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Which nutrients might help prevent the most common cause of blindness in the elderly?

Posted Sep 16 2008 6:54am

Macular degeneration is the most common cause of blindness in the elderly. And sufferers of this condition in England had some welcome news this week when the barring from use of a drug used to treat this condition (Lucentis) by National Health Service (NHS) doctors was reversed. This means that doctors in the state medical system in England can now prescribe this drug to individuals suffering from one of the two main forms of this condition known as ‘wet’ macular degeneration.

This story reminded me that there are certain nutritional approaches that may have merit in the prevention or treatment of age-related macular degeneration (AMD). One nutritional factor that has caught the eye of scientists in this respect are the omeg-3 fats found in oily fish such as salmon, trout, sardine, mackerel and herring. In a recent study [1], eating oily fish one a week was found to be associated about half the risk of AMD compared to individuals eating less than this. The researchers also looked at the relationship between the intakes of the two main types of omega-3 fat in fish (DHA and EPA) and their relationship with AMD risk. They found:

Those eating the highest amounts DHA were at a 68 per cent reduced risk of AMD

Those eating the highest amounts EPA were at a 71 per cent reduced risk of AMD

Quite recently, a group of scientists reviewed the available evidence regarding the relationship between omega-3 fats and AMD [2]. Their analysis found that a high dietary intake of omega-3 fatty acids was associated with a 38% reduction in the risk of AMD accoutring later in life rather than earlier (late AMD).

Now, even a stack of studies of this nature a mile high would tell us whether omeg-3 fats actually prevent AMD. However, it should be borne in mind that there are a number of mechanisms through which omega-3 fats may have benefit here.

To begin with, a gumming up of the arteries (atherosclerosis) that supply blood to the retina at the back of the eye is thought to contribute to AMD, and the great likelihood is that omega-3 fats help to protect against this process. Also, DHA levels of very high in the retina, and there is some evidence which suggests this nutrient has a key role in the visual process. EPA, through its conversion into substances called eicosanoids may have the ability to combat other eicosanoids of other kinds that have been implicated in the development of AMD through their ability to, say, cause inflammation and leakiness of blood vessels.

Another process that has been implicated in the development of AMD are damaging, destructive molecules known as ‘free radicals’. This has led some to consider whether combating free radicals with nutrients that have antioxidant action might help to prevent or retard AMD. By far the biggest study to test this concept is the Age-Related Eye Disease Study (AREDS) which was published in 2001 [3].

Here, literally thousands of individuals deemed to be at high risk of AMD were treated for an average of more than 6 years with one of the following:

1. The antioxidants vitamin C (500 mg per day), vitamin E (400 IU per day), and beta carotene (15 mg per day)

2. Zinc oxide (80 mg per day) with copper (cupric oxide at a dose of 2 mg per day)

3. The antioxidants plus zinc

4. Placebo

The results were:

The antioxidant combination reduced the risk of developing advanced AMD by 20 per cent.

The antioxidant and zinc combination reduced risk by 28 per cent.

Zinc alone reduced risk by 25 per cent.

Now, the group responsible for this research have embarked on a new study to test the effectiveness of other nutritional approaches in eye disease (AREDS II). They will be testing the effects of two so-called ‘carotenoid’ nutrients – lutein and zeaxanthin – that studies have found to be linked with a reduced risk of AMD. The lutein and zeaxanthin are to be combined with another promising nutrient in the prevention of AMD – you guessed it: omega-3 oils.

References:

1. Augood C, et al. Oily fish consumption, dietary docosahexaenoic acid and eicosapentaenoic acid intakes, and associations with neovascular age-related macular degeneration. Am J Clin Nutr. 2008;88(2):398-406

2. Chong EW, et al. Dietary omega-3 fatty acid and fish intake in the primary prevention of age-related macular degeneration: a systematic review and meta-analysis. Arch Ophthalmol. 2008;126(6):826-33

3. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol. 2001;119(10):1417-36.

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