Dueling reports about omega-3 fats


This week’s New England Journal of Medicine (NEJM) has dueling reports about the possible benefit of omega-3 fats present in seafood. (1-4) During the past 10 years the number of people taking fish oil supplements has increased by a factor of 10. This is part of a general craze whereby more than half of us are taking some kind of dietary supplements, none of which have been shown to do any good. In the case of fish oils this is because of earlier observational reports that people who eat fish have fewer heart attacks and strokes. But more recent studies comparing the taking of fish oil supplements including one in this NEJM issue show that it doesn’t prevent cardiovascular disease or death when compared with placebo in carefully masked prospective studies. More evidence that observational studies that just watch free-range humans are less than definitive.

Fish oils have of cocktail of different omega-3 fats that are generally credited as working because of their omega-3ness. But this issue of NEJM has another report that used one particular omega-3 fat, called eicosapentanoic acid (EPA). They showed that EPA supplements did indeed cause about a 25% reduction of in death and disease from cardiovascular stuff but not death overall in 8179 people who already had CV disease or risk factors for it.

So what gives? There must be something special about this one omega-3 component of marine fish oils.

Generally it was felt that if fish oils did anything it was because of reducing your blood triglyceride levels. Remember that in the hierarchy of your lipid profile (LDL cholesterol (bad cholesterol), HDL (good cholesterol) and triglycerides) the triglycerides are the least important culprit in CV disease. In this study the levels of triglycerides didn’t seem to correlate with the benefit of the EPA. So if EPA helps anything it must be for some other reasons.

By the way vitamin D supplements, another item in the supplement craze, don’t help CV disease either and neither did vitamin D or fish oils prevent cancer.

This is good because we seem to have almost depleted the oceans of fish to eat.

1. Manson JAE. et al. Marine n-3 fatty acids and prevention of cardiovascular disease and cancer. N Engl J Med 2019;380:23-32.

2. Bhatt DL. et al. Cardiovascular risk reduction with eicosapent ethyl for hypertriglyceridemia. N Engl J Med 2019;380:11-22.

3. Kastellein JJ, AStroes ESG. FISHing for the miracle of eicosapentinoic acid. N Engl J Med 2019;380:89-90.

4. Keaney JF, Rosen CJ. Vital signs for dietary supplementation to prevent cancer and heart disease. N Engl J Med 2019;380:91-3.

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