Fueled by media reports of health benefits coupled with convincing marketing materials, fish oil supplements have now become the 3rd most widely used dietary supplement in the US.
Fish oil supplements provide omega-3 fatty acids, whose reported benefits include reducing triglyceride levels, decreasing blood pressure, reducing the risk of cardiovascular disease, improving symptoms of depression, ADHD, and Alzheimer’s and minimizing vision issues like glaucoma and age-related macular degeneration. But how strong is the science? Is it clear enough to support its widespread use?
Fish oil first became linked to cardiovascular disease in the 1970s when Danish scientists studying the food habits of Inuits in northern Greenland observed that this population consumed diets rich in omega-3 fatty acid foods. Noting that they also had low rates of cardiovascular disease, the scientists hypothesized that the two might be related.
What is the evidence for cardiovascular benefits from fish oil?
There have been several large studies looking at the role of fish oil in reducing future coronary events for patients who already had or were at high risk for heart disease. The GISSI Pervenizione study in the late 1990s randomized 11,000 people who had had a recent heart attack to take either 1 gm of omega-3 fatty acids, 300 mg of Vitamin E, both or nothing to see if there was a decrease in future cardiovascular events. The JELIS study, also in the late 1990s, followed 18,000 Japanese who had high cholesterol to test the effect of omega-3 supplements on future major coronary events. In both studies people who took the omega-3 supplements had a lower risk for coronary events than those who did not.
These early studies suggested that omega-3 supplements might be effective in preventing heart disease, hence the rush to buy these products. But more recent studies have not been able to replicate the same positive results. Three studies, all published within the last 3 years and following almost 30,000 patients who took omega-3 supplements, did not show any reduction in the risk for major cardiovascular events compared to patients who were not taking supplements. The only positive result consistently found was a reduction in triglyceride levels in the supplement group.
Why the discrepancy?
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One hypothesis for the difference between the earlier and later studies is that many of the beneficial results were found in studies conducted in the mid to late 1990s or earlier, when the use of statins and other newer medications to treat cardiovascular disease were less widely used than today. Researchers believe that omega-3 fatty acids may provide some reduction in the risk for cardiovascular disease for patients not on statins, but this small benefit may be obscured by the greater benefit and risk reduction seen with the use of statins and other cardio protective treatments in standard use today.
What’s next?
There are more studies underway that may shed new light on the role that omega 3 fatty acids play in cardiovascular disease, both for patients already at high risk and for patients who do not currently have heart disease. But in the meantime, those hoping to keep their hearts healthy would benefit from focusing on eating more seafood, including fatty fish like salmon, mackerel, sardines, and bluefish which are all good sources of omega-3 fatty acids.