June 4, 2009 — Regular consumption of fish, nuts, olive oil, and other foods containing omega-3 fatty acids and avoidance of trans fats appear to be associated with a lower risk for the eye disease age-related macular degeneration (AMD), according to 2 studies reported in the May issue of the Archives of Ophthalmology.

Blue Mountains Eye Study

"The role of dietary fatty acids in AMD was initially examined because of the hypothesis that AMD and cardiovascular disease may share a similar pathogenesis, and fat intake has been associated with atherosclerosis and cardiovascular disease," write Jennifer S.L. Tan, MBBS, BE, from Westmead Millennium Institute, Westmead Hospital in Sydney, Australia, and colleagues from the Blue Mountains Eye Study.

"There is increasing evidence of a benefit from regular dietary fish and omega-3 (PUFA) [polyunsaturated fatty acid] intake on the risk of AMD, particularly in people with a lower ratio of omega-6 to omega-3 PUFAs. However, evidence of the association between AMD and total fat or other fat types, such as saturated and monounsaturated fatty acids, is inconsistent."

The goal of this study was to examine the association between baseline dietary fatty acids and 10-year incident AMD in an elderly Australian cohort. AMD was evaluated from retinal photographs in 3654 participants at baseline and in 2454 participants 5 and/or 10 years later. The participants also completed a semiquantitative food frequency questionnaire.

Eating 1 serving of fish per week was associated with lower risk for incident early AMD, after adjustment for age, sex, and smoking (relative risk [RR], 0.69; 95% confidence interval [CI], 0.49 - 0.98). This association was particularly driven by participants with less than the median consumption of linoleic acid (RR, 0.57; 95% CI, 0.36 - 0.89).

Results were similar for dietary consumption of long-chain omega-3 PUFAs. The risk for incident early AMD was lower in participants who consumed 1 to 2 servings of nuts per week (RR, 0.65; 95% CI, 0.47 - 0.91). Protective associations between nut consumption and lower risk for pigmentary abnormalities were evident in nonsmokers, in participants with less than the median ratio of serum total to high-density lipoprotein cholesterol levels, and in those with greater than the median level of beta carotene intake.

"This study provides evidence of protection against early AMD from regularly eating fish, greater consumption of omega-3 polyunsaturated fatty acids, and low intakes of foods rich in linoleic acid," the study authors write. "Regular consumption of nuts may also reduce AMD risk. Joint effects from multiple factors are suggested."

Limitations of this study include possible recall or survival bias; moderate losses to follow-up, introducing possible bias; and the possibility of chance findings caused by examination of many associations.

"Joint effects on AMD risk are suggested between the consumption of fish, nuts, or long-chain omega-3 PUFAs and other factors, including smoking, intake of omega-6 PUFAs or beta carotene, and the ratio of serum total cholesterol to HDL-C [high-density lipoprotein cholesterol]," the study authors conclude.

"These findings also suggest that an appropriate balance among various nutrients is essential for maximizing nutritional benefit. Further studies, particularly clinical trials such as the AREDS [Age-Related Eye Disease Study] extension trial, should provide important evidence of whether dietary intervention or supplementation with long-chain omega-3 PUFAs could prevent or delay the development of this significant cause of blindness."

Melbourne Collaborative Cohort Study

The objective of the second study, the Melbourne Collaborative Cohort Study, by Elaine W.-T. Chong, MD, PhD, MEpi, from the Centre for Eye Research Australia in Melbourne, and colleagues, was to examine the relationship between past dietary fat intake and the prevalence of AMD in a cohort of 6734 Australian participants aged 58 to 69 years in 1990 to 1994.

The participants completed a food frequency questionnaire at baseline to estimate nutrient intakes, and bilateral digital macula photographs were evaluated for early and late AMD signs at follow-up from 2003 to 2006. Odds ratios (ORs) were estimated from logistic regression, after adjusting for age, smoking, and other potential confounders.

Higher dietary consumption of trans-unsaturated fats was associated with an increased prevalence of late AMD. Comparing the highest with the lowest quartile of trans fat intake, the OR for late AMD was 1.76 (95% CI, 0.92 - 3.37; P =.02), whereas greater intake of omega-3 fatty acids was inversely associated with early AMD (OR for highest quartile vs lowest quartile, 0.85; 95% CI, 0.71 - 1.02; P = .03).

The prevalence of late AMD was lower for olive oil intake of 100 mL/week or more vs less than 1 mL/week (OR, 0.48; 95% CI, 0.22 - 1.04; P = .03). No significant associations with AMD were noted for intakes of fish, total fat, butter, or margarine.

"A diet low in trans-unsaturated fat and rich in omega-3 fatty acids and olive oil may reduce the risk of AMD," the study authors write.

Limitations of the study include those inherent in the food frequency questionnaire, failure to differentiate between intake of nonoily and oily fish, use of multiple comparisons, possible residual confounding, and the possibility that olive oil may also be a proxy for certain healthy lifestyles.

"We found that higher TFA [trans-unsaturated fatty acid] intake was associated with an increased prevalence of late AMD, while omega-3 fatty acids and olive oil were associated with a reduced prevalence of early and late AMD, respectively,” the study authors conclude. “Our findings suggest that people who follow a diet low in processed foods high in TFA and rich in omega-3 fatty acids and olive oil might enjoy some protection from developing AMD."

The Australian National Health and Medical Research Council supported the Blue Mountains Eye Study. The Melbourne Collaborative Cohort Study was supported by the National Health & Medical Research Council, Royal Victorian Eye and Ear Hospital Wagstaff fellowship, the Ophthalmic Research Institute of Australia, John Reid Charitable Trust, and Perpetual Trustees. The authors of both studies have disclosed no relevant financial relationships.

Arch Ophthalmol. 2009;127:656-665; 674-680.