A fishy relationship between omega-3 fatty acids and heart health

Introduction

In 2015^[1], 17.9 million deaths were caused by cardiovascular diseases (CVDs), which include coronary heart disease, angina, heart attacks, strokes, and heart failure. The most common age group to suffer from CVD are older adults^[2] over the age of 60.

The strongest risk factors for CVD include high blood pressure, high cholesterol, smoking, diabetes, lack of physical activity, obesity, and poor nutrition. Thus, many events that result from CVD are largely preventable^[3] through lifestyle. When it comes to nutrition, government agencies and organizations have promoted the consumption of unrefined plants and discouraged excessive consumption of foods and drinks high in fats, sugars, salt, and alcohol.

Fish and fish oil consumption, in particular, has a long history linking it to CVD prevention, which is summarized in Figure 1. The story started, in part, due to observational evidence^[4] suggesting that fish consumption was associated with a reduced risk of cardiovascular disease, which led to randomized trials investigating the effects of fish oil on CVD outcomes.

Figure 1: A brief review of the history of fish oil
1970s	Researchers saw that a group of people^[4] who ate fish had a lower incidence of CVD.
1980s–1990s	Early studies^[5]^[6] found associations between fish consumption and heart disease risk.
1990s	Randomized trials^[7]^[8] were conducted to see the effects of fish oil on CVD outcomes.
2002	The American Heart Association puts out a statement^[9] explaining that fish oil supplementation was protective with regards to fatal outcomes.
2002–2016	More randomized trials^[10]^[11] and systematic reviews produced inconsistent results.
2016	The American Heart Association forms a scientific advisory group^[12] to synthesize and analyze all the available evidence and concludes that there was a small benefit from fish oil for people who had a history of CVD events.
2018	Large meta-analysis^[13] published in JAMA with 77,000 + participants found no benefit from fish oil supplementation on real clinical endpoints.

In 2002, the American Heart Association (AHA) put out a statement^[14] discussing the available randomized controlled trials (RCTs) at the time and concluded that eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) supplements significantly reduced fatal cardiac events.

Several RCTs^[11] conducted after this statement found conflicting evidence of fish oil supplementation improving fatal or even nonfatal CVD outcomes. In 2016^[12], the AHA formed an advisory group to perform another review of all the RCTs available at the time and concluded that despite there being controversial evidence, the AHA believed that fish oil supplementation was beneficial for people who recently experienced a cardiac event.

However, this review performed by the AHA was not a quantitative analysis of all the published data. The meta-analysis under review decided to look at the largest controlled trials published to objectively review the relationship between fish oil supplementation and CVD outcomes and to end the confusion around fish oil.

CVD is the leading cause of death worldwide and is sometimes preventable through lifestyle changes. Several researchers and organizations have been interested in the effects of fish oil on CVD outcomes but have found conflicting evidence. The meta-analysis under review re-evaluated some of the largest trials on the topic, and assessed the relationship between fish oil supplementation and CVD outcomes.

Who and what was studied

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