Figure 1: According to a study of over 400,000 participants, taking fish oil supplements may increase the risk of cardiovascular disease in healthy people.
Many people regularly take fish oil supplements to ensure they meet their omega-3 requirements. Omega-3 fatty acids are essential and are thought, among other things, to protect against cardiovascular disease. However, a British study has now concluded that fish oil can, in certain cases, even harm heart health. In this blog article you will learn why the study has caused an international stir and whether you can continue to take fish oil supplements without concern.
Why do we need omega-3 fatty acids?
Before we turn to the much-discussed study on fish oil supplementation, it should be clarified what we actually need omega-3 fatty acids for. Because the body cannot produce them itself, omega-3 fatty acids must be obtained from the diet. These polyunsaturated fatty acids fulfil many vital functions in the body. Among other things, they play a central role in hormone production, the regulation of blood lipid levels, protein synthesis and cellular metabolism.
A distinction is generally made between short-chain and long-chain omega-3 fatty acids. The short-chain alpha-linolenic acid (ALA) is found, among other sources, in flaxseed, hemp and chia seeds and in oils derived from those seeds. The best-known long-chain omega-3 fatty acids are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These can be produced by the body from ALA to a limited extent. They are also present in oily marine fish such as mackerel, herring, tuna and salmon. Those who follow a vegetarian or vegan diet can obtain EPA and DHA from microalgae or by supplementing with algal oil.
Study from the UK: Is fish oil really harmful?
Whether supplementation with omega-3 fatty acids is helpful in heart disease has long been a matter of controversy. Recently, a paper published in the journal BMJ rekindled the debate. [1] The large cohort study was conducted by a research team made up of Chinese, American, British and Danish scientists.
Over almost twelve years, data from a total of 415,737 participants in a British bio-database were collected and then analysed by the researchers. Hospital records and death registries provided information on deaths and cardiac events that had occurred. At the start of the study, participants were between 40 and 69 years old. As recorded in a questionnaire, about one third of the subjects regularly took fish oil supplements.
Now for the results: the data analysis showed that regular use of fish oil supplements increased the participants' risk of atrial fibrillation by 13 percent and their risk of stroke by 5 percent. Other health risks, however, such as the progression from atrial fibrillation to myocardial infarction or from heart failure to death, could be reduced by fish oil supplementation by 15 percent and 9 percent respectively.
People with heart disease may benefit from fish oil supplements
Interestingly, the results described above applied only to the subgroup of participants who were heart-healthy at the start of the study. Participants who already had a known cardiovascular disease at baseline tended to benefit from regular use of fish oil supplements. The omega-3 fatty acids in fish oil reduced the risk of progression from atrial fibrillation to a serious cardiovascular event by 8 percent. The risk of progression from atrial fibrillation to a heart attack fell by as much as 15 percent; the risk of progression from heart failure to death by 9 percent.
These positive effects of fish oil intake were even more pronounced in older people and in men. The risk of a progression from a heart-healthy state to death due to a cardiovascular event was reduced by fish oil supplements by 11 percent (in older people) and by 7 percent (in men).
Relevance and limitations of the study
Although the British study on fish oil supplements has rightly received much attention in the press, there are several points to consider when interpreting the results. Because it was a purely observational study, associations can be described but no definitive causal relationships between supplementation and heart disease can be established.
In the questionnaire filled in by participants at baseline, participants were only asked whether they took fish oil as a dietary supplement. Which products were used, in what dosages and compositions, was not known to the researchers. The study results also relate only to omega-3 supplements. Whether the consumption of fish with a high omega-3 content brings similar benefits and risks remains unanswered.
What other studies say about omega-3 supplementation
Figure 2: The evidence on omega-3 supplements in relation to cardiovascular disease is inconclusive and at times contradictory.
As noted at the outset, the effectiveness of omega-3 supplements for cardiovascular disease has often been questioned. To date, there is no study that unequivocally demonstrates that omega-3 supplementation can reduce the risk of serious cardiovascular events such as heart attack, stroke or heart failure equally in all people.
A review that evaluated a large number of medical studies on the relationship between fish oil and cardiovascular disease also emphasises that further randomised and controlled trials are needed to examine the effects of EPA, DHA or an optimal combination of these two omega-3 fatty acids on the cardiovascular system. [2]
A Chinese meta-analysis [3] likewise emphasises that the potential positive effects of omega-3 fatty acids in the treatment and prevention of coronary heart disease require further research. At the same time, the analysis concluded that omega-3 supplementation with a daily dose of 0.8 to 1.2 grams of omega-3 fatty acids can reduce the risk of cardiovascular-related deaths, heart attacks and so-called MACE ("major adverse cardiac events").
Is the dose important?
When it comes to omega-3 fatty acids, a dosage that takes the individual's health status into account appears to be crucial. Omega-3 fatty acids are essential and should therefore be supplied in sufficient amounts. However, the dose should not be too high, as an overdose can increase bleeding tendency, alter the flow properties of the blood and prolong bleeding time. People who are already taking anticoagulant medication should therefore be particularly cautious and only take supplements such as fish oil capsules after consulting a doctor.
Due to the controversial and inconclusive state of research on omega-3 fatty acids, dosing recommendations also vary considerably. According to an opinion of the European Food Safety Authority (EFSA), an additional daily intake of up to 5 grams of EPA/DHA (combined) and up to 1.8 grams of EPA (alone) is considered safe. [4] The German Federal Institute for Risk Assessment (BfR), on the other hand, recommends not taking more than 1.5 grams of unsaturated omega-3 fatty acids per day from all sources (food as well as any dietary supplements). [5]
Conclusion: Is it sensible to supplement fish oil?
It is understandable that the BMJ-published study has unsettled people who regularly take fish oil supplements. However, as Nathan Davies, a nutrition scientist at University College London, emphasises, the study results are not a reason to stop an ongoing omega-3 supplementation. Those who tolerate the supplements well and benefit from them can continue taking them without problems.
At the same time, Davies points out that omega-3 requirements can generally be met through a balanced and varied diet. The German Nutrition Society (DGE) recommends eating one to two portions of fish per week. Depending on the fish species chosen, this already provides 250 milligrams of EPA and DHA. According to the DGE, this amount is necessary to help prevent deaths caused by coronary heart disease. [6]
If you choose to avoid eating fish or taking fish oil for ecological, taste or health reasons, you can alternatively turn to microalgae. DHA-rich microalgal oils from species such as Schizochytrium or Ulkenia can be useful as a dietary supplement to meet omega-3 requirements.
Sources:
[1] Chen, G., Qian, Z., Zhang, J. et al. Regular use of fish oil supplements and course of cardiovascular diseases: prospective cohort study. BMJ Medicine 2024. https://bmjmedicine.bmj.com/content/3/1/e000451 (accessed: 05.06.2024).
[2] Liao, J., Xiong, Q., Yin, Y., et al. The Effects of Fish Oil on Cardiovascular Diseases: Systematical Evaluation and Recent Advance. Frontiers in Cardiovascular Medicine, Volume 8, 2022. https://www.frontiersin.org/articles/10.3389/fcvm.2021.802306/full (accessed: 05.06.2024).
[3] ShiChun, S., Chen, G., KaiQin, J., et al. Omega-3 Fatty Acid Supplementation and Coronary Heart Disease Risks: A Meta-Analysis of Randomized Controlled Clinical Trials. Frontiers in Nutrition, Volume 9, 2022. https://www.frontiersin.org/articles/10.3389/fnut.2022.809311/full (accessed: 05.06.2024).
[4] EFSA (2012): EFSA assesses the safety of long-chain omega-3 fatty acids. https://www.efsa.europa.eu/de/press/news/120727 (accessed: 05.06.2024).
[5] BfR (2009): For the fortification of foods with omega-3 fatty acids, the BfR recommends setting maximum amounts. https://www.bfr.bund.de/cm/343/fuer_die_anreicherung_von_lebensmitteln_mit_omega_3_fettsaeuren_empfiehlt_das_bfr_die_festsetzung_von_hoechstmengen.pdf (accessed: 05.06.2024).
[6] DGE (2018): Regular fish on the table! https://www.dge.de/presse/meldungen/2011-2018/weniger-fleisch-auf-dem-teller-schont-das-klima/dge-empfiehlt-auf-fettmenge-und-qualitaet-achten/regelmaessig-fisch-auf-den-tisch/ (accessed: 05.06.2024).
Photos: Unsplash: Ishaq Robin, Joshua Earle
