The various enzymes (COX and LOX) that make inflammatory eicosanoids can accommodate both AA and EPA, but again due to the greater spatial size of DHA, these enzymes will have difficulty in converting DHA into eicosanoids. This makes DHA a poor substrate for these key inflammatory enzymes. Thus DHA again has little effect on cellular inflammation whereas EPA can have a powerful impact.
Studies have also found that omega-3 fatty acids from fish oil are associated with improved survival rates for heart attack victims. A study published in the medical journal Circulation found that people who took a high dose of fish oil each for six months following the occurrence of a heart attack actually improved their hearts’ overall functioning and also reduced biomarkers of systemic inflammation. (20)
Nonetheless, large population studies with solid data both on the participants’ diets and causes of disease and death bolstered the beliefs that eating fish often was a heart-healthy practice linked to reduced rates of cardiovascular disease. For example, a comprehensive analysis conducted by Dr. Dariush Mozaffarian and Eric Rimm of the Harvard T.H. Chan School of Public Health found that eating two servings of fatty fish a week — equal to about two grams of omega-3 fatty acids — lowered the risk of death from heart disease by more than a third and total deaths by 17 percent.
The omega-3 index is also important because it is inversely related to one’s omega-6 to omega-3 ratio — another important measurement (3). A lower omega-6/omega-3 ratio (meaning, you consume a balanced amount of these two fatty acid families) is associated with a reduced risk of many chronic diseases, including cardiovascular disease, cancer, and autoimmune disease, to name a few (4). Of course, most people get far too much omega-6 and too little omega-3, thanks to the plethora of highly processed foods in the Western diet.
For dry eye: Fish oil supplements providing EPA 360-1680 mg and DHA 240-560 mg have been used for 4-12 weeks. Some people used the specific product (PRN Dry Eye Omega Benefits softgels). A specific combination product containing EPA 450 mg, DHA 300 mg, and flaxseed oil 1000 mg (TheraTears Nutrition, Advanced Nutrition Research; Caruso’s Natural Health UltraMAX fish oil, Sydney, New South Wales, Australia) has been used once daily for 90 days.
“This systematic review did find moderate evidence that ALA, found in plant oils (such as rapeseed or canola oil) and nuts (particularly walnuts) may be slightly protective of some diseases of the heart and circulation. However, the effect is very small, 143 people would need to increase their ALA intake to prevent one person developing arrhythmia. One thousand people would need to increase their ALA intake to prevent one person dying of coronary heart disease or experiencing a cardiovascular event.  ALA is an essential fatty acid, an important part of a balanced diet, and increasing intakes may be slightly beneficial for prevention or treatment of cardiovascular disease."
A lot of the benefit of fish oil seems to come from the omega-3 fatty acids that it contains. Interestingly, the body does not produce its own omega-3 fatty acids. Nor can the body make omega-3 fatty acids from omega-6 fatty acids, which are common in the Western diet. A lot of research has been done on EPA and DHA, two types of omega-3 acids that are often included in fish oil supplements.
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