Eating more of the omega-3 fatty acids DHA and EPA, which are found in popular fish-oil supplements, may protect against several common types of blindness, according to a new study.

The study, which focused on blindness caused by abnormal vessel growth, was done on mice, but a clinical trial at Children's Hospital in Boston will soon begin testing the effects of omega-3 on premature babies, who are at particular risk for vision loss.

Abnormal vessel growth causes retinopathy of prematurity, diabetic retinopathy in adults, and "wet" age-related macular degeneration, three leading causes of blindness.

Retinopathy affects about 4 million diabetic patients and about 40,000 premature infants in the United States. It is a two-step disease that begins with a loss of blood vessels in the retina. The retina becomes oxygen-starved and the body responds by growing new blood vessels Unfortunately, the new vessels are malformed, leaky and over-abundant, leading to retinal detachment and blindness.

The researchers fed mice diets rich in either omega-3 fatty acids (comparable to a Japanese diet) or omega-6 fatty acids (comparable to a Western diet). Mice on the omega-3 diet had 40 to 50% less vessel loss in the retina than the omega-6-fed mice. As a result, the omega-3 group had 40 to 50 percent less "bad" vessel growth.

"Our studies suggest that after initial loss, vessels re-grew more quickly and efficiently in the omega-3-fed mice," says one study author. "This increased the oxygen supply to retinal tissue, resulting in a dampening of the inflammatory 'alarm' signals that lead to pathologic vessel growth."

Because omega-3 fatty acids are highly concentrated in the retina, only a 2 percent change in omega-3 intake decreased disease severity by 50 percent, the researchers note.

Omega-3 fatty acids like DHA and EPA are thought to dampen inflammation within the body. They are rare in most Western diets. Premature infants are especially lacking in omega-3 fatty acids, because they need to get this nutrient from their mothers, a transfer that normally happens in the third trimester of pregnancy.

"If omega-3 fatty acids are as effective in humans as they are in mice, simple supplementation could be a cost-effective intervention benefiting millions of people," says another researcher. "The cost of blindness is enormous."

Aside from fish-oil supplements, the most widely available source of omega-3 fatty acids is coldwater oily fish (wild salmon, mackerel, anchovies, sardines). They can also be made synthetically.

Paul A. Sieving, M.D., Ph.D., director of the National Eye Institute, which helped fund the study, said, "This study shows the benefit of dietary omega-3 fatty acids in protecting against the development and progression of retinal disease. It gives us a better understanding of the biological processes that lead to retinopathy and how to intervene to prevent or slow disease. It will be interesting to see if human clinical trials show similar beneficial effects."

The study published was published online by the journal Nature Medicine on June 24, 2007.