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Dietary fat and fish intake may be associated with ARM
Cross-sectional study also finds link between cholesterol and late ARM.
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SYDNEY — Dietary intake of fat or fish may be associated with age-related maculopathy (ARM), according to the results of a cross-sectional, urban population-based study of 3,654 people 49 years or older.
“People who consumed fish regularly had a decreased likelihood for having the late form of ARM,” said co-author Paul Mitchell, MD, an associate professor of ophthalmology at the University of Sydney. “There was a fair number of people in the community who ate fish on some sort of regular basis. But people who ate fish rarely had essentially double the chance of having late ARM compared with those who ate fish at least moderately frequently. However, we were unable to demonstrate a dose relationship.”
The study, recently published in Archives of Ophthalmology, noted that the human retina and macula contain a high proportion of polyunsaturated omega-3 fatty acids, in particular docosahexaenoic. “Docosahexaenoic acid is found predominately in oily fish and offal and appears to play an important role in the normal functioning of the retina,” stated the authors.
Food questionnaire
The study recruited participants from two postal codes in Sydney. “About 83% of eligible residents participated,” Dr. Mitchell told Ocular Surgery News. “The subjects underwent a detailed eye examination, and photographs were taken of the retina in both eyes, which were then graded by masked graders. The levels of ARM were decided at that grading.” Participants also were administered a detailed food-frequency questionnaire. “This questionnaire outlined all the various foods that they consumed on average per week for the past year,” Dr. Mitchell said. The questionnaire also took into account seasonal foods.
The food-frequency questionnaire was validated by weighed food records in about 150 subjects. “These participants were instructed by a dietitian about how to weigh their food and keep very accurate records of foods they ate in a 4-day period over three different seasons,” Dr. Mitchell said. “We found that the weighed food records were actually quite close to most nutrients reflected in the food-frequency questionnaire.”
Despite similar findings between ARM and dietary fat intake in both the Australian study and the Beaver Dam Eye Study, the latter study reported no associations between ARM and seafood consumption. “That study was conducted in Wisconsin, and although it is on the lake, it may be that in Wisconsin the frequency of consuming fish is lower than in Australia,” Dr. Mitchell said. “We have started to look at comparisons between the two populations. The populations are very similar. The Wisconsin population is largely Northern European-derived, and so is ours.”
Threshold protective effect
The current study’s data suggest the possibility of a threshold protective effect at low levels of fish intake, but no increased protection from ARM at increased fish intake. “Consumption of high-fish diets by the elderly has been shown to compromise the status of vitamin E, an important antioxidant needed by the retina,” Dr. Mitchell said. “This could explain the threshold protective effect from dietary fish.”
In any event, “ARM increases dramatically with increasing age,” Dr. Mitchell said. “The main environmental risk factor found to date is cigarette smoking. In our analysis, we adjusted for increasing age, family history, gender and whether or not an individual smoked. Women seem to develop the disease slightly more frequently than men.” Dr. Mitchell said the two main risk factors for ARM are genetics and cigarette smoking. “In our population, smokers had about 4.5 times the likelihood of having ARM than people who didn’t smoke,” he said. “Many other studies also have found this strong smoking relationship.”
Cholesterol impact
The study also found that people with higher intakes of cholesterol “were significantly more likely to have late ARM,” Dr. Mitchell said. “This was an odds ratio of 2.7. The lowest quintile had a median intake of about 200 mg per day, while the highest quintile had a median intake of about 460 mg per day.”
Total and saturated fat intake were associated with a borderline significant increase in risk for early ARM (over-refractions of 1.5 and 1.6, lowest quintile and highest quintile, respectively). However, there was a significant association (P=.05) for increasing prevalence of early ARM with increasing monounsaturated fat intake.
Dr. Mitchell said that one of the other dietary factors for ARM is consumption of antioxidant vitamins (vitamins A, C and E; particularly vitamin A as beta-carotene). “A number of studies have found associations between this disease and antioxidant vitamin intake, although certainly the findings are not consistent in cross-studies. Overall, only about one-half of the studies that have looked at antioxidant vitamins have found an association with ARM,” he said. “We looked at antioxidant vitamins, but could not find any association.”
Nonetheless, “our study provides supportive evidence that dietary fat intake might be a risk factor for ARM,” Dr. Mitchell said. “The dietary fat guidelines that are recommended for prevention of heart disease and stroke — eating a diet that is low in cholesterol, high in polyunsaturates and rich in fish — is probably worthwhile in protecting your eyes as well as your heart.”
For Your Information:Reference:
- Paul Mitchell, MD, can be reached in c/o of The Eye Clinic, Westmead Hospital, Westmead, NSW 2145, Australia; (61) 2-9845-7960; fax: (61) 2-9845-6117; e-mail: mitchell@bigpond.net.au.
- Smith S, Mitchell P, Leeder SR. Dietary fat and fish intake and age-related maculopathy. Arch Ophthalmol. 2000;188:401-404.