Seniors whose diets are rich in omega-3 fatty acids found in oily fish and fish oil supplements could reduce their risk of age-related macular degeneration (AMD) by up to 70% say U.S. and Australian researchers.

Macular degeneration affects over 30 million people worldwide, and is the leading cause of blindness in people over 50.

People who ate fish at least twice weekly were 45% less likely to have AMD than those who ate fish less than once a week according to Johanna Seddon, M.D. and colleagues at the Massachusetts Eye and Ear Infirmary, affiliated with Harvard Medical School in Boston.

Experts at the University of Sydney found that people who ate three or more portions of oily fish per week reduced the risk of age-related macular degeneration (AMD) by 70 per cent. Those who ate at least one portion of fish every week reduce their risk of developing early AMD by 40 per cent.

"Insufficient essential fatty acid intake could result in abnormal retinal metabolism and cell renewal," while higher levels of omega-3 especially from fish "may protect against retinal oxidation and degeneration," said the report by Brian Chua, BSc, MBBS, MPH, and other researchers on behalf of Westmead Millennium Institute and Vision Co-operative Research Center in Sydney.

Both studies are reported in the July issue of the jourrnal Archives of Ophthalmology. Seddon’s team in the U.S. studied data from 681 individual male twins in their mid-70s who were World War II veterans. The Australian five-year study analysed the dietary intakes of 2258 people 49 and older in Sydney, Australia (average age 64).

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 found in most vegetable oils.

“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." Over-eating omega-6 fatty acids -- found in oils from corn, safflower and sunflower -- diminishes the protective effects of omega-3s.

Limitations of the Research

The studies do not prove that eating fish prevented AMD. Both studies were purely observational; participants weren’t asked to change their diets. The studies also don’t specify what type of fish participants ate, or how the fish was prepared.

Nevertheless, the results are reliable after adjusting for other AMD risk factors. Inflammation might partly explain the results, the researchers note, and omega-3 fats reduce inflammation.

Sources: Media reports and Seddon, J. Archives of Ophthalmology, July 2006; Vol. 124: pp. 995-1001. Chua, B. Archives of Ophthalmology, July 2006; Vol. 124: pp. 981-986.