MONDAY, July 10 (HealthDay News) -- In a study of male twins, researchers have found that those who smoke had an increased risk of developing age-related macular degeneration.

In addition, the researchers found that men who ate more fish rich in omega-3 fatty acids -- such as mackerel, lake trout, sardines, albacore tuna and salmon -- had a lower risk of developing the vision-robbing disease.

Age-related macular degeneration (AMD) is the leading cause of irreversible visual impairment and blindness in people aged 60 and older, and as the population ages the problem will affect more people. Moreover, there's no cure for age-related macular degeneration, though there are treatments that can slow its progression.

The new findings are published in the July issue of the Archives of Ophthalmology.

"Smoking increases the risk of age-related macular degeneration," said study author Dr. Johanna M. Seddon, director of the Epidemiology Unit at the Massachusetts Eye and Ear Infirmary and an associate professor of ophthalmology at Harvard Medical School. "This study of twins provides further evidence that cigarette smoking increases risk, while fish consumption and omega-3 fatty acid intake reduce risk of age-related macular degeneration."

In their study, Seddon and his colleagues collected data on 681 elderly male twins from the National Academy of Sciences National Research Council World War II Veteran Twin Registry.

To determine genetic and environmental risk factors for age-related macular degeneration, the twins were asked about any prior diagnosis of the disease. They also underwent an eye exam and completed a food frequency and a risk-factor questionnaire.

The researchers found that 222 of the twins had intermediate and late-stage age-related macular degeneration, while 459 of the twins had no signs of the disease.

Seddon's team also discovered that current smokers had a 1.9-fold increased risk of developing age-related macular degeneration, while past smokers had about a 1.7-fold increased risk. In addition, the researchers found that eating fish reduced the risk of AMD, particularly if two or more servings were consumed each week. Increased omega-3 fatty acids from fish in the diet were also associated with a lower AMD risk.

While genetics are important in determining who will get AMD, lifestyle choices, such as smoking, play role as well, Seddon said. "Clearly, there is a genetic predisposition to age-related macular degeneration, but that does not necessarily mean you are destined to get the disease," she said.

Seddon recommends a healthy lifestyle to reduce the risk of AMD. "Eat a healthy diet, get exercise, don't smoke, maintain a normal healthy weight," she said.

One expert thinks that 70 percent to 90 percent of the risk for age-related macular degeneration is genetic, but environmental triggers -- such as smoking -- can increase the risk.

"Age-related macular degeneration is a frustrating disease," said Dr. Richard Bensinger, a spokesman for the American Academy of Ophthalmology, and a Seattle ophthalmologist. "We have a population that is aging and higher and higher incidence of this condition, and there is no real treatment for it."

Genetics is the main cause of the disease, Bensinger said. "Heredity interacts with lifestyle," he said. "Cigarette smoking does terrible things throughout the body, and this is one more on the list."

Bensinger does recommend adding more omega-3 fatty acids to the diet and quitting smoking as ways to lower the risk of many diseases, including age-related macular degeneration. "It can be helpful," he said. "But it's no guarantee that you won't develop age-related macular degeneration."

In another study in the same issue of the journal, Australian researchers confirmed that eating fish seems to protect against AMD. Of 2,335 study participants who took part in a five-year follow-up, 158 had developed early AMD and 26 had late-stage disease. Those who ate fish once a week had a 40 percent reduced risk of early AMD, compared with those who ate fish less than once a month. And those who ate fish three or more times a week also had reduced risk for late-stage AMD.

A third study in the journal found that postmenopausal women taking hormone-replacement therapy did not face a greater risk of developing early stage AMD.

University of Michigan researchers studied 4,262 women aged 65 years and older taking hormone-replacement therapy. Of those, 1,627 women were in the estrogen-only group of the study, with 48.1 percent taking hormones and 51.9 percent taking placebo. The other 2,635 women were in the combination hormone trial -- 52.3 percent of those participants were taking estrogen plus progestin pills and 47.7 percent received a placebo. The participants underwent eye assessments and retinal photography at the beginning of the study, between April 2000 and June 2002.

After an average of five years of follow-up, 21 percent of the women had developed AMD. Neither combination nor estrogen-alone therapy was found to be associated with developing the disease, the researchers said.

More information

The U.S. National Eye Institute can tell you more about age-related macular degeneration.

SOURCES: Johanna M. Seddon, M.D., director, Epidemiology Unit, Massachusetts Eye and Ear Infirmary, and associate professor, ophthalmology, Harvard Medical School, Boston; Richard Bensinger, M.D., spokesman, American Academy of Ophthalmology and Seattle ophthalmologist; July 2006 Archives of Ophthalmology

Copyright © 2006 ScoutNews LLC. All rights reserved.