10 July 2019 Blog Post: Fish Oil

One difficulty physicians often encounter is reconciling clinical studies that reach contradictory conclusions. Just this week I have seen the following ‘conclusions’ about fish oil.
1. An impressive sounding article published by the New York Times on July 1st entitled “10 Medical Myths We Should Stop Believing. Doctors, Too.” Myth #2, in bold print, “Fish oil does not reduce the risk of heart disease.” The NYT article cites a single trial involving 12,500 people at risk for heart trouble, daily omega-3 supplements did not protect against heart disease.
2. An article published today in the Annals of Internal Medicine showed the exact opposite. This study looking at the risk of heart disease encompassed a total of 277 trials, 24 interventions, and 992,129 participants. It considered a variety of supplements and interventions (including multivitamins; vitamins A, C, and E; vitamin D alone; reduced saturated fat intake; and the Mediterranean diet). This study showed with “low-certainty” that omega-3 long-chain polyunsaturated fatty acid was associated with reduced risk for myocardial infarction (heart attack) and coronary heart disease.
So who do you believe? At first blush, a study involving nearly a 1,000,000 participants seems a lot more compelling than one involving 12,500. But sample size alone may not make it a ‘better’ study (although it certainly has more statistical power). However, these two seemingly contradictory studies may in fact be studying different things. The trial cited by the NYT is among individuals “at risk of heart trouble”. The second article considered a wider segment of the population.
So what do you do? A reasonable conclusion for the general public is that based on the evidence for effects on risk factors and clinical events, and (importantly!) no evidence to suggest harm, most adults should consume at least one to two servings per week of oily fish. Those who do not eat this much fish may consider taking a daily fish oil supplement (about 1 g/day).
Further, it seems to me that “This Week In Fish Oil” also is a cautionary tale against headlines labeling supplements or interventions as a “myth” when previous evidence was simply contradictory. It also argues against a notion of a single definitive study as compared to a broader analysis of existing information. In this case, the fish oil “myth” was instead supported with compelling evidence only 8 days later.

𝗦𝗶𝗴𝗻 𝗨𝗽 𝗳𝗼𝗿 𝗢𝘂𝗿 𝗡𝗲𝘄𝘀𝗹𝗲𝘁𝘁𝗲𝗿

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