People with cardiovascular disease who regularly ate fish had significantly fewer major CVD events and there were fewer total deaths, compared with similar individuals who didn’t eat fish, but there was no beneficial link from eating fish among the general population in prospective data collected from more than 191,000 people from 58 countries.
Despite the neutral finding among people without CVD, the finding that eating fish was associated with significant benefit for those with CVD or who were at high risk for CVD confirms the public health importance of regular fish or fish oil consumption, said one expert.
A little over a quarter of those included in the new study had a history of CVD or were at high risk for CVD. In this subgroup of more than 51,000 people, those who consumed on average at least two servings of fish weekly (at least 175 g, or about 6.2 ounces per week) had a significant 16% lower rate of major CVD events during a median follow-up of about 7.5 years.
The rate of all-cause death was a significant 18% lower among people who ate two or more fish portions weekly, compared with those who didn’t, Deepa Mohan, PhD, and associates wrote in their report in JAMA Internal Medicine.
The researchers saw no additional benefit when people regularly ate greater amounts of fish.
“There is a significant protective benefit of fish consumption in people with cardiovascular disease,” said Andrew Mente, PhD, a senior investigator on the study and an epidemiologist at McMaster University, Hamilton, Ont..
“This study has important implications for guidelines on fish intake globally. It indicates that increasing fish consumption and particularly oily fish in vascular patients may produce a modest cardiovascular benefit,” he said in a statement released by McMaster.
‘A large body of evidence’ for CVD benefit
The neutral finding of no significant benefit (as well as no harm) regarding either CVD events or total mortality among people without CVD “does not alter the large body of prior observational evidence supporting the cardiac benefits of fish intake in general populations,” noted Dariush Mozaffarian, MD, DrPH, in a commentary that accompanies the report by Dr. Mohan and colleagues.
Although the new analysis failed to show a significant association between regular fish consumption and fewer CVD events for people without established CVD or CVD risk, “based on the cumulative evidence from prospective observational studies, randomized clinical trials, and mechanistic and experimental studies, modest fish consumption appears to have some cardiac benefits,” he added.
“Adults should aim to consume about two servings of fish per week, and larger benefits may accrue from nonfried oily (dark meat) fish,” wrote Dr. Mozaffarian, a professor of medicine and nutrition at Tufts University, Boston.
Oily, dark fishes include salmon, tuna steak, mackerel, herring, and sardines. Species such as these contain the highest levels of long-chain omega-3 fatty acids, eicosapentaenoic acid, and docosapentaenoic acid; these nutrients likely underlie the CVD benefits from fish, Dr. Mozaffarian said in an interview with JAMA Internal Medicine that accompanied his commentary. (Dr. Mente also participated.)
“Fish oil lowers heart rate, blood pressure, and triglycerides (at high dosages), increases adiponectin, improves endothelial function, and in some studies improves oxygen consumption in myocardium. If there is benefit from fish it’s from the omega 3s, and all in all the evidence supports this,” but because the evidence is primarily observational, it can only show linkage and cannot prove causation, he explained.
Given the potential benefit and limited risk, “I think everyone should aim to eat two servings of fish each week, preferentially oily fish. That’s very solid,” said Dr. Mozaffarian, who is also a cardiologist and dean of the Tufts Friedman School of Nutrition Science.
The investigators did not have adequate data to compare the associations between outcomes and a diet with oily fish versus less oily fish.