Omega 3 (2006) & Macular Degeneration

This article discusses two key studies about the relationship between omega-3 intake and macular degeneration.

Design of the Studies:

1. Observational prospective study -- mean follow of 5 years
2. Observational retrospective study

Participants:

1. 2895 adults > 49 years of age at baseline for whom baseline food frequency questionnaire (FFQ) data were available.
2. 681 elderly male twins of whom 222 had age-related macular degeneration (AMD) and 459 did not.

Main Outcome Measures:

1. FFQ data were analyzed, looking for variables associated with the risk of AMD.
2. Subjects were grouped by smoking status and by quantity and quality of dietary fat intake.

Key Findings:

1. Subjects in the highest quintile of omega-3 fatty acid intake had a 59% lower risk for AMD compared with those in the lowest quintile of intake (95% CI, 0.22-0.75). Those eating fish once per week had a 42% reduction in risk compared with those with a minimal fish intake (95% CI, 0.37-0.90). Those consuming fish > three times per week had a 75% reduced risk (95% CI, 0.06-1.00).
2. After multivariate analysis, those consuming fish > twice per week had a statistically significant 37% reduction in risk compared with those consuming less than one serving per week. Those with a median intake of 350 mg of omega-3 oil (the top quartile of intake) had an adjusted 45% lower risk of AMD compared with those consuming only 60 mg/day (the lowest quintile of intake, p=0.02). The protection associated with EPA/DHA intake occurred primarily in those consuming relatively low levels of linoleic acid (adjusted odds ratio of 0.23, p<0.001). Current smokers had almost twice the risk for AMD compared with those who never smoked (p=0.06).

Practice Implications:

Allopathic treatment for AMD is relatively ineffective for most patients. Until now, most of the emphasis in prevention and treatment in the realm of natural medicine has focused on the use of lutein and zinc, though a small body of evidence suggested fish consumption might reduce the risk of AMD (Arch Ophthalmol 2000;118:401-4). Both new studies confirm a strong and consistent inverse correlation between EPA, DHA, and fish consumption and AMD.

The study by Chua and colleagues also tracked alpha-linolenic acid (ALA) intake -- the vegetarian omega-3 oil that partially bioconverts to EPA. In terms of 5-year risk for early AMD, ALA showed the same protective effect, as did EPA/DHA. However, though this difference was not statistically significant, for late AMD, those in the lowest quintile of ALA intake had a lower risk than those consuming more ALA. Until more is known, therefore, there is little reason to assume ALA has the same protective effect that EPA and DHA appear to have.

Chua's findings regarding associations between total fat, monounsaturated fatty acids, trans fatty acids, polyunsaturated fatty acids [PUFA], and saturated fatty acids, and AMD risk conflict with previously published research (Arch Ophthalmol 2003;12:1728-37). Therefore, we don't know enough about the possible effects of these variables to alter clinical practice.

Findings from the study by Seddon and colleagues, suggest that cessation from smoking combined with a modest increase in fish or omega-3 fatty acid intake would literally cut the risk for AMD in half. Implementing appropriate changes could save vision in many elderly people. But what sense do these findings make?

Experimental reports show that DHA protects against retinal oxidative damage. Also, an inflammatory component to AMD has been reported, and EPA and DHA have known antiinflammatory actions. That said, for the most part we still do not understand how EPA and DHA protect against AMD.

Despite a lack of understanding, encouraging patients to increase intake of fatty fish makes sense. After considering the favorable risk-to-benefit ratio, an argument can also be made for discussing supplementation of EPA/DHA with AMD patients. Optimal dosing remains unclear, but even a few hundred milligrams per day of EPA plus DHA would reach well into the dietary intake reported by those experiencing a protective effect.

References

1. B. Chua, V. Flood, et al. Dietary fatty acids and the 5-year incidence of age-related maculopathy. Archives of Ophthalmology, July 2006
2. J.M. Seddon, S. George, et al, Cigarette smoking, fish consumption, omega-3 fatty acid intake, and associations with age-related macular degeneration. Archives of Ophthalmology, July, 2006.

Author: Steve Austin, N.D.