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 U.S. But what about omega-3 fatty
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
called plaque buildup on the inside of the coronary arteries. These are the blood
vessels that supply the heart muscle with oxygen and nutrients. Over time, 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 cause chest pain, called angina,
heart attack, or cardiac arrest.
Atherosclerosis starts 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. 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, maintain a healthy weight,
do moderately to intense 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 by:
Lowering the risk for abnormal heart rhythm, which can lead to sudden cardiac
Lowering triglyceride levels
Reducing the growth rate of plaque that clogs blood vessels
Lowering blood pressure slightly
Helping 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 toxins such
as mercury. 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.
Fish oil supplements
Many over-the-counter fish oil supplements are available. A prescription form is also
available. Be careful to make sure the preparation contains a significant amount of
EPA and DHA. Evidence suggests that a daily intake of 150 to 500 mg/day of EPA and
DHA may reduce cardiovascular disease risk. Ask your healthcare provider if a fish
oil supplement is right for you.