Omega-3 (or n-3) Fatty Acids
Part I

What Are They?

Omega-3 fatty acids are polyunsaturated fatty acids (PUFAs) found in certain fatty fish and vegetables.  There has been a significant amount of interest in the potential health benefits of increasing dietary intake of these fatty acids.  These potential benefits include:

• reduction in arrhythmias and sudden cardiac death
• reduction in triglyceride levels
• improvement in blood pressure control, certain autoimmune diseases, and depression

The best scientific evidence for potential benefit is that for reduction in arrhythmias and sudden cardiac death (summarized below), and for reduction in triglyceride levels (to be summarized in part 2).

Types and Sources of Omega-3 Fatty Acids

• Alpha-Linolenic Acid (ALA): found in land-based sources such as green plants, soybeans, flaxseed oil.
  
  
• Eicosapentanenoic Acid (EPA) and Docosahexanoic Acid (DHA): found in fatty cold water fish such as tuna, salmon, mackerel, halibut, and sardines.

Evidence of Benefit:  Reduction in Cardiac Events

Observational Studies:

CHD death from sudden death reduced by ~50% with consumption of 1-2 servings of fish per week; higher amount of intake was not associated with additional risk reduction. JAMA 1998; 279: 23; JAMA 1995; 274: 1363  

Secondary Prevention Trials:

Diet and Reinfarction Trial (DART). Lancet 1989; 334: 757

• Advice to eat fatty fish 2x/wk: 29% reduction in total mortality
  (see "Articles of further interest" below)

GISSI-Prevenzione Trial. Lancet 1999; 354: 447

• n-3 supplement of 1g/d of EPA+DHA vs. placebo:
  • 20% reduction in total mortality
  • 45% reduction in sudden death

Lyon Diet Heart Study. Lancet 1994; 343: 1454 review available at the
American Heart Association web site http://216.185.112.5/presenter.jhtml?identifier=4655

• Mediterranean diet with high content of ALA: 70% reduction in CHD events and deaths. Mediterranean Diet http://216.185.112.5/presenter.jhtml?identifier=4644

Likely Mechanism for Reduction in CHD events:

Antiarrhythmic effect of n-3 fatty acids that results in reduction of sudden death due to ventricular fibrillation and tachycardia. Am J Clin Nutr 2000; 7: 202S.

Articles of further interest:

Fish Consumption, Fish Oils, Lipids and Coronary Heart Disease
American Heart Association web site http://216.185.112.5/presenter.jhtml?identifier=1812

Fatty Fish Cuts Risk of Death From Heart Attack in the Elderly
American Heart Association web site http://216.185.112.5/presenter.jhtml?identifier=3283