Degeneration of the central portion of the retina can lead to poor vision and blindness, a disease known as age-related macular degeneration (ARMD). Millions of people in the U.S. are afflicted with this vision degeneration. Harvard Medical School researchers published the twins study in the July 2006 edition of Archives of Ophthalmology regarding age-related macular degeneration.
Researchers studied genetic and environmental risk factors for development of ARMD in a large group of elderly male twins who had served in the United States armed forces. The study included 681 twins; 222 twins suffered with AMD either of an intermediate or late stage, whereas 459 sets of twins did not have any evidence of the condition.
Researchers found that smokers had a 1.9-fold increased risk of developing degeneration of the eye, where past smokers had an approximately 1.7-fold increased risk.
Increased intake of fish reduced the risk of vision degeneration, particularly for those who ate two or more servings of per week. Dietary omega-3 fatty acid intake was inversely associated with this poor vision, reducing risk by about 45%. The authors concluded that this study of twins provided further evidence that cigarette smoking increased the risk, while fish consumption and omega-3 fatty acid intake from fish oil and krill oil reduced the risk, of loss of vision. This protective effect was wiped out however, in people who also had a high dietary intake of omega-6 fatty acids or linoleic acid. Linoleic acid is found in foods containing vegetable oils, such as margarine, corn and safflower oil, salad dressing and baked and processed foods.
So, if you are at risk for AMD, you should not limit your fat intake. You should increase your intake of omega-3 fatty acids and decrease your intake of omega-6. The ideal ratio of omega-6 to omega 3 is 2:1, not the 20:1 or even 50:1 ratio found in some American diets. That means you should eat more fish, omega-3 fish oils including krill oil, walnuts, flaxseeds and tofu. Eat less processed foods, trans-fats, and foods containing vegetable oils. The best oils to use are olive and coconut oil. The worst oils are corn, peanut, safflower, and sunflower.
Seddon JM, George S, Rosner B. Cigarette smoking, fish consumption, omega-3 fatty acid intake, and associations with age-related macular degeneration: the US Twin Study of Age-Related Macular Degeneration. Arch Ophthalmol. 2006 Jul;124(7):995-1001.