Oily fish and CHD

The omega-3 fatty acids are long-chain polyunsaturated fatty acids. The parent fatty acid of this group is alpha-linolenic acid. This is an essential fatty acid that the body is unable to synthesise. In the human body linolenic acid can be converted to eicosapentaenoic acid (EPA) and docosahexaaenoic acid (DHA). Extracted fish oils and oily fish contain high levels of EPA and DHA. These compounds have been shown to decrease the production of compounds involved in thrombosis and inflammation. Fish oils also contain vitamin A and vitamin D.

• there is evidence that the consumption of one portion of fish per week (preferably oily) probably reduces the risk of coronary heart disease
  
  
• a randomised controlled trial involving 2,033 men who had recovered from a myocardial infarction found that advising men to eat oily fish led to a reduction in 2-year all-cause mortality of 29% compared to those not so advised (2)
  
  
• also there is evidence that fish oil supplements probably do help patients with some inflammatory disorders such as rheumatoid arthritis and psoriasis. Also fish oil supplements are an effective treatment of hypertriglyceridaemia
  
  
• a systematic review concluded that the evidence supports a role for fish oil or fish in secondary prevention, because the clinical trials have demonstrated a reduction in total mortality, CHD death, and sudden death (3)
  
  
• a prospective randomised controlled trial (JELIS) was undertaken in Japanes patients and suggested benefit for use of omega 3 fatty acids in reducing the risk of cardiovascular disease (4):
  • 18 645 patients with a total cholesterol of 6.5 mmol/L or greater were recruited from local physicians throughout Japan between 1996 and 1999. Patients were randomly assigned to receive either 1800 mg of eicosapentaenoic acid (EPA) daily with statin (EPA group; n=9326) or statin only (controls; n=9319) with a 5-year follow-up
  • at mean follow-up of 4.6 years, we detected the primary endpoint in 262 (2.8%) patients in the EPA group and 324 (3.5%) in controls-a 19% relative reduction in major coronary events (p=0.011)
    • post-treatment LDL cholesterol concentrations decreased 25%, from 4.7 mmol/L in both groups. Serum LDL cholesterol was not a significant factor in a reduction of risk for major coronary events
    • in patients with a history of coronary artery disease who were given EPA treatment, major coronary events we. re reduced by 19% (secondary prevention subgroup: 158 [8.7%] in the EPA group vs 197 [10.7%] in the control group; p=0.048)
    • in patients with no history of coronary artery disease, EPA treatment reduced major coronary events by 18%, but this finding was not significant (104 [1.4%] in the EPA group vs 127 [1.7%] in the control group; p=0.132)
    • the authors concluded that EPA is a promising treatment for prevention of major coronary events, and especially non-fatal coronary events, in Japanese hypercholesterolaemic patients
      
      
• the Reduction of Cardiovascular Events with Icosapent Ethyl-Intervention Trial (REDUCE-IT), has shown reduction in cardiovascular risk in patients using fish oil based supplements (5):
  • in 8179 high-risk patients who had elevated triglyceride levels and had been receiving statin therapy were randomly assigned to receive 2 g of icosapent ethyl (icosapent ethyl or ethyl eicosapentaenoic acid is a synthetic derivative of the omega-3 fatty acid eicosapentaenoic acid) twice daily or placebo containing mineral oil
  • patients were enrolled mostly on the basis of secondary prevention (71%), and almost 60% had diabetes
  • at baseline
    • low-density lipoprotein (LDL) cholesterol levels were well controlled among the patients (median value,1.94 mmol per liter [75.0 mg per deciliter]), and triglyceride levels were slightly elevated (median value, 2.44 mmol per liter, [216.0mg per deciliter])
  • after a median follow-up of 4.9 years
    • the primary efficacy end point (a composite of cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, coronary revascularization, or unstable angina in a time-to-event analysis) was reported in 22.0% of the patients in the placebo group and in 17.2% of the patients in the icosapent ethyl group - a 25% lower risk in the icosapent ethyl group

A systematic review was undertaken (7):

• to investigate the premise that mega-3 polyunsaturated fatty acids from oily fish (long-chain omega-3 (LCn3)), including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)), as well as from plants (alpha-linolenic acid (ALA)) may benefit cardiovascular health
  
  
• as systematic review was undertaken to assess the effects of increased intake of fish- and plant-based omega-3 fats for all-cause mortality, cardiovascular events, adiposity and lipids
  
  • Moderate- and low-certainty evidence suggests that increasing LCn3 slightly reduces risk of coronary heart disease mortality and events, and reduces serum triglycerides
    (evidence mainly from supplement trials). Increasing ALA slightly reduces risk of cardiovascular events and arrhythmia

Reference:

• Drug and Therapeutics Bulletin 1996; 34 (8): 60-62.
• Burr ML et al. Effects of changes in fat, fish, and fibre intakes on death and myocardial infarction: diet and infarction trial (DART). Lancet 1989; 2: 757-61.
• Harper CR et al. Usefulness of omega-3 fatty acids and the prevention of coronary heart disease. Am J Cardiol 2005; 96:1521-9.
• Yokoyama M et al. Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis. Lancet. 2007 Mar 31;369(9567):1090-8
• Bhart DL et al. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia.N Engl J Med. 2018 Nov 10
• (7) Abdelhamid AS et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2020, Issue 3. Art. No.: CD003177. DOI: 10.1002/14651858.CD003177.pub5