The eyes are not just a window to the soul; they may be a surprisingly reliable guide to how healthily you eat. While there is no correlation between refusing to eat your carrots and actual night vision, nutrition and optical health are closely linked, with scientists currently looking at the role played by vitamins and minerals in the prevention of eye diseases, such as age-related macular degeneration (AMD) and cataracts.
That a link exists has long been understood: the eye condition xerophthalmia, a common cause of blindness in developing countries, is known to be caused by a lack of vitamin A, which is found in sources such as meat and fresh vegetables.
In fact, vitamins and minerals are crucial to eye health, as they are constantly required to help ward off damage caused by UV light rays. A healthy blood supply is necessary to supply nutrients and oxygen to the eye. So, conditions such as high cholesterol, which clog arteries elsewhere in the body, are also important in the eye region.
Professor Ian Grierson, head of ophthalmology at the University of Liverpool, is one of the pioneers in nutritional research. He says: “It is quite difficult to show real benefit to an individual, that by changing their diet it will benefit their sight – the studies needed would be too big and expensive.”
However, Prof Grierson approaches the idea from a different angle: “My interest is in AMD. For a lot of sufferers of this condition, there are no treatments at all, so it occurred to me to look at the risk factors for the disease instead, with a view to prevention.
“These risk factors don’t just make you more prone to developing AMD, but to it becoming more severe if you do have it.”
He explains: “AMD is on the march as we are all living longer [according to the Macular Disease Society, AMD affects 30 million people worldwide, half a million of them in the UK], and it is undoubtedly lifestyle related.
“The main risk factors are gender (females are more susceptible), your age (the older you are, the more likely you are to develop it), whether you smoke or have done, your weight, and your diet.”
Problems occur because the macula (the centre of the retina) works so hard to give us colour and fine vision, it also produces by-products called free radicals that damage the cells. Prof Grierson explains: “It is like a factory in there. The antioxidants which we get from food protect our cells from these toxins by neutralising them, but if the diet is deficient in the right ones there is no safety net, and the macula suffers permanent damage.
“We really need to increase levels of the right antioxidants in patients and the general population.”
So, which are the nutrients that we need to top up our diets with? According to Prof Grierson, while research suggests that vitamins A, C, E and zinc can help keep the eye healthy, it is carotenoids, the pigments that occur naturally in plants and algae, which offer the most precise way of targeting the damage that causes sight loss.
In particular, the carotenoids lutein and zeaxanthin seem to act directly to absorb damaging blue and near-ultraviolet light, in order to protect the macula. “I call them the macula’s sunglasses,” says Prof Grierson. “Any plant or vegetable which is yellow or orange in colour contains them.” They are also found in abundance in green vegetables such as kale and spinach.
We should be eating 6mg of lutein a day, but the average consumption is 2mg. “That’s way too low,” says the professor. “In the Second World War, our average intake was 4-5mg and we weren’t even trying.”
But you can’t just eat vegetables alone: the lutein needs fat to be absorbed, so you are allowed a little butter on your garden peas. In fact, a 2005 study at the Ohio State University, Columbus, found that carotenoids absorption was enhanced by the consumption of avocado oil and fruit.
So, should you take one of the many supplements on the market to help maintain healthy eyes? Prof Grierson says: “I’d prefer that you thought about diet and then take a supplement rather than jump straight to the tablet. But when I go to the US on lecture tours, I know I won’t eat as healthily as at home, so I take a supplement with me to make sure. Even if you have a good diet, there will be times when you can’t eat perfectly or won’t have control over your diet.”
And, if you choose a supplement, “Use your common sense,” he advises. “Creating a vitamin supplement is an expensive business, so don’t look for or expect a bargain. Find one that gives you 6mg of lutein a day.”
Other nutrients have been found to be potentially beneficial, such as the red pigment lycopene (found in fresh tomatoes, tomato sauces and water melons), which has shown promise in studies on the prevention of prostate cancer.
Omega-3 and omega-6 essential fatty acids are also good for maintaining eye health, says ophthalmologist David Allamby of Focus Laser Eye Clinic in London (www.focusclinics.com). “Tear film has a layer of oil which helps keep water on the surface of the eye. If you are deficient in omega-3s, you may suffer dry, uncomfortable eyes.”
Essential fatty acids can be found in flax seed (milled organic flaxseed, 425g, £7.50; www.linwoods.co.uk), nuts, pulses and oily fish.
Nutritionist Ian Marber adds: “Night vision may be improved with vitamin A found in fresh fruits and vegetables as they contain a variety of carotenoids, but supplements may not be necessary. There is some evidence that suggests that vitamin A supplementation can increase the risk of some forms of cancer, and so getting it from food is advisable.”
If you do want to get more vegetables into your diet, greengrocer and author Gregg Wallace, co-presenter of BBC1’s Masterchef, suggests you always buy as fresh as possible, and try to keep nutrients and taste intact. “Remember this is or was a living thing; don’t stick it in the fridge, keep it in the sunshine.”
When you’re cooking, “Don’t over-peel veg,” he advises. “In root vegetables, such as carrots, the nutrients are just under the skin, so just give them a gentle scrape.”
Potatoes should be cooked in their skins to preserve nutrients, “otherwise all the vitamins just leach into the cooking water which you throw away. Peel them afterwards using a tea towel to hold them.”
He points out that frozen veg is not disastrous, either, as it is often frozen so fast after picking. But he says that we should try to eat seasonally (bar fruit and veg which won’t grow here, such as bananas) if possible. “At the moment I’m eating lots of pears (I love the honeyed juice) and brassicas, such as cabbage and kale. I can feel them doing me good.”
Prof Grierson, who has written a cookbook, Vegetables for Vision: Nature’s Supplements for Eye Health (£14.50, www.waterstones.com), suggests we aim for a “brightly coloured plate, a ‘traffic lights’ of vegetables” to be sure of getting enough nutrients, and not to worry if they are a bit old, as carotenoids last longer than vitamins.
He is, however, not suggesting that eating up your greens, yellows and reds is the ultimate panacea for blindness. “I cannot guarantee that this will work for everyone. Some patients will address every risk factor and still get AMD; others defy the logic and never get it. But in a group of 100, 30 will benefit a lot, 40 will benefit a bit, and 30 won’t benefit at all – so the majority will get some value from eating like this.
“The beauty is that it doesn’t require radical change – have a juice with breakfast and some berries on your cereals, add salad to a sandwich at lunchtime, and eat two types of vegetable at dinner.” Gregg Wallace agrees: “You can’t change your diet overnight; just up the portion size gradually.”
And to help you maintain healthy eyes, Prof Grierson says: “Take a one-a-day supplement with a broad base of antioxidants. Happily, your overall health should be maintained, too.”
Don’t forget your eye test
Everyone should take an eye test at least every two years, says London-based ophthalmologist David Allamby, and not just to watch for changes in their prescription.
“We need to check for glaucoma, an eye disease in which the optic nerve suffers damage, caused by increased pressure of the fluid in the eye. it is often called a ‘silent’ disease, as it can cause permanent damage to your sight before you realise anything is wrong.
“With other blinding conditions, such as macular disease (when the cells in the retina degenerate causing loss of vision) or cataracts (clouding of the lens), you will probably notice a difference yourself, but the sooner you come in, the better.
“With cataracts, we can operate to remove them; and even with macular degeneration, we may be able to prevent spread (in some cases), and give you advice on how to cope.
“if you are concerned about changes to your vision, we can advise on surgery or lenses. short sight tends to develop in the teens or 20s; and long sight in middle age — 40s-60s — when you’ll need reading glasses.
“New laser techniques, such as Z-Lasik, can help even that group, and offer ‘blended’ vision, which may leave you seeing better than ever before.”