Fish oils are derived from such cold-water fish as salmon, cod, tuna, or mackerel. They have recently acquired a new visibility as dietary supplements because they are high in omega-3 fatty acids. Omega-3 fatty acids, together with the omega-6 fatty acids, are important components of a healthful diet.
The body cannot manufacture them, therefore they must be obtained from grains, fruits, vegetable oils, and other foods. In addition, people should consume a balanced ratio of omega-6 and omega-3 fatty acids. Some researchers believe that these two types of fatty acids should be consumed in a 1:1 ratio, while others maintain that people should obtain several times more omega-3 than omega-6 fatty acids from their diet.
In either case, the fact that fish oils are high in omega-3 fatty acids may help people to maintain a good balance between the two types of fatty acids. The most important types of omega-3 fatty acids found in fish oils are eicosapentanoic acid (EPA) and docosahexaenoic acid (DHA). The body needs EPA to produce prostaglandins, which are hormone-like substances that help to protect the heart and the cell membranes. DHA is required for the normal development of the brain, the eyes, and the reproductive system.
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General use
In general, fish oils are recommended as dietary supplements to lower the levels of triglycerides in the blood, counteract inflammation in various parts of the body, and thin the blood.
Heart disease and stroke
The omega-3 fatty acids in fish oils increase the concentrations of good cholesterol (high density lipoproteins, HDL) in the blood while decreasing the concentrations of bad cholesterol (triglycerides). They also lower the total cholesterol level.
Furthermore, these omega-3 oils protect the heart by preventing the formation of blood clots and fatty deposits (plaque) on the arterial walls. In people with coronary heart disease, fish oils may help to reduce the risk of blood clots in the brain or in the lungs; pain associated with angina; and the risk of cardiac arrythmias.
The benefits of omega-3 fatty acids have been shown in clinical studies. Investigation of the possible benefits of fish oils began when researchers discovered that Eskimos rarely suffer from heart attacks or rheumatoid arthritis (RA) even though their diet is high in fat from fish, seals, and whales. Because these sources of fat have a high omega-3 fatty acid content, it was assumed that the type of fatty acid that they contained helped to protect the Eskimos from the usual consequences of high-fat diets.
Later studies confirmed that diets high in omega-3 fatty acids decrease the risk of heart attacks, strokes, and abnormal heart rhythms. In one study of 20,551 doctors, those who ate at least one fish meal per week cut their risk of heart attacks in half compared to those who ate fish once a month or less. In the five-year Lyon study, men who followed a Mediterranean diet with emphasis on omega-3-rich oils, fish, fruits, and vegetables had their heart attack rates reduced by 70% compared to subjects in the control group.
One question, however, is whether fish oil used by itself as a dietary supplement is as effective as a diet high in fish, since the two are not the same. One open trial of 11,324 people who were followed for three to five years found that fish oil did reduce the risk of death from heart attack. This study, however, was not a double-blind study, and its results cannot be taken as conclusive.
High blood pressure
Fish oils may help to control high blood pressure. Several studies have shown that taking fish oil can lower blood pressure. On the other hand, a 1997 study involving 2,000 subjects found no significant effect.
Rheumatoid arthritis
Fish oil may be useful in managing the symptoms of early rheumatoid arthritis (RA). A significant reduction in joint tenderness, morning stiffness, and fatigue, coupled with an increase in grip strength, has been observed in patients taking fish oil capsules. Fish oil appears to reduce the symptoms of RA without side effects, and to increase the effectiveness of standard medications for it. Fish oil does not, however, appear to slow the progress of RA.
Asthma
It has been claimed that fish oils reduce inflammation of the airways and may prevent asthma attacks. According to one author, allergic disorders such as asthma may be triggered by too much omega-6 and too little omega-3 fats in the diet. Two studies undertaken in 1994 and 1996 respectively, however, found no benefits from using fish oil in the management of asthma.
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Psoriasis and autoimmune disorders
Several small studies indicate that fish oil may be helpful in treating psoriasis, which is an inflammatory disorder of the skin; in lupus; and in Raynaud’s phenomenon, an autoimmune disorder in which the patient’s hands and feet are abnormally sensitive to cold and emotional stress. With respect to the Raynaud’s patients, small double-blind studies showed that very high doses of fish oil reduce their responses to cold.
It appears, however, that doses as high as 12 g of fish oil daily are necessary to provide this effect. With respect to lupus, a small study of 30 subjects found that 14 out of 17 patients given daily doses of 20 g of EPA derived from fish oil had significant improvement. Subjects given a placebo either showed no improvement or got worse.
Osteoporosis
When taken together with calcium, essential fatty acids may help to protect women from osteoporosis. One 18-month study of 65 postmenopausal women found that those who were given a combination of omega-6 fatty acids (GLA) and omega-3 fatty acids from fish oil together with calcium had higher bone density and fewer fractures than those who were given the calcium and a placebo.
Gynecological problems
Fish oil supplements may be helpful in alleviating the symptoms of premenstrual syndrome (PMS) and painful periods. A number of different substances that are high in fatty acids, including flaxseed oil and GLA as well as fish oil, have been recommended for painful menstrual periods. One four-month study of adolescents suggests that fish oil is useful in treating this condition.
Forty-two young women were divided into two groups; half received a daily dose of 6 g of fish oil for two months, followed by two months of placebo. The other half received the placebo and fish oil in reverse order. The results indicated that the subjects had significantly less menstrual pain while taking the fish oil.
Bipolar disorder and depression
Fish oil does appear to offer considerable benefits to people with bipolar disorder. A four-month double-blind study of 30 subjects indicated that fish oil improves emotional stability and helps to prevent relapses. Of the 14 persons who took fish oil, 11 stayed well or improved, while only six out of 16 subjects given placebos stayed well.
A 2001 report looked at the effects of fish oil on mood and depression. Two large studies showed a strong connection between rates of depression and bipolar disorder in countries with high amounts of fish in diets. Although researchers cannot say that fish oil is the only reason for the difference, evidence continues to mount that omega-3 and omega-6 fatty acids may work as mood stabilizers.
Other conditions
Fish oil has been touted as a useful treatment for diabetic neuropathy, allergies, migraine headaches, Crohn’s disease, gout, and ulcerative colitis, but there has been little systematic research involving these applications. In addition, health food manufacturers list hair loss, memory problems, muscle strain, failing eyesight, liver complaints, rickets, and dental problems as ailments that can be treated with fish oil. No clinical studies have been cited in support of these claims.
Early studies in laboratories indicate that fish oils might prolong life in people with automimmune disorders like diabetes. Early results show that a diet high in fish oils helped improve immune system function in these patients.
Preparations
There is no minimum daily requirement of fish oil as such, but a healthy diet should supply at least 5 g of essential fatty acids every day. Typical doses of fish oil are 3–9 g daily, although some participants in research studies have taken much higher doses. If fish oil is taken as a dietary supplement, it should be taken in large enough doses to supply about 1.8 g of EPA and 0.9 g of DHA on a daily basis.
Fish oil capsules are available in health food stores as over-the-counter items; prices range from $7 for 180 capsules of Norwegian cod liver oil to $14 for 180 capsules of salmon oil. Capsules of tuna oil and halibut liver oil are also available from several commercial suppliers.
Precautions
Fish oil can easily become rancid. The capsules can be stored in the refrigerator to slow the rate of oxidation. Another option is to purchase capsules that have added vitamin E.
The type of fish oil may make a difference. Although cod liver oil is the easiest form to obtain, it can cause a buildup of vitamin A and vitamin D in the body because these two vitamins are fat-soluble. Pregnant women should not take more than 2,500 IU of vitamin A per day because higher amounts can cause birth defects.
Other adults should not consume more than 5,000 IU of vitamin A per day. Vitamin D can produce toxicity when taken at levels above 1,000 IU daily for long periods of time. Persons who obtain their fish oil from cod liver oil should check the label to see how much vitamin A and vitamin D it contains. It may be prudent to take salmon oil, mackerel oil, or oil from other coldwater fish.
Women who are pregnant or breast-feeding should talk to their physicians before taking fish oil supplements or any other medications.
Because fish oil can thin the blood, it should not be taken together with aspirin and other nonsteroidal antiinflammatory drugs (NSAIDs, or over-the-counter pain killers), Coumadin (warfarin), or other anti-clotting medications. Fish oil does not seem to cause problems with bleeding when it is taken by itself, however.
Side effects
Fish oil generally appears to be safe when taken as a dietary supplement. The most common side effects are mild indigestion or a fishy taste in the mouth.
Interactions
Fish oil supplements may interact with nonsteroidal anti-inflammatory drugs (NSAIDs), warfarin, or other anti-clotting medications to cause excessive bleeding.
