Age-related macular degenerationmacular degeneration (AMD) -- the leading cause of age-related vision loss -- is nearly twice as common in elderly smokers as nonsmokers. And seniors who eat fish at least twice weekly are almost half as likely to have AMD than those who eat fish less than once a week.
So say Johanna Seddon, MD, and colleagues in July's Archives of Ophthalmology. Seddon works at the Massachusetts Eye and Ear Infirmary, which is affiliated with Harvard Medical School in Boston.
Halfway around the world in Australia, other experts found that age-related macular problems are rarer in people whose diets are rich in omega-3 fatty acids, which are found in fish, including salmon and mackerel, as well as flax seeds and walnuts.
Seddon's team studied data from 681 individual male twins in their mid-70s who were World War II veterans. The group included 222 men with intermediate- or late-stage AMD and 459 with early or no AMD.
"Current smokers had a 1.9-fold increased risk of AMD while past smokers had about a 1.7-fold increased risk" of AMD, compared with nonsmokers, the researchers write.
The study also shows that men with the highest fish consumption (at least two weekly servings) were 45% less likely to have AMD than those with the lowest fish consumption (less than one weekly serving).
The Australian researchers included Brian Chua, BSc, MBBS, MPH, of the University of Sydney's ophthalmology department.
Chua and colleagues studied nearly 2,900 people aged 49 and older (average age: 63-65 years). Participants completed dietary questionnaires; five years later, they got special photographs of their retinas to screen for AMD.
Participants who reported eating at least one weekly serving of fish were 40% less likely to develop early-stage AMD during the study, compared with those who reported eating fish less than once a month or not at all.
People who ate fish frequently were also less likely to have late-stage AMD, the study shows. But that pattern was only seen in participants who reported eating fish at least three times weekly.
Fatty Acid Balance
When it comes to reducing AMD risk, striking the right fatty acid balance might be important, note Seddon and colleagues.
In their study, the reduced AMD risk was mainly seen in people who consumed high levels of omega-3 fatty acids and low levels of an omega-6 fatty acid called linoleic acid, which is found in vegetable oils including corn, safflower, and sunflower.
Seddon and colleagues aren't against omega-6 fatty acids. But they note that a lot of people consume way too much omega-6 fatty acids, compared with omega-3 fatty acids.
"The ideal omega-6/omega-3 ratio is 3:1 to 4:1," Seddon's team writes.
"However, the average American's diet has an omega-6/omega-3 ratio that ranges from 10:1 to 50:1 ... Our results suggest that when our diet is rich in these omega-6 fatty acids (as measured here by linoleic acid), the protective effect of omega-3 fatty acids is dampened."
Chua's Australian study couldn't confirm those results.
The studies don't prove that not smoking or eating fish prevented AMD.
Both studies were purely observational; participants weren't asked to quit smokingquit smoking or change their diets. The studies also don't specify what type of fish participants ate, or how the fish was prepared.
Still, the results held after adjusting for other AMD risk factors.
Inflammation might partly explain the results, the researchers note. They point out that smoking boosts inflammation, while omega-3 fats reduce inflammation.