In the last years of his life, my father’s biggest sorrow was his failing eyesight, which became worse and worse as his age-related macular degeneration (AMD) progressed. He wasn’t unusual. AMD is the most common cause of visual impairment and blindness in developed countries and, as it mostly affects people over the age of 55, it’s on the rise and our older populationThe group of people being studied. Populations may be defined by any characteristics e.g. where they live, age group, certain diseases. grows. There’s no cure for AMD but the hunt for something that might make a difference and slow its progression preoccupied my father. Like many of us, he was happy to try pretty much anything in the hope that it might help. Often, the things we try cost us money and might be putting us at riskA way of expressing the chance of an event taking place, expressed as the number of events divided by the total number of observations or people. It can be stated as ‘the chance of falling were one in four’ (1/4 = 25%). This measure is good no matter the incidence of events i.e. common or infrequent. of side effects. It’s important to know whether we are taking a stab in the dark or if there’s evidence to tell us something about the likelihood that we’ll be helped, or perhaps harmed.
Can omega 3 dietary supplements help?
One of the things that people might try, to prevent or slow the progress of AMD, is taking omega 3 supplements. There has been some research suggesting that people who have a diet rich in omega 3 fatty acids (from fish oils, for example) are less likely to develop AMD and there’s a plausible biological basis for thinking that it could help too. To understand whether an omega 3 rich diet can affect the development or progression of AMD, a different type of research studyAn investigation of a healthcare problem. There are different types of studies used to answer research questions, for example randomised controlled trials or observational studies. is needed – a randomized controlled trialA trial in which the people taking part are randomly divided into groups. A group (the intervention group) is given the intervention being tested (for example a drug, surgery, or exercise) and compared with a group which does not receive the intervention (the control group). (RCT).
The Cochrane Eyes and Vision Group looked for these RCTs back in 2012 but found none. One of the good things about Cochrane reviewsCochrane Reviews are systematic reviews. In systematic reviews we search for and summarize studies that answer a specific research question (e.g. is paracetamol effective and safe for treating back pain?). The studies are identified, assessed, and summarized by using a systematic and predefined approach. They inform recommendations for healthcare and research. is that they are updated, with the teams looking for evidence again. They have now done this and have found two RCTs to include in their review. In these trialsClinical trials are research studies involving people who use healthcare services. They often compare a new or different treatment with the best treatment currently available. This is to test whether the new or different treatment is safe, effective and any better than what is currently used. No matter how promising a new treatment may appear during tests in a laboratory, it must go through clinical trials before its benefits and risks can really be known., 2343 people were randomly given either omega 3 fatty acid supplements or a dummy pill (placeboAn intervention that appears to be the same as that which is being assessed but does not have the active component. For example, a placebo could be a tablet made of sugar, compared with a tablet containing a medicine.) and they took them for three to five years.
Here’s what they found:
- Omega 3 supplementation for periods up to five years did not slow progression to advanced AMD or reduce significant visual loss compared to a placebo.
- The incidenceThe number of new occurrences of something in a population over a particular period of time, e.g. the number of cases of a disease in a country over one year. of adverse effects (gastrointestinal disorders, bad breath and allergic dermatitis) was similar in the omega 3 and placebo groups
- There was no evidence on the use of omega 3 supplements to prevent AMD
How good was the evidence?
The evidence on the rateThe speed or frequency of occurrence of an event, usually expressed with respect to time. For instance, a mortality rate might be the number of deaths per year, per 100,000 people. of progression of AMD was high quality and for the other outcomesOutcomes are measures of health (for example quality of life, pain, blood sugar levels) that can be used to assess the effectiveness and safety of a treatment or other intervention (for example a drug, surgery, or exercise). In research, the outcomes considered most important are ‘primary outcomes’ and those considered less important are ‘secondary outcomes’. it was moderate quality.
Where does this leave us?
There is no evidence from RCTs to support increasing omega 3 intake in order to prevent or slow AMD.
Important things we still don’t know:
- Whether omega 3 supplementation prevents AMD
- Whether the effects of taking omega 3 supplements is different in different populations (does ethnicity, nutritional status, or the stage of AMD make a difference, for example?)
- Whether the composition or source (such as oily fish versus fish oil supplements) of the omega 3 makes a difference
There has been a great deal of research into the potential health benefits of omega 3, including a number of Cochrane reviews, and most often the conclusions reached are that more research is needed. The authors of this review suggest that a cost-effective approach would be to include AMD outcomes in large trials of other diseases and they found one that is currently ongoing.
Let’s hope that future updates of this review will be able to draw on more high quality evidence to help answer some of the remaining questions.
Links:
Lawrenson JG, Evans JR. Omega 3 fatty acids for preventing or slowing the progression of age-related macular degeneration. Cochrane Database of Systematic ReviewsIn systematic reviews we search for and summarize studies that answer a specific research question (e.g. is paracetamol effective and safe for treating back pain?). The studies are identified, assessed, and summarized by using a systematic and predefined approach. They inform recommendations for healthcare and research. 2015, Issue 4. Art. No.: CD010015. DOI: 10.1002/14651858.CD010015.pub3.
