Many studies on this nutrient make it challenging to know whether supplements help heart health.
A recent meta-analysis looked at only the most extensive randomized trials and found no benefit.
In 2015, millions of deaths were caused by cardiovascular diseases (CVD).
These diseases include:
- Coronary heart disease.
- Heart attacks.
- Cerebrovascular accidents.
- Heart failure .
The most common age group to suffer from CVD is older adults over 60 years.
The most substantial risk factors for CVD include:
- High blood pressure.
- High cholesterol.
- Lack of physical activity.
- Bad nutrition.
Therefore, many events that result from CVD are largely preventable 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 beverages high in fat, sugar, salt, and alcohol.
The consumption of fish and fish oil, in particular, has a long history that links it to CVD prevention.
The story began, in part, because of observational evidence suggesting that fish consumption was associated with a lower risk of cardiovascular disease, leading to randomized trials investigating the effects of fish oil on CVD outcomes.
In 2002, a statement on the currently available randomized controlled trials (RCTs) was published and concluded that eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) significantly supplemented reduced fatal cardiac events.
Several RCTs conducted after this statement found conflicting evidence of fish oil supplementation improving fatal or even non-fatal CVD outcomes.
In 2016, another review of all available RCTs was carried out and concluded that Fish oil supplementation is believed to be beneficial for people who have recently experienced a cardiac event despite controversial evidence.
However, this review was not a quantitative analysis of all published data.
The meta-analysis under review decided to look at the most extensive published controlled trials to objectively review the relationship between fish oil supplements and CVD outcomes and end the confusion around fish oil.
Cardiovascular disease is the leading cause of death worldwide and can sometimes be prevented through lifestyle changes.
Various researchers and organizations have been interested in the effects of fish oil on CVD results but have found conflicting evidence.
The meta-analysis under review re-evaluated some of the more extensive trials on the topic and assessed the relationship between fish oil supplementation and CVD outcomes.
Who and what was studied?
This meta-analysis was conducted to quantify the effects of omega-3 fatty acid supplementation on coronary heart disease (CAD), non-fatal heart attacks, strokes, major vascular events, and all-cause mortality.
For a clinical trial to be included, you must compare omega-3 supplements to control, it must have a minimum of 500 participants, and it must be at least one year long.
A review included ten trials with 77,917 participants, with sample sizes ranging from 563 to 18,645 participants in individual trials.
The average age of the participants was 64 years, and 61.4% (47,803) of them were men. Almost two-thirds of the participants had a medical history of coronary heart disease, a third had a prior stroke, and more than a third had a history of diabetes.
The average duration of the included trials was 4.4 years, with individual trial lengths ranging from one to six years.
Of the ten trials, eight were double-blind, placebo-controlled trials, and two were open-label, where participants knew what treatment they were receiving.
Most of the trials were at low risk of bias, which are systematic errors leading to inaccurate results. For example, open-label studies had a higher chance of discrimination because they were not blinded.
Nine of the trials used a combination of EPA and DHA supplements, while one used a high-dose EPA supplement. The doses of EPA used in the trials ranged from 226 to 1800 milligrams per day, and DHA went from zero to 1700 milligrams per day.
Subgroup analyzes (specified in the pre-registration protocol) were performed to determine associations between primary outcomes and variables such as:
- CHD Previa.
- Stroke previo.
- Previous diabetes.
- Lipids in blood.
- Prior use of statins.
- Test design (open-label or blinded).
Because they were testing multiple models, the authors adjusted for multiple comparisons.
This meta-analysis of 10 randomized controlled trials included 77,917 participants and explored associations between EPA and DHA supplementation and various cardiovascular disease outcomes, such as fatal CHD, non-fatal heart attacks, stroke, and other variables over one to six years.
What were the findings?
The analysis found that omega-3 fatty acid supplementation for an average of 4.4 years had no significant effect on death from CHD, non-fatal heart attacks, stroke, revascularization events, or any major vascular event.
Subgroup analyses found no correlation between primary outcomes and variables such as age, sex, previous CAD, previous stroke, previous diabetes, blood lipids, previous statin use, and trial design (open or blind).
However, there were notable differences in effects between open-label trials and double-blind trials regarding CHD events.
There was no significant association between omega-3 FA supplementation and any primary outcomes. There was also no association between the immediate results and any of the variables explored in the subgroup analyzes.
What does the study tell us?
This large meta-analysis suggests that omega-3 fatty acid supplementation does not appear to have a beneficial effect on fatal coronary heart disease, non-fatal heart attacks, strokes, major vascular events, and all-cause mortality. Causes.
None of the combined results showed any significant association with supplementation.
One of the advantages of this meta-analysis is that it only included studies with large sample sizes, which increases the precision of the data and reduces the probability of false positives and negatives.
Furthermore, it only included studies that lasted at least a year (which gives us a clue about the long-term effects), and it only included trials that compared supplementation with some form of control. Furthermore, most of the included trials were at low risk of bias.
This is particularly important because the goal of a meta-analysis is to mimic a giant clinical trial, and larger sample sizes reduce random error (noise).
However, large sample sizes cannot reduce the impact of systematic errors (bias). Only quality control can do this. As most of the included studies were at low risk of bias, the survey results can be trusted more.
However, two of the ten included trials were open, while the rest were double-blind. This is a potential source of bias, and these two studies were also rated at a higher risk of bias than the other studies.
The results of these potentially biased studies had averages that suggested benefits but with significant standard errors and wide uncertainty intervals (which should make us less confident of the norm).