Researchers report that omega-3 fatty acids found in fatty fish such as tuna and salmon could protect against progression of age-related macular degeneration, but the benefits appear to depend on the stage of disease and whether certain supplements are taken.

Age-related macular degeneration is a progressive disease associated with aging that attacks central vision, resulting in a gradual loss of eyesight and, in some cases, blindness. Macular degeneration affects the macula, the part of the eye that allows you to see fine detail. In some cases, macular degeneration advances so slowly that people notice little change in their vision. In others, the disease progresses faster and may lead to a loss of vision in both eyes. The National Eye Institute (NEI) reports that macular degeneration is the most common causes of non-remediable vision loss in Americans over 60.

The researchers calculated intakes of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) from dietary questionnaires administered to 2,924 men and women, aged 55 to 80 years, participating in an eight-year supplement trial, the Age-Related Eye Disease Study (AREDS) of the NEI. The AREDS trial results suggest taking supplements of antioxidants plus zinc prevents progression of late-stage macular degeneration. AREDS study participants were randomly allocated to receive either a placebo or supplements containing the antioxidants vitamins C and E and beta carotene, the minerals zinc and copper, or a combination of both.

“In our study, we observed participants with early stages of macular degeneration in the placebo group benefited from higher intake of DHA, but it appears that the high-dose supplements of the antioxidants and/or the minerals somehow interfered with the benefits of DHA against early macular degeneration progression,” says senior author Allen Taylor.

The antioxidant supplements did not seem to interfere with the protective effects of DHA and EPA against progression to advanced stages of macular degeneration. Participants who consumed higher amounts of DHA and EPA appeared to have lower risk of progression to both wet and dry forms of advanced macular degeneration.

“Data from the present study also shows the supplements and omega-3 fatty acids collaborate with low-dietary glycemic index (dGI) diets against progression to advanced macular degeneration,” says corresponding author Chung-Jung Chiu. “Our previous research suggests a low-GI diet may prevent macular degeneration from progressing to the advanced stage. We hypothesize that the rapid rise of blood glucose initiated by high-GI foods results in cellular damage that retinal cells cannot handle, thus damaging eye tissues.”

dGI is a scale used to determine how quickly carbohydrates are broken down into blood sugar, also known as blood glucose. Foods such as sweetened drinks, sodas and white bread are high-GI because they trigger a sharp rise and fall of blood sugar. Low-GI foods, such as whole grain versions of pasta and bread, have a milder effect on blood sugar response. Earlier data published by Taylor and Chiu suggests that daily substitution of five slices of whole grain bread for white bread out of a total intake of 250 g of carbohydrate might cut out almost 8% of advanced macular degeneration over five years. This is readily achievable with little diet behavior modification.

Eating two to three servings of fatty fish such as salmon, tuna, mackerel, shellfish, and herring every week would achieve the recommended daily intake of DHA and EPA. However, the majority of AREDS participants and Americans eat a much lower level than recommended. “If changing dietary habits is not easy, supplementation is an option,” says Chiu.

The authors stress it is still premature to conclude dietary recommendations for people with macular degeneration and more studies are warranted. “Taken together, these data indicate that consuming a diet with higher levels of omega-3 fatty acids, antioxidants and low-GI foods may delay compromised vision due to macular degeneration,” says Taylor. “The present study adds the possibility that the timing of a dietary intervention as well as the combination of nutrients recommended may be important.”
References:
1. Allen Taylor, et al. Tufts University School of Nutrition via Newswise Medical News.
2. National Eye Institute.