This article discusses two key studies about the relationship between omega-3 intake and macular degeneration.
Design of the Studies:
- Observational prospective study — mean follow of 5 years
- Observational retrospective study
Participants:
- 2895 adults > 49 years of age at baseline for whom baseline food
frequency questionnaire (FFQ) data were available. - 681 elderly male twins of whom 222 had age-related macular degeneration
(AMD) and 459 did not.
Main Outcome Measures:
- FFQ data were analyzed, looking for variables associated with the risk
of AMD. - Subjects were grouped by smoking status and by quantity and quality of
dietary fat intake.
Key Findings:
- 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). - 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.