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A recent highly publicised Cochrane review on fish oils made headlines by claiming omega 3 from fish oils had little or no effect on heart health. [i] The review, ‘Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease’, aimed to investigate the effects of increased omega-3 intake on mortality and cardiovascular events. The authors concluded that evidence suggests omega-3 supplementation has little or no effect on cardiovascular health. Although this review was conducted using rigorous assessment of evidence quality, there are a multitude of other factors which the review fails to consider, which has led us to therefore question this conclusion.
One key problem with ‘meta analyses’ like these is that they include lots of different studies to increase the population, hoping to see a more accurate result. But they also tend to aggregate a lot of studies together that are very different.
Firstly, there are significant differences in the populations within the studies included. Although the degree of illness was considered and discussed as part of the inclusion criterion, the implications of this were not considered. The review consolidated findings of studies conducted in both healthy individuals and those with pre-existing health conditions, in almost equal proportions. The health conditions included were those such as cardiovascular disease, previous heart attacks and coronary surgery, as well as conditions not related to cardiovascular health, such as cancer. For these individuals, mortality risk in general could be considered higher than for healthy individuals, as all-cause mortality, not just cardiovascular mortality, was investigated in this review. This could have resulted in the merging of data that is perhaps not like-for-like, and therefore not suitable for consolidation. Doing so, could have downplayed the beneficial results that may have been observed in such healthy individuals.
Secondly, the type of omega-3 supplements within the included studies were not standardised, meaning that results of studies using different sources, proportions of EPA and DHA as well as dosages were again combined, potentially further contributing to the amalgamation of unequal data.
Another aspect overlooked was the quality of the research based on study design. The only aspect of quality considered was the presence of bias, with 25 of the 79 studies included deemed ‘reliable’ and at a low risk of bias. However, of this 25, only 2 thirds of these studies were conducted within the last 10 years. Additionally, one study included within this review had a participant size of just 11 people, making this more of a pilot study than a reliable randomised control trial. Other factors which were also not considered include genetics, digestion and the differences in the diets and lifestyles of the participants.
Furthermore, the placebos used within the studies could have also had a significant impact on results, with placebos such as olive oil being used, which can also have health benefits. Other placebos such as Aspirin, Sertraline, statins and paraffin oil were also used, providing further reasons why differences in research groups may not have been observed.
It’s also important to note the plethora of research that has demonstrated the beneficial effects of increased omega-3 intake, as well as the studies which are currently being conducted. Of the studies initially identified, 27 of these were excluded as they were currently ongoing. It could therefore be possible that had this review taken place later on, once the results of these studies had been published, the outcome may have perhaps been different. In fact there are four further very large trials in the US due to publish in the next two years which may offer further clarity.
So are fish oils no use for heart disease? We feel that this review is not as conclusive as the media presented it and that it raised more questions than gave answers. For now, we should continue to encourage increasing omega-3 intake, in line with current advice, whether this is via food sources or supplementation.
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[i] . Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2018, Issue 7. Art. No.: CD003177. http://cochranelibrary-wiley.com/doi/10.1002/14651858.CD003177.pub3/full