Older adults who eat fatty fish at least once a week may have a lower risk of serious vision loss from age-related macular degeneration, a new study suggests.
The findings, reported in the journal Ophthalmology, do not prove that eating fish cuts the risk of developing the advanced stages of age-related macular degeneration, or AMD.
But they add to evidence from previous studies showing that fish eaters tend to have lower rates of AMD than people who infrequently eat fish.
They also support the theory that omega-3 fatty acids -- found most abundantly in oily fish like salmon, mackerel and albacore tuna -- may affect the development or progression of AMD.
AMD is caused by abnormal blood vessel growth behind the retina or breakdown of light-sensitive cells within the retina itself -- both of which can cause serious vision impairment. AMD is the leading cause of blindness in older adults.
There is no cure for AMD, but certain treatments may prevent or delay serious vision loss.
A U.S. government clinical trial found that a specific high-dose mix of antioxidants -- vitamins C and E, beta- carotene and zinc -- can slow the progression of AMD that is in the intermediate stages, and doctors now commonly prescribe it for such patients.
Whether fish or omega-3 supplements can stall AMD progression is not yet clear. But a follow-up to the U.S. antioxidant trial is now looking at whether adding fish oil and the antioxidants lutein and zeaxanthin to the original supplement regimen brings additional benefits.
For the current study, Bonnielin K. Swenor and colleagues at Johns Hopkins University in Baltimore analyzed data from 2,520 adults aged 65 to 84 who underwent eye exams and completed detailed dietary questionnaires.
Fifteen percent were found to have early- or intermediate-stage AMD, while just under 3 percent were in the advanced stage of the disease.
Overall, Swenor's team found, there was no clear relationship between participants' reported fish intake and the risk of AMD. However, there was a connection between higher intake of omega-3-rich fish and the odds of advanced AMD.
Study participants who ate one or more servings of such fish each week were 60 percent less likely to have advanced AMD than those who averaged less than a serving per week.
That was with factors like sex, race and smoking habits -- which have been linked to AMD risk -- taken into account; women appear to be at greater risk of AMD than men, while whites are at greater risk than African Americans and smokers face a higher risk than non-smokers.
Still, the findings do not prove that omega-3-rich fish bestowed the benefit.
"While the current research indicates that a diet rich in omega-3 fatty acids can reduce the risk of late AMD in some patients, more research is still necessary," Swenor told Reuters Health in an email.
She pointed out that this study was "cross-sectional" -- meaning it assessed participants at one time point, rather than following them over time to see whether self-reported fish eaters were less likely to develop AMD. So it is not clear whether participants' reported diet habits preceded the development of the eye disease.
The study also relied on people to accurately recall and report their typical eating patterns, which is subject to error.
Nor is it clear, Swenor said, why greater consumption of omega-3-rich fish was related to a lower risk of advanced, but not earlier-stage, AMD.
For now, she suggested that people with AMD discuss all their "dietary options" with their ophthalmologist.
In general, though, eating fish regularly is considered a healthy move. The American Heart Association, for example, recommends that all adults aim to eat fish, preferably fatty varieties, at least twice per week, for the potential benefits for heart health.