Review question
We asked the question whether increased dietary intake of omega 3 fatty acids prevented or slowed the progression of age-related macular degeneration.
Background
Age-related macular degeneration (AMD) is an eye condition that affects the central area of the retina (light-sensitive tissue at the back of the eye). AMD is associated with a loss of detailed vision and adversely affects tasks such as reading, driving and face recognition. In the absence of a cure, there has been considerable interest in the role of modifiable risk factors to prevent or slow down the progression of AMD. Evidence from population studies suggests that people who have a diet with relatively high levels of omega 3 fatty acids (such as those derived from fish oils) are less likely to develop AMD.
Study characteristics
We searched for studies up to 2 February 2015. We identified two trials with a total of 2343 participants. The trials were conducted in the USA and France and investigated the use of fish oil supplements in people with AMD who were at high risk of progressing to advanced disease. We judged the studies to be at low risk of bias. One study was funded by government grants and the other study was funded by the manufacturer of the dietary supplement.
Key results
These studies found that omega 3 supplementation for periods up to five years did not reduce the rate of progression to advanced AMD or reduce significant visual loss compared to a placebo. The incidence of adverse effects was similar in the intervention and placebo groups.
Quality of the evidence
We judged the quality of the evidence on rate of progression to AMD to be high, and the quality of the evidence for other outcomes to be moderate because the estimates were imprecise.
This review found that omega 3 LCPUFA supplementation in people with AMD for periods up to five years does not reduce the risk of progression to advanced AMD or the development of moderate to severe visual loss. No published randomised trials were identified on dietary omega 3 fatty acids for primary prevention of AMD. Currently available evidence does not support increasing dietary intake of omega 3 LCPUFA for the explicit purpose of preventing or slowing the progression of AMD.
Evidence from animal models and observational studies in humans has suggested that there is an inverse relationship between dietary intake of omega 3 long-chain polyunsaturated fatty acids (LCPUFA) and risk of developing age-related macular degeneration (AMD) or progression to advanced AMD.
To review the evidence that increasing the levels of omega 3 LCPUFA in the diet (either by eating more foods rich in omega 3 or by taking nutritional supplements) prevents AMD or slows the progression of AMD.
We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2015, Issue 1), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to February 2015), EMBASE (January 1980 to February 2015), Latin American and Caribbean Health Sciences Literature Database (LILACS) (January 1982 to February 2015), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 2 February 2015.
We included randomised controlled trials (RCTs) where increased dietary intake of omega 3 LCPUFA was compared to placebo or no intervention with the aim of preventing the development of AMD, or slowing its progression.
Both authors independently selected studies, assessed them for risk of bias and extracted data. One author entered data into RevMan 5 and the other author checked the data entry. We conducted a meta-analysis for one primary outcome, progression of AMD, using a fixed-effect inverse variance model.
We included two RCTs in this review, in which 2343 participants with AMD were randomised to receive either omega 3 fatty acid supplements or a placebo. The trials, which had a low risk of bias, were conducted in the USA and France. Overall, there was no evidence that people who took omega 3 fatty acid supplements were at decreased (or increased risk) of progression to advanced AMD (pooled hazard ratio (HR) 0.96, 95% confidence interval (CI) 0.84 to 1.10, high quality evidence). Similarly, people taking these supplements were no more (or less) likely to lose 15 or more letters of visual acuity (USA study HR 0.96, 95% CI 0.84 to 1.10; French study at 36 months risk ratio (RR) 1.25, 95% CI 0.69 to 2.26, participants = 230). The number of adverse events was similar in the intervention and placebo groups (USA study participants with one or more serious adverse event RR 1.00, 95% CI 0.91 to 1.09, participants = 2080; French study total adverse events RR 1.05, 95% CI 0.97 to 1.13, participants = 263).