Heart Disease Prevention
Studies on fish or fish oil for preventing cardiovascular disease, slowing the progression of cardiovascular disease , and preventing heart-related death have returned somewhat contradictory results. 106-125,150,156 A major review published in 2004 failed to find trustworthy evidence of benefit, 218 and a subsequent study actually found that use of fish oil increases risk of sudden death in people with stable heart disease. 219 A 2008 systematic review found that fish oil was associated with modestly reduced cardiac mortality, but not sudden cardiac death, in 11 studies totally over 32,000 patients. The reliability of these results, however, is limited by the inclusion of mostly low-to-moderate quality trials. 272 A 2009 review pooled data from 8 trials examining the effect of omega-3 fatty acids on prevention of cardiac death in almost 21,000 patients with coronary heart disease. 274 This review separated patients into two general groups (those with previous myocardial infarction versus those with angina history) and found that omega-3 supplementation reduced risk of sudden cardiac death in patients with previous myocardial infarction, but increased risk in patients with angina. Though compelling, this finding may be limited since it was derived from a retrospective analysis of original data reorganized into subgroups. Finally, a 2012 review of 14 randomized, controlled trials involving over 20,000 people further questions the supplement's value in patients with cardiovascular disease. 286 Researchers concluded that omega-3 fatty acids (ranging from 0.4-4.8 g/day) were no better than placebo at reducing rates of cardiovascular events or cardiovascular-related death.
A gigantic study (over 18,000 participants) published in 2007 was widely described in the media as finally proving beyond a shadow of a doubt that fish oil helps prevent heart problems. 239 Unfortunately, this study lacked a placebo group, and therefore failed to provide reliable evidence.
As noted earlier, fish oil is hypothesized to exert several separate effects that act together to help protect the heart. The most important action of fish oil may be its apparent ability to reduce high triglyceride levels . Like cholesterol, triglycerides are a type of fat in the blood that tends to damage the arteries, leading to heart disease. According to most, though not all studies, fish oil supplements can reduce triglycerides by as much as 25%-30%. 90-93,151,256 In a detailed review of 47 randomized trials, researchers concluded that fish oil is capable of significantly reducing triglyceride levels with no change in total cholesterol levels and only slight increases in HDL (“good”) cholesterol and LDL (“bad”) cholesterol. 268 However, in some studies, use of fish oil has markedly raised LDL cholesterol, which might offset some of the benefit. A 2009 review of 30 trials involving about 1,500 patients with type 2 diabetes demonstrated that marine-derived omega-3 polyunsaturated fatty acids (mean dose 2.4 g per day) lowered triglyceride levels about 15 mg/dL but increased LDL cholesterol by about 3 mg/dL after an average 24 weeks of treatment. 275
Fish oil has been specifically studied for reducing triglyceride levels in people with diabetes (a major risk factor for cardiovascular disease), and it appears to do so safely and effectively. 3,262 In one large trial, however, Omacor (the specially-processed, FDA-approved omega-3 product) was not found to benefit people with diabetes or prediabetes. 287 Over 12,000 such patients were randomized to receive Omacor (1 g) or placebo. All of the study participants had cardiovascular disease or had risk factors for the disease. Six years later at the follow-up, researchers found that there were no differences between the two groups in regards to cardiovascular-related death, heart attacks, strokes, or heart-related hospitalizations and surgeries. The only bright spot was that Omacor did help to reduce high triglyceride levels.
Stanols and sterols (or phytosterols) are naturally occurring substances found in various plants that can help to lower cholesterol in individuals with normal or mildly to moderately elevated levels. A study investigating the possible benefit of combining a phytosterol with fish oil found that together they significantly lowered total cholesterol, LDL-cholesterol and triglycerides, and raised HDL (“good”) cholesterol in subjects with undesirable cholesterol profiles. 257
It also seems to remain effective in individuals who are already using statin drugs to control lipid levels (both people with and without diabetes). 14,15,197 However, one study found that the standard drug gemfibrozil is more effective than fish oil for reducing triglycerides. 94 Some but not all studies suggest that fish, fish oil, or EPA or DHA separately may additionally raise the level of HDL ("good") cholesterol and possibly improve other aspects of cholesterol profile as well. 96,97,151,164,165,197 This too should help prevent heart disease.
Additionally, fish oil may help the heart by "thinning" the blood and by reducing blood levels of homocysteine , 98,176,190 although not all studies have found a positive effect. 198
Studies contradict one another on whether fish oil can lower blood pressure , 99-104,177,264 but on balance the supplement does seem to exert a modest positive effect. 174 A 6-week, double-blind, placebo-controlled study of 59 overweight men suggests that the DHA in fish oil, but not the EPA, is responsible for this benefit. 105
A large Italian trial involving almost 7,000 subjects found that fish oilmay modestly reduce the risk of death or admission to the hospital for cardiovascular reasons in patients suffering from congestive heart failure . 266 And, a smaller study involving 138 patients showed similarly beneficial results. 279
Evidence is conflicting on whether fish oil helps prevent arrhythmias . 220-224,248,285 In a 2010 study involving 663 people with intermittent atrial fibrillation (the most common cause of arrhythmia), fish oil was no more effective than placebo at reducing the number symptomatic episodes over a 24-week period. 278
Fish oil may slightly reduce heart rate . 225 This effect could contribute to preventing heart attacks and other heart problems
Old Randomized Trial, Clinical with Endpoints:
"Trials that evaluated the effects of Lovaza on clinical endpoints have also been published. Nilson et al. performed a randomized, double-blind, placebo-controlled trial to determine the effects of the study drug at a dose of 4 g daily on cardiac events and serum lipids in those patients who had had an acute myocardial infarction (AMI) within eight days of study entry.32 The results showed a significant benefit on lipids but no difference in the rate of cardiac events."