Health Information

Omega-3 Fatty Acids and Coronary Heart Disease

Most Americans eat too much fat and too many calories. Along with a lack of exercise, this has led to an epidemic of obesity and diabetes. It's also contributed to keeping heart disease as the leading cause of death in the United States. But what about omega-3 fatty acids?

Omega-3s are a helpful and important form of fat, one that your body needs but can't make. Although your body needs 2 forms of omega fatty acids, omega-3 and omega-6, it is the omega-3s that get high marks from researchers. They believe that omega-3s help prevent coronary heart disease (CHD) in healthy people and slow progress of the disease in those who already have it.

Diet and heart disease

CHD is caused by atherosclerosis. This is a long-term process in which fatty deposits of plaque build up on the inside of the coronary arteries. These are the blood vessels that supply the heart muscle with oxygen and nutrients. In the long run, the coronary arteries become so narrow that the flow of blood to the heart muscle is decreased or easily blocked by plaque or a blood clot. CHD can produce chest pain, called angina, heart attack, or both.

Atherosclerosis begins when the inside wall of an artery is damaged by inflammation or high levels of cholesterol and triglycerides. Triglycerides is another form of fat in your blood. A diet high in fat, especially saturated fat, increases cholesterol and triglycerides. Artery damage can also be caused by high blood pressure, tobacco smoke, or diabetes. You should keep your cholesterol and triglycerides at or below recommended levels. This could help prevent heart disease. According to the National Heart, Lung, and Blood Institute, that means a total cholesterol level of less than 200 mg/dL and a triglyceride level of less than 150 mg/dL.

Where omega-3s come in

To lower your levels of cholesterol and triglycerides, you should maintain a healthy weight, do moderately demanding physical activity most days of the week, eat a diet rich in vitamins, minerals, and fiber. Also include fish containing omega-3 fatty acids at least twice a week.

In the average American's diet, about 20% of calories that come from fat are omega-3 and omega-6 fatty acids. Most of the omega fatty acids are omega-6s. Experts have found that people who eat foods with high levels of 2 of the omega-3 fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), have low rates of CHD.

EPA and DHA are also called marine omega-3s because they are found in fatty fish like mackerel, lake trout, herring, sardines, albacore tuna, and salmon. They are also in supplements called fish oils. Another source for EPA and DHA is alpha-linolenic acid. This is found in soy and canola oils, flaxseed, walnuts, and other nuts. It can be changed into omega-3 fatty acids in the body, but its benefit in preventing heart disease is not as clear.

Here's how experts believe omega-3 fatty acids may reduce the risk for CHD:

  • They lower the risk for arrhythmia, an abnormal heart rhythm, which can lead to sudden cardiac death.

  • They lower triglyceride levels.

  • They lower the growth rate of plaque that clogs blood vessels.

  • They lower blood pressure slightly.

  • They help prevent inflammation of the blood vessels and formation of blood clots.

How much do you need?

The American Heart Association (AHA) recommends that healthy people who do not have heart disease eat some type of fatty fish at least twice a week. And they should include oils and foods rich in alpha-linolenic acid in their diet. Flaxseed, canola and soybean oils, and walnuts contain this acid.

Food is the best way to get omega-3 fatty acids because food contains other healthy substances. For example, fish contains arginine, glutamine, and selenium. All of these may benefit the heart and blood vessels. Flaxseed and walnuts have substances that help lower total cholesterol. 

The AHA offers this rundown on the omega-3 content of some fish, per 3-ounce serving:

  • Canned light tuna: 0.17 to 0.24 grams

  • Shrimp: 0.29 grams

  • Pollock: 0.45 grams

  • Fresh or frozen salmon: 1.1 to 1.9 grams

  • Cod: 0.15 to 0.24 grams

  • Catfish: 0.22 to 0.3 grams

  • Clams: 0.25 grams

  • Flounder or sole: 0.48 grams

  • Crabs: 0.27 to 0.4 grams

  • Scallops: 0.18 to 0.34 grams

Drawbacks of fish

Eating fish comes with a downside. There are some health risks. Some types of fish, especially the older, larger predatory fish, may contain high levels of poisons. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas.

Methylmercury is found in shark, swordfish, king mackerel, and tilefish. Tilefish is also called golden bass or golden snapper. Methylmercury is most dangerous in very young children and in women who are pregnant or likely to become pregnant. Fish low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.

Polychlorinated biphenyls (PCBs) are found in freshwater fish living in polluted waters. PCBs may cause cancer. These fish include lake trout, smelt, and freshwater bluefish. PCBs also are found in some farmed fish like salmon. Dioxin and similar compounds cause cancer, depress the immune system, and affect the central nervous system. You should check local advisory information before buying fish.

The benefits and risks of eating fish vary, depending on a person's stage of life. These are the AHA's recommendations:

  • Children, and pregnant and/or nursing women should avoid potentially contaminated fish, including shark, swordfish, king mackerel, and tilefish.

  • Middle-aged and older men, and women after menopause should follow guidelines from the FDA and Environmental Protection Agency on how much fish to safely eat. For this age group, the benefits of eating fish outweigh the risks.

  • You should eat a variety of fish to help decrease possible harmful effects from environmental pollutants.