A review of 20 studies covering nearly 70,000 participants finds no statistically significant evidence that supplementation with omega-3 polyunsaturated fatty acids (PUFAs), commonly referred to as fish oil supplements, is linked to a lower risk of heart attack, stroke, or premature death.
However, in their attempt to clarify the recent controversy surrounding the use of omega-3 supplements, the authors do not rule out the possibility that certain groups may benefit, and call for future studies to look more closely at this.
Evangelos Rizos, of the University Hospital of Ioannina, Ioannina, Greece, and colleagues write about their findings in the 12 September issue of JAMA.
Omega-3 PUFAs are considered essential for healthy development of the heart and other parts of the body, and food sources rich in these include nuts and seeds, and oily fish such as salmon, mackerel, herring and sardines. As supplements they are typically given in the form of fish oil.
Although it is not clear how they help the heart and circulation, there are suggestions omega-3 PUFAs lower triglyceride levels, prevent serious arrythmias, reduce the clumping of platelets, and lower blood pressure.
However, the authors write that:
“Considerable controversy exists regarding the association of omega-3 polyunsaturated fatty acids (PUFAs) and major cardiovascular end points.”
Although some randomized studies suggest omega-3 PUFAs prevent heart disease, others refute this, they explain, noting also that many medical and health societies support their use for patients after heart attack (MI, myocardial infarction), either as supplements or through dietary advice.
Regulatory authorities also appear to have different views. The US Food and Drug Administration (FDA) has approved the use of omega-3 PUFAs only for lowering triglycerides in patients with overt hypertriglyceridemia, while some, but not all, European regulators have approved them for reducing cardiovascular risk.
“The controversy stemming from the varying labeling indications causes confusion in everyday clinical practice about whether to use these agents for cardiovascular protection,” write Rizos and colleagues.
Thus, in an attempt to clarify the situation, they carried out a large-scale statistical review of the available evidence from randomized controlled studies, looking at the link between omega-3 PUFAs and major cardiovascular outcomes such as stroke and heart attacks, and also premature death.
From a search of the well-known databases, they found 3,635 studies, from which 20 matched their criteria. These provided data for a pooled analysis on 68,680 randomized patients, and events that included 7,044 deaths, 3,993 cardiac deaths, 1,150 sudden deaths, 1,837 heart attacks, and 1,490 strokes.
Taking all the included supplement studies together, the researchers found no significant association between use of omega-3 PUFAs and all-cause mortality, cardiac death, sudden death, heart attack (MI), and stroke.
“… omega-3 PUFAs are not statistically significantly associated with major cardiovascular outcomes across various patient populations.”
They suggest their findings “do not justify the use of omega-3 as a structured intervention in everyday clinical practice or guidelines supporting dietary omega-3 PUFA administration.”
However, they also note that as scientists continue to do more randomized studies in this field, it would be useful to do some that look more closely at how these supplements might benefit individual risk groups, and use more refined measures such as dose, adherence and baseline intake.
In other words, while looking at all the evidence as a whole does not appear to support the idea that omega-3 PUFA supplements benefit the heart, this broad-brush picture could be missing details: there may be certain groups that do benefit, and this may also depend on factors such as the supplement dose and how long they take it for.
In comments made to Medical News Today, the National Lipid Association have said that they do not necessarily agree with the conclusions reached by the review:
“In this study, the authors used P value of 0.006 corrected for multiple comparisons without clear details or citation for the rationale. If the authors had used the standard criterion (P value of 0.05) or would have been more transparent as to why they used the stricter criterion, then the conclusion would have been easier to interpret. The NLA believes that this review is not conclusive yet we remain open to further looks at this challenging question.
The National Lipid Association continues to believe that the totality of published evidence supports the use of both fish and fish oil supplementation to reduce the risk for cardiovascular disease and that this paper does not alter that perspective. As always, patients should consult with their health care provider before stopping or starting any medication or dietary supplement.”
Some other recent individual studies, published in Medical News Today, have also concluded that fish oils do not appear to provide some of the benefits people had previously taken for granted. Researchers from the London School of Hygiene & Tropical Medicine found that taking omega-3 fish oil supplements appears not to protect older people from cognitive decline.
In contrast, a study published on September 10th found that DHA intake may help improve reading and behavior in healthy but underperforming children. DHA is an omega-3 fatty acid. You can look up other studies related to omega-3 fish oils in our archive.
Written by Catharine Paddock PhD
Article updated: 24 September 2012.