system, jumped aboard a chylomicron and is now wending its way through our circulation. Retinol in this primary form is directly responsible for the health of our retinas (scientists really push the creativity boat out with their naming sometimes…). Eye health check number 1.
Then comes number 2. Retinol can then be oxidised to another form known as Retinal (and so the related nutrients from earlier start to appear). Retinal bobs along arms outstretched looking for his love Opsin (a protein), he’s sure that they were supposed to meet today…..luckily they find each other, go in for a big hug and decide to never leave each others sides again. Off they wander into the sunset as the freshest new couple on the block Mr & Mrs Rhodopsin. OK so the married bit might be a tad on the made up side but Retinal and Opsin do indeed bind together to form Rhodopsin, also known as visual purple. This pigment is found in specific cells of the retina known as rods which are responsible for the shades of grey (life’s never black and white) component of our vision. When light hits Rhodopsin it converts it to the electrical signals that travel along the optic nerve to our brains to be interpreted as images. Rhodopsin is so sensitive to light that it is triggered even in the dimmest of settings. Et voila, we can see in the dark. And thus our quest is concluded and we can all go home? Not quite.
So I mentioned before that Retinols are all from animal sources so how do we get from our buddy Bugs’ favourite snack to not walking into things when the lights are off?
Before we start a quick update on Carotenoids. They are a group of plant pigments responsible for the array of bright red, yellow and orange beauties that bejewel a greengrocers display. I’m sure it won’t come as a surprise that carrots are right up there on the list of sources but they are actually pipped to the post by sweet potatoes. Winter squashes, pumpkin, mangoes, kale, spinach, swiss chard and romaine lettuce also land themselves spots up at the top.
Not to be outdone by the Retinols that have gone before them, the Carotenoid group must then be subdivided into Carotenes and Xanthophylls. At this point I think it’s probably unnecessary to delve any deeper into the chemistry of this classification (and there are more than 600 types of carotenoids so we’d be here all day!) let’s continue on instead.
Here’s the important bit, the carotenes (alpha and beta carotene along with beta-cryptoxanthin) are our provitamin A Carotenoids, they are the ones that we can convert into Retinols to go on to become Rhodopsin. Earlier I mentioned that this conversion may be compromised in certain individuals which is true but is not of grave concern to the general public who will gain sufficient levels from animal sources. Therefore they would suffer no ill consequences if their carotenes remain as they are and perform many of their other fantastic functions rather than becoming Retinol. If however you are a vegetarian, vegan, following an extremely low fat diet or have one of the conditions mentioned way back at the beginning it may be a good idea to consider a supplement. This should be done under the guidance of a qualified practitioner however as hypervitaminosis A is not something to be scoffed at.
So you’re saying that carrots really aren’t that important for our eyes and actually we should scrap them and just eat omelettes? Oh noooo now we come on to the Xanthophylls (fun things to try and spell repeatedly..!).
Now these are the big boys when it comes to our eyes.
Lutein and Zeaxanthin are the carotenoids found in the retina and they accumulate at a point called the Macula Lutea. This area directly at the back of the eye is responsible for our sharp, detailed central vision and I think you’ll agree thats a pretty big deal. These two compounds protect this vital part of our eye from blue light which can cause ionisation and retinal damage.
Recent advances in ophthalmology have discovered that supplementing with Lutein and Zeaxanthin is effective in cases of Age Related Macular Degeneration (AMD), a leading cause of blindness. They do this by reducing lens opacity and light sensitivity. The fact that the carotenoids are also hugely potent antioxidants contributes to their eye preserving powers by reducing oxidative stress. This causes damage to the retina as oxidised species are not completely eliminated and accumulate on photoreceptors (specialised cells of the retina that convert light to electrical signals) which is one of the first signs of this condition. By preventing this process and filtering the damaging blue light these troopers literally save our sight. Want a bit more explanation on oxidative stress? Click here to head on over to my post ‘My Heart Beats for Banana Bread’ to find out more.
So the moral of the story? Munching away on carrots (or sweet potato-mango-kale smoothies) may not help you in a blackout (sorry Mum) but reading that tiny font at the bottom of the page when you’re 95? They’ve got you covered.