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Support for Macular Benefits of Omega-3

Reviewers from the National Eye Institute recently summarized the functions of the omega-3 fatty acids eicosapentenoic acid (EPA) and docosapentaenoic acids (DHA) in retinal tissues. [See EduFacts, Vol. 5 No 7]. According to the reviewers, studies looking at the relationship of the omega-3 fats to the prevalence of advanced AMD have generally observed a protective effect. A new study by Australian researchers adds to this growing body of evidence, and suggests that regularly consuming omega-3 fat, especially from fish, protects against early and late AMD in older individuals (1).

Design and Methods

To assess longitudinal associations between dietary fat and incident AMD, dietary intakes were measured by food frequency questionnaires at baseline in 2895 participants of the Blue Mountains Eye Study (BMES). Since the questionnaires can under- or over-report food consumption, dietary data were verified in a sub- group of participants who completed 4-day weighed food records 3 times over the course of a year. The results were generally in good agreement with the questionnaire data. Seventy five percent of the BMSE cohort (2335 persons) was re-examined after 5 years. Presence of AMD was graded from retinal photographs (Wisconsin ARM Grading System). Logistic regression adjusted for age, sex, vitamin C intake and smoking.

Results

The researchers examined the risk of incident AMD participants in the lowest and highest quintiles of dietary fat intakes with respect to the 60% of the population who represent a moderate, normal intake, or those in the middle 3 quintiles. Participants in the highest vs. the lowest quintiles of omega-3 fat intake had a lower risk of incident early AMD (odds ratio 0.41 [0.22-0.75])

A 40% reduction of incident early ARM was associated with fish consumption at least once a week (odds ratio 0.58 [0.37-0.90]). Consuming fish at least 3 times weekly resulted in about a 70% reduction in the incidence of late AMD (odds ratio 0.25 [0.06-1.00]). (See Table)

When the intake of specific types of fats was calculated, a trend toward increased risk of developing early AMD was noted for people with the lowest intake of monounsaturated fats and omega-3 including alpha-linolenic acid.

Comments

Though several population health studies have linked high dietary fat intake from any source to increased AMD risk, this study found no evidence that dietary fat of any kind raised that risk. The findings are largely in agreement with other studies showing that diets high in omega-3 fatty acids, particularly DHA derived largely from fish, may protect against retinal oxidation and degeneration, according to the authors. They propose that insufficient omega-3 intake could cause abnormal metabolism in the retina and affect cell renewal.

ORs and CIs of Early and Late ARM with Increasing Frequency of Certain Food Types in BMES Participants*
		5-y Incidence, OR (95% CI)
		Early ARM (n = 130)	Late ARM (n = 22)
Margarine
	<1/wk	1.00 (Reference)	1.00 (Reference)
	1-6/wk	.89 (0.57-1.38)	1.55 (0.44-5.40)
	Daily	0.87 (0.58-1.29	0.85 (0.33-2.22)
Butter
	<1/wk	1.00 (Reference)	1.00 (Reference)
	1-6/wk	0.48 (0.22-1.02)	0.82 (0.18-3.76)
	Daily	0.77 (0.48-1.24)	0.85 (0.27-2.66)
Total Fish †
	< 1/mo	1.00 (Reference)	1.00 (Reference)
	≥1/wk	0.48 (0.37-0.90)	0.44 (0.16-1.21)
	≥3/wk	0.62 (0.38-1.03)	0.25 (0.06-1.00)
Nuts
	Never	1.00 (Reference)	1.00 (Reference)
	≥ 1/wk	0.80 (0.52-1.25)	0.82 (0.29-2.34)
	≥ 1/wk	0.79 (0.46-1.34)	0.55 (0.14-2.16)
Abbreviations: ARM, age-related maculopathy; BMES, Blue Mountains Eye Study; CI, confidence interval; OR, odds ratio. *Food types are categorized by frequency of servings. † Includes sardines, tuna, and other fish.

References

1. Chua B, et al. Dietary fatty acids and the 5-year incidence of age-related maculopathy. Archives Ophthalmol 124:981-6, 2006.