We’ve long been told fish oil promotes bleeding, and to stop taking omega-3s before surgery.
You never know when you might land in emergency surgery.
And when you go under the knife, it’s critical to keep bleeding under control.
Concerns center on anticoagulant “blood thinning” drugs like Coumadin (warfarin) and several arguably superior modern counterparts such as Eliquis, Pradaxa, and Xarelto.
For decades, doctors have advised — or ordered — their patients to stop taking fish oil well before surgery, out of concern for its ability to thin blood.
Omega-3s certainly do discourage unhealthful “stickiness” among blood platelets, which helps cardiovascular health.
But do the omega-3s found in human cells and in seafood (DHA and EPA) really produce bleeding risks like those associated with pharmaceutical anticoagulants?
Danish researchers just published a comprehensive evidence review of studies about fish oil’s effects on bleeding times.
Coincidentally, Canadian researchers recently reviewed the evidence about the effects of omega-3 fish oil on surgery outcomes.
Before we scrutinize both studies, let's examine the story that led to fears about taking fish oil before surgery.
Greenland Eskimo study raised first bleeding-time fears
Bleeding time is the time it takes for your blood to coagulate when you receive a cut, whether accidental or surgical.
Fears about fish oil's effects on bleeding time during surgery stemmed from a 1975 Danish study in Greenland Eskimos.
The Greenland Eskimos ate diets very high in omega-3s from seafood, with omega-3 blood levels seven to 13 times higher than average European or American levels.
While they had superior heart health, they also displayed much longer “bleeding times” than average Americans or Europeans.
Finding in Alaskan Eskimos challenged fish oil fears
A 1994 study in Alaskan Eskimos directly challenged the idea that the Greenland Eskimos’ high omega-3 levels were responsible for their long bleeding times.
Although the Alaskan Eskimos had comparably high blood levels of omega-3s, their bleeding times were more like those seen in average Americans or Europeans.
And, compared with their Greenland counterparts, the Alaskan Eskimos had much higher blood levels of omega-6 AA — which mainly comes from meats and dairy — like the AA levels seen in average Americans or Europeans.
That difference in omega-6 AA blood levels may explain why average bleeding times among Alaskan Eskimos were much shorter than average bleeding times among Greenland Eskimos.
Regardless of the reason, it no longer made sense to place blame for the Greenland Eskimos' long bleeding times on their high omega-3 levels.
But few doctors were aware of the contradictory finding in Alaskan Eskimos, good studies on fish oil and bleeding times were lacking, and evidence that fish oil can aid surgical recovery only arrived in recent years.
Recent evidence review finds no backing for fish oil fears
The first well-publicized challenge to fears about fish oil arrived in 2008, when prominent cardiac researcher William S. Harris, Ph.D., reported that he could find no supporting evidence (see Can Fish Oil Cause Bleeding Risks?).
Now, researchers at Denmark’s Aarhus University Hospital have published another evidence review, which should put the old fish oil fears to rest.
After examining 16 studies in patients undergoing heart surgery, the Danish team concluded that taking fish oil before surgery did not increase bleeding or the required amount of transfused blood (Begtrup KM et al. 2017).
They also reviewed evidence from 32 studies in healthy people, which confirmed that fish oil supplementation reduces platelet aggregation — an effect that could possibly lengthen bleeding time.
The Danes highlighted the apparently contradictory outcomes of both reviews:
“As the biochemical effect of fish oil supplements in healthy subjects was not reflected in an increased bleeding risk during surgery, this systematic review does not support the need for discontinuation of fish oil supplements prior to surgery or other invasive procedures.”
Fish oil may shorten hospital stays for heart-surgery patients
Ten years back, we covered encouraging findings about the effects of fish oil in cancer-surgery patients … see Omega-3s May Enhance Post-Surgery Outcomes.
And earlier this month, scientists at Canada’s Sherbrooke University published the encouraging results of their review of evidence from studies in heart surgery patients.
The Canadian team scrutinized 19 randomized, controlled clinical trials that had collected data on the length of hospital stays and the risk of risky heart rhythms (atrial fibrillation) after heart surgery (Langlois PL et al. 2017).
In each case, the authors of the original studies had collected information about the patient’s use of supplements, including fish oil.
Most previous evidence reviews had only examined the effect of pre-surgery fish oil supplements on risky post-operative atrial fibrillation (POAF) — with mixed findings — rather than clinical outcomes such as length of hospital stay (LOS).
Importantly, the authors of the new review found that patients who’d been taking fish oil before surgery spent 1.4 fewer days in the hospital, and enjoyed a 22% lower rate of POAF.
As the Canadians wrote, “This updated systematic review and meta-analysis demonstrates that [fish oil] administered to patients undergoing cardiac surgery may be able to significantly reduce hospital LOS and the incidence of POAF.”
The Quebec-based researchers noted that patients undergoing open-heart surgery showed the most significant reductions in inflammation and rates of atrial fibrillation.
Their review found no evidence for other significant advantages among patients who took fish oil in the weeks or months before surgery, such as length of stay in intensive care units or risk of death after surgery.
Lead researcher Pascal Langlois said the findings should encourage more research on the possible benefits of taking omega-3 fish oil before heart surgery, and lay bleeding fears to rest.
Interestingly, recent studies from China and Iran found that taking omega-3 fish oil and vitamin C before surgery may produce even better outcomes (Guo XY et al. 2014; Ali-Hassan-Sayegh S et al. 2014).
Clearly, it's time to stop worrying that a daily regimen of fish oil will pose a bleeding risk during surgery.
Instead, it looks like fish oil eases recovery from surgery, and should be encouraged for that reason among many others.
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