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Full Title: Effects of Omega-3 Fatty Acids on Eye Health
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Objectives: To systematically review the scientific-medical literature regarding the possible primary or secondary preventive influence of the intake of omega-3 fatty acids on important eye health-related outcomes.
Data Sources: MEDLINE®, PreMEDLINE®, EMBASE, Cochrane Central Register of Controlled Trials, CAB Health, and Dissertation Abstracts. Searches were not restricted by language of publication, publication type, or study design except with the MeSH® term "dietary fats," which was limited by study design to increase its specificity. Search terms related to omega-3 fatty acids and eye health. Additional published or unpublished literature was sought through manual searches of reference lists of included studies and key review articles, and from the files of content experts.
Review Methods: Studies were considered relevant if they described live human populations of any age, involved any type of study design, and investigated the intake of any foods or extracts, known to contain omega-3 fatty acids, for their possible primary or secondary preventive influence on eye health.
Results: Sixteen studies, described in 16 published journal articles, were found to investigate nine of 23 potential questions. Question-specific qualitative syntheses of the evidence were derived. Greater interpretative emphasis was placed on evidence from randomized controlled trials (RCTs) and other designs that were both prospective and controlled. Too little, or flawed, available evidence precluded meta-analysis for each question.
Conclusions: Based on the studies identified by this review, clinical research has only scratched the surface with respect to understanding the possible utility of the intake of omega-3 fatty acids as a primary or secondary prevention in eye health. Moreover, seen from the point of view of clinical research's typical, linear arc—which moves from basic science to observational research to RCTs, and culminating in the systematic review/meta-analysis of the observations obtained by these primary studies—there is a paucity of solid observational research with which to construct an experimental framework affording the meaningful conduct of RCTs.
For example, there is little understanding of the exact sources, types, and doses of omega-3 fatty acids, or even the possible duration of their use, which might usefully serve as definitions of a prevention-centered "intervention" for any of the eye diseases/visual impairments examined in our review. Perhaps only with respect to the question of preventing the development/progression of advanced ARMD is there some suggestive evidence, which is underscored by it being a strong public health problem, to allow researchers to consider conducting an RCT. At the same time, a single study reporting adverse event data likely does not permit laying to rest all possible concerns regarding the short- or long-term safety of omega-3 fatty acid interventions.
More research is needed with respect to the effects of omega-3 fatty acids on eye health. Also, determining the possible benefits of the intake of omega-3 fatty acids in eye health might profit from considering the impact of the concurrent intake of omega-6 fatty acids and, by definition, the omega-6/omega-3 fatty acid intake ratio.
Effects of Omega-3 Fatty Acids on Eye Health
Evidence-based Practice Center: University of Ottawa
Topic Nominator: Office of Dietary Supplements, National Institutes of Health
Current as of July 2005