AREDS Reports Numbers 20 and 22

Dietary data was collected from participants when they enrolled in the AREDS trial so that investigators could later examine the relationship of AMD case groups with intake levels of individual nutrients.

To explore these relationships, AREDS subjects were divided into four groups based on increasing severity of drusen or type of AMD. The dietary information from those four groups was then compared with that from AREDS participants categorized as being 'free' of AMD. AMD-free was defined as having no drusen or less than 15 small drusen. Nutrient intake values were adjusted for energy intake then stratified into quintiles.

Results of the analyses were published in the May and September issues of the journal Archives of Ophthalmology. The first of these case-control studies reports on the relationship of dietary lipids and AMD (1), while the second study assessed whether nutrients such as carotenoids, vitamins A, C and E and others, were related to AMD risk (2).

Omega-3 and Fish Intake Lower AMD Risk

The researchers found that only higher intake of total long chain omega-3 and fish (the primary dietary source of EPA and DHA), were linked to a decreased likelihood of having neovascular AMD. Benefit was not seen for the other AMD groups.

Arachidonic acid was the only dietary lipid directly associated with neovascular AMD prevalence. Participants getting the most arachidonic acid in their diets were 54% more likely to have late AMD. Arachidonic acid, an omega-6 fat abundant in meat and dairy, is a precursor for inflammatory eicosinoids.

No statistically significant relationships were seen for other dietary lipids such as the monounsaturates, found in olive oil for example, or saturated fats.

It's interesting to note that the omega-3 fat alpha-linolenic acid, found in flaxseed oil for example, was associated with decreased AMD risk only when it was included along with EPA and DHA as part of the total intake of long chain polyunsaturated fats. Assessed alone, alpha-linolenic was not related to AMD. Alpha-linolenic acid must first be metabolized to EPA to provide anti-inflammatory activity, and this conversion is only 10-20% effective.

Comparing the highest to lowest quintiles, those consuming the most total omega-3 fats were about 39% less likely to have neovascular AMD. Risk reduction for greater fish intake was the same. A 46% lower chance of having late AMD was linked with the highest consumption of DHA.

EPA, DHA and arachidonic acid are major fatty acids in the diet. Both arachidonic acid and DHA (which can be formed from EPA), are key components of retinal photoreceptor outer segments and vascular tissue. While all three of these lipids are essential, a better balance of EPA and DHA to arachidonic acid is recommended for cardiovascular health. This study strongly suggests that improving that balance can favorably influence retinal health as well.

Only Lutein / Zeaxanthin Independently Linked to AMD

Higher dietary intake of lutein and zeaxanthin was independently associated with a reduced likelihood of having neovascular AMD, geographic atrophy, and large or extensive intermediate drusen. No other nutrients were independently related to AMD.

After adjusting for total energy intake and other non-nutritional risk factors, subjects consuming the highest amount of lutein and zeaxanthin were 35% less likely to have neovascular AMD and 55% less likely to have geographic atrophy than those eating the least. Those whose diets provided the most of these two carotenoids also had a 26% reduced likelihood of having large or extensive drusen.

The findings from both of these AREDS case-control studies are, in part, the basis for testing 10 mg of lutein, 2 mg of zeaxanthin, 650 mg EPA and 350 mg of DHA in the AREDS 2 trial currently underway.

References

1. AREDS Report No. 20: The relationship of dietary lipid intake and age-related macular degeneration in a case-control study. Arch Ophthalmol 125:671-9, 2007.
2. AREDS Report No. 22: The relationship of dietary carotenoids with age-related macular degeneration in a case-control study. Arch Ophthalmol 125:1225-32, 2007.