Posted: July 18, 2006

Eating fish on a frequent and regular basis may decrease the chances of developing age-related macular degeneration, while smoking nearly doubles the risk, and hormone therapy appears to have no effect at all in preventing this most-common cause of elderly vision loss, according to three articles in the current issue of Archives of Ophthalmology.

 

In the first study, scientists at the Massachusetts Eye and Ear Infirmary in Boston investigated genetic and environmental risk factors for AMD in 681 elderly male twins.

 

Of the 681 men, 222 (average age 75.9 years) had intermediate or late-stage AMD and 459 (average age 74.5 years) had no AMD or were in the very early stages. Those who currently smoked had a 1.9-fold increased risk of AMD, and those who had smoked in the past had a 1.7-fold increased risk.

 

Those who ate more fish and more omega-3 fatty acids (found in salmon and other fish) were less likely to have AMD. The greatest reduction in risk was seen among individuals who ate two or more servings of fish per week.

 

"About a third of the risk of AMD in this twin study cohort could be attributable to cigarette smoking, and about a fifth of the cases were estimated as preventable with higher fish and omega-3 fatty acid dietary intake," they conclude.

 

In a second study, researchers from the Westmead Millennium Institute and Vision Co-operative Research Centre in Sydney, Australia, examined the association between dietary fat intake and AMD risk in 2,895 Australians age 49 years or older, beginning in 1992-1994.

 

At the beginning of the study and again five years later, participants had a comprehensive eye exam that included photographs of the retina.

 

Of the 2,335 participants who participated in the five-year follow-up, 158 had developed early AMD and 26 had late-stage AMD. After adjusting for other factors that may influence risk, including smoking, age, gender and vitamin C intake, those in the group with the highest intake of polyunsaturated fat had a 50% reduced chance of developing early AMD compared with those who ate the least.

 

Those who ate fish once a week had a 40% reduced risk of early AMD compared with those who ate fish less than once per month, and those who ate fish three or more times per week also had reduced risk for late-stage AMD.

 

Interestingly and contrary to previous studies showing an increased risk for AMD with higher unsaturated fat intake, no link was found between AMD and consumption of butter, margarine or nuts, which all contain high levels of unsaturated fats.

 

"To explain our findings, we suggest that insufficient essential fatty acid intake could result in abnormal retinal metabolism and cell renewal," the authors write.

 

Postmenopausal hormone therapy does not appear to increase or decrease the overall risk of AMD among women, although combination hormones may slightly reduce the chances of developing certain risk factors or types of the condition, according to a third report in the same issue.

 

Researchers studied 4,262 women age 65 years and older who were part of the Women's Health Initiative Sight Exam Study, part of the larger Women's Health Initiative clinical trial of hormone therapy.

 

Of those, 1,627 were in the estrogen-only group of the study, with 48.1% taking hormones and 51.9% taking placebo. The other 2,635 women were in the combination hormone trial; 52.3% of those participants were taking estrogen plus progestin pills and 47.7% received placebo

 

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

 

Among women in the combination trial only, active hormone therapy was associated with a slightly reduced risk of developing soft drusen-deposits in the eye that may precede AMD-and also lower odds of having neovascular AMD, a less common form of the condition in which blood vessels grow underneath the retina, impairing vision.

 

"We conclude that treatment with hormones does not influence the occurrence of early AMD," the authors conclude. "As an exception, a possible protective effect was found for soft drusen or neovascular AMD in relation to combined equine estrogens plus progestin."

 

Age-related macular degeneration (AMD) occurs when the macula, the area at the back of the retina that produces the sharpest vision, begins to deteriorate. The condition affects approximately 30% of Americans age 75 years and older, with 6%-8% developing advanced cases.

 

AMD is the most prevalent cause of vision loss and blindness in the elderly population.

 

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