I was never very interested in food as a child, but I do remember being encouraged to eat plenty of carrots to help me see in the dark. Not all nutritional folklore is supported by sound science, but this one is: carrots are loaded with the nutrient betacarotene, and the vitamin A this may convert to in the body is indeed important for night vision. In recent years, however, science has begun to examine more closely the link between diet and eyesight. In particular, researchers have been busy identifying the true causes of deteriorating eyesight, in an attempt to discover ways of protecting against eye disease. It turns out that the humble carrot, in addition to helping with night sight, has other ocular benefits up its sleeve. The latest research suggests that consuming carrots and other deeply coloured vegetables may do much to preserve our visual powers as we age.

Much of the scientific community's recent research into the links between diet and eye health has focused on a condition known as macular degeneration. The macula is part of the retina, the structure at the back of the eye that essentially fulfils the same function as film in a camera. The macula 'sees' whatever our eye is focusing on, and is responsible for our most detailed and intricate vision. However, as with all the other parts of our body, the macula can be subject to the vagaries of time. Damage to the macular as we age can give rise to a condition known as age-related macular degeneration (AMD). AMD tends to be one of those conditions you don't hear about until you have it. Yet despite its relative obscurity, it is actually the most common cause of visual deterioration and blindness in the developed world.

For a long time, AMD has been viewed as a natural part of the ageing process, and a condition about which we could do very little. However, a better understanding of what actually causes AMD has thrown up some very promising possibilities for its treatment and prevention. In recent years, scientists have discovered that AMD is related to molecules known as free radicals. Free radicals are natural by-products of the biochemical and physiological processes that keep us alive. Essentially waste products, free radicals are believed to be the major players in the damage characteristic of AMD. However, these rogue molecules don't get it all their own way in the body. The effects of free radicals are tempered by substances known as antioxidants, many of which are nutrients. The good news is that upping our intake of antioxidants appears to help protect against AMD.

The antioxidants that appear to offer most potential in this respect are a class of compounds known as the carotenoids. The most famous of the carotenoids is betacarotene. However, its relatives lutein and zeaxanthin also seem to protect the eyes from free radical attack. Carotenoids are found in dark-green and orange-yellow vegetables, such as spinach, broccoli, squash, and of course, carrots. Not surprisingly, more than one study has found that high levels of carotenoids in the system appear to protect against AMD. It appears that eating plenty of carrots and other carotenoid-rich veggies is a worthwhile insurance policy against visual problems later in life.

Our diet offers more potential for the preservation of our eyesight in the form of wine. One study published recently found that as little as two to 12 glasses of red or white wine per year might reduce the risk of AMD by up to a half. While it is not known for sure what the protective factor is, wine is known to contain substances called flavonoids that do have antioxidant action in the body. Although very moderate wine consumption appears to be beneficial, it is not known whether more is better. Nevertheless, it does seem likely that the occasional glass of wine has benefits for our eyes.

While the right diet might offer real potential for protecting against AMD, I generally recommend a more aggressive approach for individuals who already have signs of this condition. Supplements of eye-supporting nutrients may provide benefits in addition to those provided by dietary change. In fact, a study published last year found that taking a supplement containing betacarotene and other antioxidants (vitamins C and E) significantly reduces the risk of severe AMD in those who might be highly susceptible to this condition. For those interested in affording themselves the best protection, I usually recommend a supplement called OcuPlus. This has been specifically formulated with macular degeneration in mind, and contains a complex of all the nutrients associated with a reduced risk of AMD. OcuPlus is available by mail order on 020 8785 3730.

Dear John...

About eight years ago I had an operation for varicose veins in my left leg. Last year I started to develop blood clots in my left thigh, around the area where the vein had been stripped. The pain these clots cause has been helped by the ibuprofen my doctor prescribed. Is there a more natural alternative to reduce the inflammation that seems to cause the clots?
Veena Arnold, Bath

It sounds to me as though you are suffering from thrombophlebitis. This is characterised by inflammation and blood-clot formation in a vein near the skin's surface. Typical symptoms include swelling, redness and tenderness in and around the affected area. Conventional treatment is based on the use of support stockings, bandaging and the administration of non-steroidal anti-inflammatory drugs, such as Ibuprofen.

A major component of the tiny blood clots that occur in thrombophlebitis is a blood protein called fibrin. The body breaks down fibrin naturally in time, but certain foods, such as garlic, onions, cayenne pepper and ginger, have the ability to accelerate this process. I suggest you include plenty of these foods in your diet. One natural substance that may be of real benefit to you is bromelain. This extract of pineapple has been shown to break down fibrin and therefore acts as a natural clot dissolver and blood thinner. It also has anti-inflammatory actions in the body and might help to reduce the pain and swelling in and around the vein.

Nutrition news: Cod philosophy

Cod-liver oil has long been fabled for its ability to ease joint aches and pain. Now it appears that cod-liver oil might also be a useful supplement to take during pregnancy. A study has shown that the children of pregnant women who took cod-liver oil are 70 per cent less likely to develop diabetes. Another potential advantage is that cod-liver oil is rich in docosahexaenoic acid (DHA), a healthy fat that is believed to be crucial to early brain development. However, cod-liver oil needs to be handled with a modicum of care, as it contains vitamin A, the upper limit of which is 10,000 IU each day during pregnancy. But as 1 tsp of cod-liver oil contains only about 2,500 IU of vitamin A, taking a daily capsule or two during pregnancy is pretty much risk free.

· If you have any issues you would like Dr John Briffa to address in this column, please contact him by email on life@observer.co.uk. Please note that Dr Briffa cannot enter into any personal correspondence.