Fish and heart disease (patient information)

For the WikiDoc page for this topic, click here


 * Assistant Editor(s)-In-Chief:

Fish Consumption Overview
Consuming fish is considered one of the best and easiest dietary choices you can make to promote your health. Fish is a good source of protein and other essential nutrients, is low in saturated fat (unlike many fatty meat products), and contains a type of heart-healthy polyunsaturated fat called omega-3 fatty acids. There are two main types of omega-3 fatty acids: EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). Research has shown that these omega-3 fatty acids are believed to reduce inflammation throughout the body, improve learning ability in children, improve symptoms associated with arthritis, while also reducing symptoms of depression, attention deficit hyperactivity disorder (ADHD), and certain skin disorders.

Furthermore, regular fish consumption is also a great dietary way to improve and promote the health of your heart. In one large, ecological study, fish ingestion was associated with a reduced risk of ischemic heart disease, all-cause mortality, and stroke mortality across 36 countries. Another study conducted with women in the Nurses' Health Study showed that a higher consumption of fish and omega-3 fatty acids among women was associated with a lower risk of coronary heart disease (CHD), especially CHD deaths. Researchers found that the risk of CHD death was 21%, 29%, 31%, and 34% lower among women who consumed fish 1-3 times per month, once per week, 2-4 times per week, and >5 times per week, respectively (p for trend=0.001), when compared to women who ate fish less than once per month.

Although not all studies have shown an association between fish consumption and reduced CHD mortality (perhaps due to differences in definitions or study methods), fish intake does appear to be related to reduced sudden cardiac death. For instance, one large prospective cohort study showed that a minimum of one fish meal per week was associated with a 52% reduction in sudden cardiac death.

Fish offers other heart-healthy benefits, including:

Triglyceride Reduction
Recent studies have indicated that omega-3 fatty acids may improve your lipid profile by lowering triglyceride levels, which may consequently lower your risk of heart disease.

The effect that omega-3 fatty acids have on triglyceride levels is dose-dependent, so the more omega-3 fatty acids consumed, the lower triglyceride levels will fall. For healthy individuals, 1 gram of omega-3 fatty acid per day can lead to a decrease in triglycerides that would help prevent sudden death from heart disease. This dose can be achieved by eating about three ounces of salmon or 3.5 ounces of trout.

However, the American Heart Association recommends that people with high triglyceride levels should consume 2-4 grams of omega-3 fatty acids per day, but only under the supervision of their doctors, as individuals consuming more than 3 grams per day are at an increased risk for bleeding.

In a review of human studies, researchers found that triglyceride levels can be reduced by 25-30% by consuming approximately 4 daily grams of omega-3 fatty acids. Additionally, omega-3 fatty acids may raise low density lipoprotein (LDL, or the “bad” cholesterol) by 5 to10%, and appear to raise high density lipoprotein (HDL, or the “good” cholesterol) by 1 to 3%.

Platelet Aggregation Reduction
Platelets play a pivotal role in the development of thrombosis (i.e. blood clots) and cardiovascular disease (CVD).

A diet including oil-rich fish is believed to reduce platelet aggregation, a marker of platelet activation that may contribute to the initiation and progression of atherosclerosis (i.e. blood clot formation).

One study compared 14 people eating 500 grams of mackerel per week (approximately equivalent to 1 g per day of EPA and DHA) for 4 weeks to 14 controls. At the end of the study, there was a 35% reduction in platelet aggregates in the dietary supplement group compared to the control group.

Membrane Stabilization / Arrhythmia Reduction
Arrhythmias occur when there is abnormal electrical activity in the heart, thereby causing the heart to beat too quickly, too slowly, or irregularly. Some arrhythmias are very minor and can be regarded as normal variants, while others are life threatening medical emergencies that can result in cardiac arrest and sudden death.

Omega-3 fatty acids are believed to have a stabilizing effect on the myocardium (heart muscle) itself so that the incidence of arrhythmias is reduced. Evidence supporting this direct effect of omega-3 fatty acids on the heart muscle comes from several different sources. First, the two main types of omega-3 fatty acids, EPA and DHA, have been shown to reduce resting heart rate and increase left ventricular filling capacity (i.e. measures of improved heart functioning).

Furthermore, an increase in heart rate variability is a physiological phenomenon in which the time interval between heart beats varies. It is associated with a reduced risk of death in patients who had previously experienced a heart attack. In 1997, researchers assessed heart rate variability in 52 patients who had previously had a heart attack. They found that increased heart rate variability was associated with the consumption of one fish meal per week.

Animal experiments have also demonstrated the anti-arrhythmic effects that fish oil can have. For instance, studies have shown that when dogs are pretreated with omea-3 fatty acids and then have an induced heart attack, those treated with the fatty acids had less damage to their heart tissue.

Additionally, stabilization of the heart muscle is a central proposed mechanism used to explain why omega-3 fatty acids seem to reduce the risk of sudden cardiac death.

Cultures with High Fish Consumption
Coronary heart disease (CHD) and CHD mortality rates remain very low in Japan, even though the Japanese have been adapting a higher-fat and higher-calorie Western diet since the end of World War II. Researchers have discovered that Japanese men have similar cholesterol and blood pressures as white Americans, with a greater smoking rate and a higher prevalence of diabetes. However, despite these risk factors, the CHD rates in Japan are still less than half of those in America.

One major difference between the American and Japanese cultures is that the Japanese typically consume fish much more regularly. Researchers set out to compare Japanese men, Japanese-American men, and white American men. They found that the Japanese men had 2-fold higher levels of omega-3 fatty acids than Japanese Americans and white Americans. Furthermore, they found that the Japanese men had the lowest levels of atherosclerosis, while the Japanese Americans and white Americans had similar levels of atherosclerosis. From these findings, the researchers concluded that very high levels of omega-3 fatty acids from a fish-based diet may contribute to a lower burden of atherosclerosis in a way that is independent of other cardiovascular risk factors and genetics.

Furthermore, the Eskimos, who also have a high fish-based diet, also have very low rates of CHD and diabetes mellitus. Dietary surveys have demonstrated that the intact of omega-3 fatty acids in Greenland Eskimos is about 14 grams per day, whereas it is only 0.2 grams per day in the United States. In addition to their low CHD and diabetes rates, total cholesterol levels tend to be low and HDL cholesterol levels tend to be high. However, it is important to note that the Eskimo diet differs from the Western diet in other ways besides the increased fish consumption, such as a low saturated fat intake.

Recommendations on the Amounts and Types of Fish to Consume
The American Heart Association (AHA) recommends that people without coronary artery disease (CAD) should consume at least two servings of a variety of fish at least twice a week, while patients with CAD should consume 1 gram of omega-3 fatty acids per day via diet or through supplementation.

Although there are many different types of fish on the market, they do not all provide the same amount of omega-3 fatty acids and are not equal in terms of the health benefits they offer. Fatty fish such as salmon, mackerel, herring, sardines, and to a lesser extent tuna and trout, contain large amounts of omega-3 fatty acids. Generally speaking, most freshwater fish have less omega-3 fatty acids than coldwater fatty fish from the sea do.

Some fish, such as catfish and tilapia, are not quite as highly recommended by health care professionals. While containing heart-healthy omega-3 fatty acids, they also contain high levels of omega-6 fatty acids, another type of polyunsaturated fat. Like omega-3s, omega-6s are considered essential fatty acids that are necessary for human health. They play a vital role in brain function, support normal growth and development, lower cholesterol, support skin health, and help our blood clot. However, when consumed in excess, they can lead to blood clots, and cause inflammation and oxidation, thereby potentially increasing the risk for arthritis, inflammatory bowel disease (IBS) and certain cancers.

Instead of completely avoiding fish like tilapia and catfish, the key lies in maintaining a healthy balance of omega-3 and omega-6 fatty acids in our diet. Experts suggest this ratio should be 4 parts omega-3s to 1 part omega-6s, but the typical American diet does not adhere to this guideline. In fact, the usual American diet has a ratio of 20 parts omega-6s to 1 part omega-1, says nutritionist Lona Sandon, RD, a spokeswoman for the American Dietetic Association. For this reason, consuming fish with higher levels of omega-3 fatty acids is considered to be better for our health.

Finally, eating too much of certain types of fish can carry other health risks, as some fish carry high levels of mercury, PCBs (polychlorinated biphenyls), and other environmental contaminants. Larger, older, predatory fish and marine mammals, such as shark, swordfish, king mackerel or tilefish, tend to have the highest amounts of these substances. The U.S. Food and Drug Administration (FDA) advises children and pregnant women to avoid eating fish with the highest mercury levels, but that this group should still eat up to 12 ounces per week of fish that are lower in mercury, such as salmon, pollock, catfish, and canned light tuna.

Fish vs. Fish Oil Capsules
Although some people may choose to simply take a fish-oil capsule, many nutritionists recommend eating the fish itself when possible. Fish offers more of a balanced source of nutrients than what can be provided in just the fish oil supplements. There could be other components in the fish other the omega-3 fatty acids that make it so healthy, such as amino acids, that are lacking in the supplements. Furthermore, “there is something about whole food that when it goes into the body, it’s more than 90% absorbed, while [with] a supplement you absorb only about 50%,” says nutritionist Lona Sandon, RD, a spokeswoman for the American Dietetic Association.

Moreover, supplements are not regulated in the United States. Therefore, certain fish oil[ capsules may actually contain concentrated amounts of the same toxins found in the fish itself, so contrary to what some may believe, fish oil supplements may not help you avoid the contamination risks of fresh fish. Finally, since a capsule is easier to swallow than a fish fillet is to eat, it is possible to overdose on fish oil supplements, which can increase the risk of bruising or bleeding.