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Omega-3 Fatty Acids and Risk of AMD

According to AMD Alliance International, AMD affects approximately 25-30 million people worldwide, and the incidence of this disease is projected to triple by 2025. New treatments for AMD are limited to patients with exudative AMD and are not without risks. Thus, primary prevention of AMD by modifying risk factors remains an important public health strategy.

Insufficient intake of certain dietary components may be one of those risk factors. There is growing interest in the long - chain omega-3 fatty acids EPA and DHA since they play an important role in the layer of nerve cells in the retina and may be involved in the prevention or progression of AMD.

Epidemiological studies have generally shown inverse associations between intake of these fatty acids from fish and AMD. Now, a systematic review and meta-analysis from the University of Melbourne reports that higher intakes of EPA and DHA significantly decrease the risk of both early and late AMD (1).

Study Design and Methods

Seven databases were systematically searched using standardized criteria, with no limits on publication year or language. Randomized controlled trials and prospective cohort, case-control, and cross-sectional studies were included. Of 2,754 abstracts identified, 3 prospective cohort, 3 case-control, and 3 cross-sectional studies met the criteria. Measures of associations were pooled quantitatively using meta-analytic methods.

Results

Nine studies provided data on a total sample of 88,974 people including 3,203 AMD cases.

A high dietary intake of omega-3 fatty acids was associated with a 38% reduction in the risk of late AMD, when the highest intake was compared with the lowest (pooled odds ratio [OR], 0.62; 95% confidence interval [CI], 0.48-0.82).

Fish intake at least twice weekly was associated with a 24% and 33% reduced risk of early and late AMD respectively (pooled OR, 0.76; 95% CI, 0.64-0.90; and pooled OR, 0.67; 95% CI, 0.53-0.85).

Combining the results from all 9 studies also showed that a high dietary intake of EPA was linked to a 23% lower risk of early AMD, while DHA was associated with a 30% reduction.

In contrast, a high intake of the omega-3 alpha linolenic acid was associated with a 49% increase in risk.

Comments

In this study the definition of 'early AMD' included vision loss, and hence might be more indicative of an intermediate stage of AMD. However, the findings suggest that a greater intake of EPA and DHA can slow AMD progression. In addition, results from the current analysis are consistent with another systematic review in which the authors critically reviewed 6 observational studies for evidence that omega-3 fatty acids prevent AMD (2).

While the benefits of EPA and DHA require confirmation in long-term intervention trials such as AREDS-2, the authors underscore the strong underlying biological rationale of these fatty acids.

DHA plays an essential structural role in the membrane of the retina and is found in high concentrations. Further, the outer photoreceptor cell segments of the retina are constantly shed in the normal visual cycle and deficiency of DHA could initiate AMD.

According to the authors: "There is also evidence that such long-chain fatty acids protect against oxygenic, inflammatory, and age-associated pathology of the vascular and neural retina, which are possible pathogenic factors for AMD development."

References

1. W-T Chong E, et al. Dietary omega-3 fatty acid and fish intake in the primary prevention of age-related macular degeneration. A systematic review and meta-analysis. Arch Ophthalmol 126:826-33, 2008.
2. Hodge WG, et al. Efficacy of omega-3 fatty acids in preventing age-related macular degeneration: a systematic review. Ophthalmology 113:1165-1172, 2006.