Age related macular degeneration (AMD) is the most common cause of blindness in people over the age of 50 in the UK. In March this year I wrote about the links between B vitamins, homocysteine and AMD and in August last year I discussed the links between diet in general and eyesight preservation.
The macular is the light sensitive area in the centre of the retina that controls visual field and the ability to see colours. AMD is caused by the deterioration of the macular. As this happens the peripheral, outer, vision remains intact as the centre field of vision becomes slowly blurry, grey or filled with a large black spot. Two forms of AMD exists: the dry form which develops slowly, accounting for 90% of all cases; and the wet form which causes rapid deterioration of central vision.
The exact causes of AMD are unknown although free radical damage, where unstable oxygen molecules damage the eye cells, is strongly implicated. Tobacco smoke and sun exposure can increase the level of free radicals in the body and both are a risk for AMD. High blood pressure and diabetes are also risk factors as these conditions can limit blood flow to the eyes.
For more information please visit Macular Disease Society website. The Macular Disease Society aims to build confidence and independence for those with central vision impairment. They are the only UK charity dedicated to helping people with macular degeneration and offer information, a helpline, counselling and emotional support among other resources.
Evidence for diet and nutrition in the prevention, and to a certain extent treatment, of the condition is growing yearly. Since free radicals are implicated in the causation and progression of AMD it may be that antioxidant nutrients such as vitamins A, C and E, carotenoids like lutein and zeaxanthin and various phytonutrients and flavonoids, bioactive plant chamicals, are protective. Omega 3 fatty acids may also play a protective role via their anti-inflammatory effects.
This month three studies (1,2,3) have been published linking diet to AMD.
The first study (1) involved 4003 participants in the Age-Related Eye Disease Study (AREDS), there were 7,934 eyes included in the study. Dietary intakes of vitamins C and E, zinc, lutein and zeaxanthin, the long chain omega 3 fatty acids DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), and low-dietary glycaemic index foods were analysed and the association between AMD was evaluated. The results showed that consuming diets that had a low glycaemic index and high intakes of the nutrients listed was associated with a reduced risk of AMD.
A healthy diet rich in a variety of vegetables, fruits, beans/pulses, nuts/seeds, unprocessed meats and fish, especially oily fish, and unprocessed, unrefined wholegrain carbohydrates will provide these nutrients. Lutein and zeaxanthin are plant pigments that are found in broccoli, spinach, green leafy vegetables and egg yolks.
The study(1) also found that diets containing foods with a low glycaemic index, also appeared protective against AMD. Glycaemic index is a measure of how rapidly a food causes blood sugar levels to rise. High-GI foods, like white bread, many processed foods (especially high carbohydrate foods) and potatoes, tend to spur a quick elevation in blood sugar, while low-GI foods, such as lentils, nuts, beans and many high-fibre unrefined grains, create a more gradual increase in blood sugar. The blood-sugar surges associated with high-GI diets may eventually damage the macula. This is probably because consistently high blood sugar levels can damage fats and proteins and may put the body into oxidative stress, which over time damages cells and may lead to various diseases, including AMD.
The other two studies (2,3) looked at the links between dietary fat intake and AMD. In the blog post that I wrote in August last year I discussed many studies that linked a high intake of long chain omega 3 fatty acids, found in oily fish, to a reduced risk of AMD. The first of these two studies (2) found that regularly eating foods rich in healthy fats such as fish, nuts and olive oil is associated with a reduced risk of AMD and the second study (3) has found that avoiding trans fats (often found in baked and processed foods) is also associated with a reduced risk of the condition.
The first report (2) involved 2,454 participants in the Blue Mountains Eye Study, which began in 1992. The individuals involved completed food frequency questionnaires that were used to analyse and determine their intake of various fatty acids. Digital photographs of the retina were used to assess the development of AMD five and ten years later.
Eating one serving of fish per week was associated with a 31% lower risk of developing early AMD. Eating one to two servings of nuts per week was associated with a 35% lower risk of early AMD. It is not known for definite why the fatty acids are protective against AMD but the fats may be protecting the eyes by reducing inflammation, blood vessel formation or oxidative damage in the retina. Omega 3 fatty acids are known to be helpful in reducing inflammatory chemicals in the body (I have previously written a lot about this in various blog posts).
The other report (3) analysed data from 6,734 individuals aged 58-69. During the follow-up period, 2,872 cases of early AMD and 88 cases of late AMD developed. Individuals who consumed higher levels of trans-unsaturated fats-often found in baked goods and processed foods-were more likely to have late AMD. This study also found that individuals who consumed the most omega-three fatty acids were less likely to have early AMD.
Trans-unsaturated fatty acids may be causing damage through their effect on cholesterol levels as well as through their inflammation increasing effects. Trans fats are also linked to an increased risk of heart disease as well as other conditions.
Available ‘eye health’ supplements often contain vitamins C, E, beta carotene and the mineral zinc in addition to lutein and zeaxanthin. The rationale behind this comes from dietary association studies and some research evidence. If you are considering supplements remember that they are not a substitute for nutritious daily meals! A healthy diet, rich in a variety of vegetables and fruits, will provide an array of antioxidant nutrients to keep the whole body healthy, including the eyes. Healthy omega 3 fats from oily fish and nuts/seeds (especially flaxseeds and walnuts) are also a vital part of a balanced diet. Individuals who do not regularly eat oily fish such as salmon, mackerel, sardines or trout (at least twice per week) may consider taking a fish oil supplement to provide 250mg-350mg EPA and 250-350mg DHA per day, vegetarians may consider a flaxseed oil supplement to provide 500-1000mg alpha-linolenic acid per day.
(1) Chung-Jung C et al. 2009. Dietary compound score and risk of age-related macular degeneration in the age-related eye disease study. Ophthalmology. 116:939-946
(2) Tan JSL et al. 2009. Dietary Fatty Acids and the 10-Year Incidence of Age-Related Macular Degeneration. The Blue Mountains Eye Study. Arch Ophthalmol. 127(5):656-665.
(3) Chong EWT et al. 2009. Fat Consumption and Its Association With Age-Related Macular Degeneration. Arch Ophthalmol. 127(5):674-680.
Written by Ani Kowal
Related posts:
- Looking after eyesight, natural protection against Age Related Macular Degeneration (AMD)
- Dietary advice for eyesight preservation
- Studies show that good bacteria in the gut do more than just protect our digestive systems
- Long chain omega 3 fats shown again to be important for eye health
- More evidence suggests that eating oily fish might protect the eyes
