Friday, 31 January 2014

Age-related macular degeneration (AMD)

Robert Glass Blog - January 2014

Research has shown that antioxidants in the diet can slow the progression of age-related macular degeneration (AMD). The largest trials which have looked at this relationship are the Age-Related Eye Disease Study’s (AREDS 1 and 2). AREDS 1 (2001) found that people with the intermediate stage of dry AMD reduced their risk of developing advanced AMD (wet AMD) by 25% with a supplement which contained antioxidant vitamins. The AREDS 2 trial has now confirmed an improved version of this formula.

Visiting the optometrist can help identify the early and intermediate changes to your macula allowing you to make early treatment choices. Your visit may require drops to dilate your pupils so please make arrangement not to drive when attending and for approximately three hours afterwards.

Antioxidants are mainly found in fruits and vegetables and protect the body against damaging molecules known as free radicals. 
Free radicals are produced in the body when oxygen reacts with other molecules. They are known to damage or destroy cells, altering their function and preventing them from regenerating.

They may be formed in the retina (the light sensitive area at the back of the eye which contains the macula) due to its high demand for oxygen. Long term exposure may cause damage of the light sensing cells responsible for vision. Due to their potential to combat free radicals, diets rich in antioxidants have become of popular interest in the protection of AMD.

In the AREDS 1 study, research on antioxidants and eye health has mainly been focused on the vitamins A, C, E and zinc. The supplement in AREDS 1 contained: zinc – 80mg, vitamin C – 500mg, vitamin E – 400IU, copper – 2mg and beta-carotene – 15mg. A small amount of copper was added to the supplement as high doses of zinc can reduce the level of copper in the body.

Safety of AREDS 1 components
AREDS 1 showed that 7.5% of patients had an increased risk of hospital admission due to bladder/kidney complications from the high doses of zinc. Other research has found that smokers who take high doses of beta-carotene, as found in the AREDS 1 supplement, may be at an increased risk of developing lung cancer. In people with heart disease or diabetes taking high dose vitamin E supplements may increase their risk of heart failure.

The AREDS 2 trial (2008 – 2013) tested omega-3 as well as lutein and zeaxanthin as additional ingredients to the earlier AREDS formula. It also tested whether reducing the amount of zinc or taking out beta-carotene would reduce the numbers of reported side effects and still have the same benefits of reducing the risk of progression to advanced AMD.
It found that overall, there was no additional benefit of adding omega-3 fatty acids or lutein and zeaxanthin to the original formula, however, participants who took a version of the AREDS formula which contained lutein and zeaxanthin instead of beta-carotene, had their risk of progression to advanced AMD reduced by 18%.
Participants who had a low dietary intake of lutein and zeaxanthin at the start of the study who took a version of the AREDS formula with lutein and zeaxanthin instead of beta-carotene were also 25% less likely to develop advanced AMD.

Lowering the amount of zinc from 80 mg to 25mg and removing beta carotene from the original formula did not reduce the effectiveness of the supplements in protecting against the development of advanced AMD.
Beta-carotene appeared to increase the risk of lung cancer in previous smokers so it is likely to be safer for anybody who has ever smoked not to take supplements that contain beta-carotene. The lowered amount of zinc is also very likely to result in fewer stomach upsets in people taking the supplement.

The investigators now suggest that beta-carotene should be removed from the original AREDS formula and replaced with lutein and zeaxanthin. The recommended doses for this formula based on AREDS 1 and 2 are: Vitamin C 500mg, Vitamin E 400IU, Lutein 10mg, Zeaxanthin 2mg, Zinc 25mg, Copper 2mg.
Other trials which have investigated antioxidants in the progression of AMD have found similar results to AREDS 1 and 2 but are of lower quality and reliability.
AREDS 1 and 2 do not provide enough evidence to show that taking the supplement will prevent the onset of AMD.

Thanks to the Macular society for providing this information.