Smoke Gets in Your Eyes

BOSTON, July 11 -- Elderly male smokers have nearly twice the risk of age-related macular degeneration as elderly brethren who don't smoke, according to researchers here.

On the other hand, eating two or more servings of fish a week sharply reduced the risk, as did a diet rich in omega-3 fatty acids, Johanna Seddon, M.D., of the Massachusetts Eye and Ear Infirmary, and colleagues, reported in the July issue of Archives of Ophthalmology.

They drew their conclusions after analysis of a cohort of 681 individual twins enrolled in the National Academy of Sciences-National Research Council World War II Veteran Twin Registry. The findings provide "further evidence that cigarette smoking increases risk while fish consumption and omega-3 fatty acid intake reduce risk of age-related macular degeneration," the researchers concluded.

More than 12,000 twins living at the start of the study were screened. The 681 participants -- 358 monozygotic and 323 dizygotic -- were all pairs in which one or both twins reported a diagnosis of age-related macular degeneration, as well as a subset in which neither twin reported age-related macular degeneration. Enrolled men whose twin was subsequently unable to participate were also included.

All participants were given eye examinations and had their height, weight and blood pressure measured. They filled out questionnaires about their diets, risk factors and cardiovascular history.

The study found:

• Current smokers were nearly twice as likely to have age-related macular degeneration as never-smokers. The odds ratio was 1.9, with a 95% confidence interval from 0.99 to 3.68; the result approached statistical significance at P=0.06.
• Former smokers also had an increased risk. The odds ratio was 1.7, with a 95% confidence interval from 1.2 to 2.6; the result significant at P=0.009.
• Eating more fish -- particularly for two or more servings a week -- reduced the risk; the P value for the trend was 0.04.
• Dietary omega-3 fatty intake was inversely associated with age-related macular degeneration -- the odds ratio, comparing the lowest versus the highest quartile, was 0.55, with a 95% confidence interval from 0.32 to 0.95.

The researchers calculated that the attributable risk percentage for smoking was 32%, while the preventive fraction for higher omega-3 intake was 22%.

The findings gave strength to the hypothesis that age-related macular degeneration and cardiovascular disease share some of the same modifiable factors, such as cigarette smoking and lipid levels, as well as some of the antecedents, such as oxidative stress and inflammatory processes, Dr. Seddon and colleagues said.

Using the same twin registry, Dr. Seddon and colleagues had previously shown that age-related macular degeneration is highly heritable and that markers of inflammation, such as C-reactive protein and plasma homocysteine are associated with age-related macular degeneration, are associated with the disease.

The message for clinicians, the researchers said, is that patients should be advised on diet and modifiable risk factors. "It may be reasonable for physicians to make dietary recommendations for eye health," they said, as well as discouraging smoking as much as possible.

They also pointed out a potential limitation of the study. "Because this is a case-control design, we cannot exclude the possible effect of unmeasured lifestyle or dietary differences," they wrote.