Flogging fish oil supplements is a lucrative business. In the US alone, 19m people take the pills, spending around US$1.2 billion annually on them. Initial studies suggested that this was money well spent. Omega-3 fatty acids were shown to help maintain a healthy heart. However, a few recent studies seem to contradict this. Does that mean omega-3 fish oil supplements are a waste of money? Let’s take a closer look at the evidence.
Omega-3 fatty acids are a group of essential polyunsaturated fatty acids. They are called “essential” because we need them to function but our bodies can’t make them. We rely on sources such as fish and shellfish, or supplements, to get enough. The supplements usually contain two important types of omega-3: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
Evidence from early clinical trials demonstrated that omega-3 fatty acid supplements can reduce the risk of cardiovascular disease. In 2002, an analysis of data from the GISSI Prevenzione trial showed that omega-3 fatty acids reduce the risks of further harm in people who’d had a heart attack.
The researchers randomly assigned around 11,000 people who’d had a heart attack to 1g a day of omega-3 fatty acids or a placebo for three-and-a-half years. Compared with those assigned to take a placebo, people who took the omega-3 supplement had a 20% reduced risk of death in the follow-up period, a 15% reduced risk of non-fatal heart attack, a 30% reduced risk of cardiovascular death and a 45% reduced risk of sudden cardiac death.
And, in 2007, a large Japanese study, involving nearly 19,000 participants, showed that omega-3 fatty acids caused risk reductions of 19% in major cardiovascular events, such as heart attack and stroke.
More recently (2016), researchers at Stanford University analysed the data from 19 studies that included nearly 46,000 people from 16 countries. Over time, 7,973 participants experienced their first heart attack, of which 2,781 died as a result. The researchers found that people who had higher concentrations of omega-3 in their blood were about 10% less likely to die from a heart attack compared with people who had lower omega-3 concentrations.
Another recent study (2016) showed that omega-3 fatty acids help heart muscles recover following a heart attack. Researchers at Harvard Medical School found that, compared with those taking a placebo, participants taking a high dose of prescription-quality omega-3 fatty acids (4g daily), for six months, had less scarring on their heart muscle and an increased ability to pump blood. The study also found that the more omega-3 that was absorbed in the body, the better the heart was at pumping.
Recent trials look less certain
However, not all trials looking at the benefit of fish oil supplements on heart health have shown positive results. Several reasons for these negative findings have been proposed, including short treatment periods, relatively low doses of omega-3 fatty acids, small sample sizes (“underpowered” studies as they are called) and the concurrent use of drugs to prevent cardiovascular disease, such as statins.
Olive oil, which helps prevent cardiovascular disease, was used as a placebo in some of the clinical trials that showed no additional beneficial effect of omega-3 on heart health. In all of the trials that showed no benefit of omega-3 fatty acids, only a small amount of omega-3 fish oils (380–840mg) was used, whereas the current recommendation (which is being used in large ongoing clinical trials) is 2-4g daily.
So the negative findings in those trials doesn’t necessarily prove that omega-3 fatty acids are ineffective at preventing cardiovascular disease – they only demonstrate that they were not effective in the context in which they were being tested.
Two large ongoing clinical trials using high-dose prescription-strength omega-3 fatty acids are examining the heart benefits of omega-3 supplementation in generally healthy, low-risk groups, as well as high-risk groups around the world. The results of the REDUCE-IT trial will be available in 2018 and the STRENGTH trial will be completed closer to 2020. I’m convinced that they will provide further evidence that omega-3 is beneficial for the heart, in both sick and well people.
Go to the source
Even if future trials fail to show a benefit for fish oil supplements, no harm has been done, right? After all, they are a natural supplement. Well, not quite.
The EPA and DHA used in clinical trials was of prescription purity and strength. But with the lack of regulation of dietary supplements, many omega-3 capsules do not include all the nutrients they claim to and are sometimes loaded with extra saturated fats. Some are even contaminated with levels of carcinogens that exceed US Environmental Protection Agency standards. EPA and DHA levels can also vary widely within and between brands, with many only containing half of the EPA and DHA amounts stated on the label.
Omega-3s are highly vulnerable to breakdown during manufacturing and become oxidised (rancid) during transportation and storage. Once they are broken down, they don’t have their favourable benefits any more and, in fact, are toxic. Earlier this year, a study from Harvard Medical School revealed that three popular US brands of omega-3 fish oil supplements contained highly oxidised products that exceeded maximum levels set by international standards of quality.
Unlike buying a piece of salmon in a shop where you can smell and examine the product for freshness, you cannot do this with a bottle of fish oil supplements. Anyone wishing to top up on this healthy fatty acid would be advised to get their daily dose from the fishmongers, not the pharmacy.