Dear Doctor: I have been taking fish oil capsules daily over the last five years. Is there any benefit in doing this?
Dear Reader: The short answer is "maybe." Scientists have shown that societies with higher fish intake have lower rates of heart disease. The belief is that this benefit comes from fish oil. Fish oil contains substances known as long-chain fatty acids (omega-3 fatty acids), specifically DHA, DPA and EPA, with many health benefits. These fatty acids help lower blood triglyceride levels; lower blood pressure (by 1.5 to 4 points); and have an ability to help the heart relax so that blood flows more easily into its chambers. Furthermore, the omega-3 fatty acids in fish oil have also been linked to a slightly slower heart rate and to a decrease in inflammation.
Small studies have shown that fish oil may be linked to a slight reduction in the formation of plaque in the arteries that supply the heart, but evidence of its ability to reduce the rates of heart attack hasn't been as robust or as statistically significant.
One fish oil finding that was indeed statistically significant was from a large study published in the Journal of the American Medical Association in 2006. That study linked fish oil intake of 250 milligrams per day to a 36 percent reduction in rates of sudden cardiac death. That amount -- 250 mg of fish oil -- equals 1 to 2 servings of fish per week.
One other property that fish oil may have is an ability to reduce electrical excitability of the heart. That reduced excitability may decrease the heart's chances of going into an abnormal rhythm, which can lead to death. Furthermore, among people who have had a heart attack, 1 gram of fish oil per day has been linked to a significant decrease in death rates. The benefits of fish oil have been seen as early as four months after a heart attack and even as late as 36 months after a heart attack. Again, this appears to be related to fish oil's potential protective effect against abnormal heart rhythms after a heart attack.
Fish oil hasn't been shown to decrease the chance of a stroke. Nor has it been shown to decrease the risk or incidence of cancer. In fact, some studies have shown a correlation between fish oil and prostate cancer, but other studies have failed to support that connection.
In summary, fish oil does appear to decrease the chance of sudden cardiac death, but you don't need to take capsules to see this benefit. Eating fish twice a week can do that.
Before you turn to eating tuna fish from a can, keep in mind that tuna has much less omega-3 fatty acids than Atlantic salmon, mackerel or herring. If you don't care for fish, taking 1 gram of a fish oil supplement twice a week will likely yield a benefit. If you've had a heart attack, consider taking 1 gram of fish oil a day.
(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)
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