Diet & Fitness

 

Many double-blind trials have demonstrated that fish oils (also called fish-oil concentrates) containing EPA and DHA (mentioned above) lower TG levels.¹ The amount of fish oil used in much of the research was an amount that provided 3,000 mg per day of omega-3 fatty acids. To calculate how much omega-3 fatty acid is contained in a fish oil supplement, add together the amounts of EPA and DHA. For example, a typical 1,000-mg capsule of fish oil provides 180 mg of EPA and 120 mg of DHA (total omega-3 fatty acids equals 300 mg). Ten of these capsules would contain 3,000 mg of omega-3 fatty acids. Other sources of omega-3 fatty acids, such as flaxseed oil, do not lower TGs. While flaxseed oil has other benefits, it should not be used for the purpose of reducing TGs.

Cod liver oil, another source of omega-3 fatty acids, has also been found to lower TGs.² Cod liver oil is less expensive than the fish oil concentrates discussed previously. However, cod liver oil also contains relatively large amounts of vitamin A and vitamin D; too much of either can cause side effects. In contrast, fish oil concentrates have little or none of these vitamins. Individuals wishing to use cod liver oil as a substitute for a fish-oil concentrate should consult a doctor.

Omega-3 fatty acids from fish oil and cod liver oil have been reported to affect blood in many other ways that might lower the risk of heart disease.³ However, these supplements sometimes increase LDL cholesterol—the bad form of cholesterol. A doctor can check to see if fish oil has this effect on an individual. Research shows that when 900 mg of garlic extract is added to fish oil, the combination still dramatically lowers TG levels but no longer increases LDL cholesterol.⁴ Therefore, it appears that taking garlic supplements may be a way to avoid the increase in LDL cholesterol sometimes associated with taking fish oil. People who take fish oil may also need to take vitamin E to prevent the oil from undergoing potentially damaging oxidation in the body.⁵ It is not known how much vitamin E is needed to prevent such oxidation. The amount required would presumably depend on the amount of fish oil used. In one clinical trial, 300 IU of vitamin E per day prevented oxidation damage in individuals taking 6 grams of fish oil per day.⁶

EPA and DHA, the long-chain polyunsaturated omega-3 fatty acids found in fish oil, have been shown to improve blood vessel function and lower blood pressure.⁷ Although a large observational study that followed 12,279 men for an average of 15.8 years found no relationship between omega-3 fatty acid intake and risk of high blood pressure,⁸ multiple studies have noted higher blood levels of these fatty acids, and especially DHA, are associated with reduced incidence of hypertension.⁹ Furthermore, a meta-analysis of 70 randomized controlled trials found supplementing with at least 2 grams of EPA plus DHA per day significantly reduces systolic and diastolic blood pressure, and the effect is stronger in those with hypertension.¹⁰

In a double-blind study of patients with chronic heart failure, supplementation with the fatty acids present in fish oil for an average of four years resulted in a small but statistically significant decrease in the number of patients who died or were hospitalized for cardiovascular reasons. The treatment consisted of 850 to 882 mg per day of a mixture of eicosapentaenoic acid and docosahexaenoic acid (as their ethyl esters).¹¹ In another double-blind trial, supplementation with eicosapentaenoic acid and docosahexaenoic acid improved heart function and decreased the number of hospitalizations in patients with heart failure due to dilated cardiomyopathy.¹²

 

Supplementation with fish oil, rich in omega-3 fatty acids, has been associated with favorable changes in various risk factors for atherosclerosis and heart disease in some,^{13,14,15,16,17,18} but not all, studies.^19,20,21 A double-blind trial showed that people with atherosclerosis who took fish oil (6 grams per day for 3 months and then 3 grams a day for 21 months) had significant slowing of progression of atherosclerotic plaques and a decrease in cardiovascular events (for example, heart attack and stroke) compared with those who did not take fish oil.²² These results contradict the findings of an earlier controlled trial in which fish oil supplementation for two years (6 grams per day) did not promote major favorable changes in the diameter of atherosclerotic coronary arteries.²¹

 

Fish oil, which contains the fatty acids known as EPA and DHA, has been studied in the treatment of angina. In some studies, enough fish oil to provide a total of about 3 grams of EPA and 2 grams of DHA has reduced chest pain as well as the need for nitroglycerin;²³ other investigators could not confirm these findings.²⁴ People who take fish oil may also need to take vitamin E to protect the oil from undergoing potentially damaging oxidation in the body.²⁵ It is not known how much vitamin E is needed to prevent such oxidation; the amount required would presumably depend on the amount of fish oil used. In one study, 300 IU of vitamin E per day prevented oxidation damage in individuals taking 6 grams of fish oil per day.²⁶

Fish oil contains the beneficial omega-3 fatty acids EPA and DHA, which have led to partial reversal of atherosclerosis in a double-blind trial.²⁷ In another double-blind trial, individuals were given either fish oil (containing about 1 gram of EPA and 2/3 gram of DHA) or mustard oil (containing about 3 grams alpha linolenic acid, another omega-3 fatty acid) 18 hours after a heart attack. Both groups experienced fewer nonfatal heart attacks compared to a placebo group, while the fish oil group also experienced fewer fatal heart attacks.²⁸ The largest published study on omega-3 fatty acids for heart attack prevention was the preliminary GISSI Prevenzione Trial,²⁹ which reported that 850 mg of omega-3 fatty acids from fish oil per day for 3.5 years resulted in a 20% reduction in total mortality and a 45% decrease in sudden death. Other investigators suggest that fish oil reduces the amount of heart muscle damage from a heart attack and enhances the effect of blood-thinning medication.³⁰ People wishing to supplement with fish oil should take fish oil supplements that include at least small amounts of vitamin E, which may protect this fragile oil against free radical damage.³¹

 

Men with intermittent claudication consumed a fortified milk product or regular milk daily for one year. The fortified product provided daily 130 mg of eicosapentaenoic acid and 200 mg of docosahexaenoic acid (EPA and DHA, two fatty acids in fish oil), small amounts of supplemental vitamin E, folic acid, and vitamin B6, and additional amounts of oleic acid and alpha-linolenic acid. Compared with regular milk, the fortified milk product significantly increased the distance the participants could walk before the onset of pain.³²

In a double-blind trial, supplementation with 12 large capsules of fish oil per day (providing 4 grams of eicosapentaenoic acid [EPA] per day) for 6 or 12 weeks reduced the severity of blood-vessel spasm in 5 of 11 people with Raynaud’s phenomenon.³³ Fish oil was effective in people with primary Raynaud’s disease, but not in those whose symptoms were secondary to another disorder.

 

In a double-blind trial, people with a type of arrhythmia known as ventricular premature complexes were supplemented for 16 weeks with either 15 ml (1 tbsp) per day of fish oil or a similar amount of safflower oil as placebo. Patients taking the fish oil had a significantly reduced frequency of abnormal heartbeats compared with those receiving placebo, and 44% of those receiving fish oil experienced at least a 70% reduction in the frequency of abnormal beats.³⁴ In a separate study, however, men given 20 ml (4 tsp) of cod liver oil per day for six weeks, beginning one week after a heart attack, had the same frequency of irregular heart beats as did men given no supplemental oil.³⁵ In a double-blind study, people who had a history of certain potentially life-threatening arrhythmias—sustained ventricular tachycardia or ventricular fibrillation—had an increase in the recurrence rate of these arrhythmias when they took fish oil.³⁶ A similar study found no adverse effect of fish oil supplements in people with these serious arrhythmias.³⁷ Because of these conflicting findings, people with a history of either of these arrhythmias should consult a doctor before taking fish oil.

 

A greater intake of the omega-3 fatty acids found in fish oils has been linked to reduced risk of COPD,³⁸ though research has yet to investigate whether fish oil supplements would help people with COPD. In a double-blind trial, people with COPD received a fatty acid supplement (providing daily 760 mg of gamma-linolenic acid, 1,200 mg of alpha-linolenic acid, 700 mg of eicosapentaenoic acid, and 340 mg of docosahexaenoic acid) or a placebo (80% palm oil and 20% sunflower oil) during an eight-week rehabilitation program. Compared with the placebo, the fatty acid supplement significantly improved exercise capacity.³⁹ While two of the fatty acids supplied in this supplement (eicosapentaenoic acid [EPA] and docosahexaenoic [DHA] acid) are found in fish oil, is not known which components of the supplement were most responsible for the improvement. Gamma-linolenic acid is found in evening primrose oil, black currant seed oil, and borage oil; alpha-linolenic acid is found in flaxseed oil and other oils.

 

Omega-3 fatty acids found in fish oil, particularly DHA, are needed for normal nervous system function. Depressed people have been reported to have lower omega-3 fatty acid levels (for example, DHA) than people who are not depressed.^40,41,42,43 Low levels of the other omega-3 fatty acid from fish, EPA, have correlated with increased severity of depression.⁴⁴ In some double-blind trials, supplementation with various amounts of fish oil was beneficial for the treatment of depression in both children and adults,^45,46 but fish oil was ineffective in other double blind trials.^47,48

EPA alone has also been reported to be beneficial. There is one case report of a man with a long history of severe depression who showed clear improvement within one month of starting a purified EPA supplement (4 grams per day of the ethyl ester of eicosapentaenoic acid [E-EPA]).⁴⁹ In a double-blind study, supplementation with E-EPA for 12 weeks was significantly more effective than a placebo at relieving symptoms of depression.⁵⁰ E-EPA was beneficial, even though the participants in the study had failed to respond adequately to conventional antidepressant drugs. The conventional medications were continued during treatment with E-EPA or placebo. An effective level of intake was 1 gram per day, whereas larger amounts of E-EPA resulted in little or no benefit. The authors of the study suggested that taking too much E-EPA might cause an imbalance with other essential fatty acids, which could reduce the effectiveness of the treatment.

In a double-blind trial, fish oil was significantly more effective than a placebo in improving anxiety levels in a group of substance abusers (alcohol, cocaine, and/or heroin).⁵¹ The fish oil used in this study provided 3 grams per day of omega-3 fatty acids and was given for three months.

Diets low in omega-3 fatty acids (EPA and DHA) have been associated with menstrual pain.⁵² In one double-blind trial, supplementation with fish oil, a good source of omega-3 fatty acids, led to a statistically significant 37% drop in menstrual symptoms. In that report, adolescent girls with dysmenorrhea took an unspecified amount of fish oil that provided 1,080 mg of EPA and 720 mg of DHA per day for two months to achieve this result.⁵³ A double-blind trial found that the same amount of EPA and DHA plus 7.5 mcg per day of vitamin B12 led to a greater than 50% decrease in menstrual symptoms, but a group taking only fish oil did not obtain as much relief.⁵⁴ Six grams of fish oil per day provides the approximate levels of EPA and DHA used in these trials. In another double-blind trial, 1 gram per day of fish oil significantly decreased pain intensity, compared with a placebo, in women with dysmennorhea.⁵⁵

 

Supplementation with fish oil (providing either 2.7 g or 6.1 g per day of the omega-3 fatty acids EPA and DHA) significantly reduced recurrence of premature delivery, according to data culled from six clinical trials involving women with a high risk for such complications.⁵⁶ Fish oil supplementation did not prevent premature delivery of twin pregnancies, nor did it have any preventive effect against intrauterine growth retardation or pregnancy-induced hypertension. Fish oils should be free of contaminants, such as mercury and organochlorine pesticides. Women who eat substantial amounts of certain types of seafood (e.g., swordfish, tuna) may be consuming contaminants that can increase the risk of brain and nervous system abnormalities in their offspring. Exposure to mercury and polychlorinated biphenyls (PCBs) was found to be increased in relation to maternal intake of seafood. Higher exposure to these toxic contaminants has been linked to an increased risk of deficits in the developing brains and nervous systems of the children.⁵⁷

The DHA found in fish oil is essential for the development of the visual system in infants.⁵⁸ In one double-blind study, 103 term infants were randomly assigned to receive either formula with no docosahexaenoic acid (DHA) or arachidonic acid (ARA) or formula supplemented with DHA and ARA at concentrations similar to those found in human milk, starting when they were six days old. Visual maturation was assessed by measuring sweep visual evoked potential at ages 6, 17, 26, and 52 weeks. At each age, the supplemented group measured better, which led researchers to conclude that long-term supplementation of infant formula with DHA and ARA in amounts typical in human milk may help enhance visual development during the first year of life.

 

Animal research suggests that fish oils may reduce the severity of endometriosis,^59,60 and fish oils have been shown to improve symptoms of dysmenorrhea (painful menstruation),⁶¹ which may be caused by endometriosis. Therefore, while no specific research has been done on the effects of fish oils in women with endometriosis, some health practitioners recommend several grams of fish oil per day for this condition.

 

In a double-blind study, supplementation with a proprietary blend of acetyl-L-carnitine, omega-3 fatty acids from fish oil, and coenzyme Q10 for 12 months resulted in an improvement in both visual function and in objective findings on eye examination (a decrease in the drusen-covered area on the retina).⁶²

An assessment of 3,654 Australians aged 49 years or older found an association between a diet high in omega-3 fatty acids from fish and a lower risk of age-related macular degeneration.⁶³

 

In a double-blind trial, supplementing with the fatty acids present in fish oil (0.6 grams per day of EPA and 1.7 grams per day of DHA) for six months was not beneficial in people with Alzheimer's disease. However, in the subgroup of people with very mild cognitive impairment, supplementation with these fatty acids slowed the rate of cognitive decline compared with a placebo.⁶⁴

Many double-blind trials have proven that omega-3 fatty acids in fish oil, called EPA and DHA, partially relieve symptoms of RA.^{65,66,67,68,69,70,71,72,73} The effect results from the anti-inflammatory activity of fish oil.⁷⁴ Many doctors recommend 3 grams per day of EPA and DHA, an amount commonly found in 10 grams of fish oil. Positive results can take three months to become evident. In contrast, a double-blind trial found flaxseed oil (source of another form of omega-3 fatty acid) not to be effective for RA patients.⁷⁵

The omega-3 fatty acids present in fish oil, EPA and DHA, have anti-inflammatory effects and have been studied primarily for rheumatoid arthritis, which involves significant inflammation. However, osteoarthritis also includes some inflammation.⁷⁶ In a 24-week controlled but preliminary trial studying people with osteoarthritis, people taking EPA had “strikingly lower” pain scores than people who took placebo.⁷⁷ However, in a double-blind trial by the same research group, supplementation with 10 ml of cod liver oil per day was no more effective than a placebo.⁷⁸

 

In a double-blind trial, fish oil (10 grams per day) was found to improve the skin lesions of psoriasis.⁷⁹ In another trial, supplementing with 3.6 grams per day of purified eicosapentaenoic acid (EPA, one of the fatty acids found in fish oil) reduced the severity of psoriasis after two to three months.^80,81 That amount of EPA is usually contained in 20 grams of fish oil, a level that generally requires 20 pills to achieve. However, when purified EPA was used in combination with purified docosahexaenoic acid (DHA, another fatty acid contained in fish oil), no improvement was observed.⁸²

Additional research is needed to determine whether fish oil itself or some of its components are more effective for people with psoriasis. One trial showed that applying a preparation containing 10% fish oil directly to psoriatic lesions twice daily resulted in improvement after seven weeks.⁸³ In addition, promising results were reported from a double-blind trial in which people with chronic plaque-type psoriasis received 4.2 g of EPA and 4.2 g of DHA or placebo intravenously each day for two weeks. Thirty-seven percent of those receiving the essential fatty acid infusions experienced greater than 50% reduction in the severity of their symptoms.⁸⁴

Supplementing with fish oil also may help prevent the increase in blood levels of triglycerides that occurs as a side effect of certain drugs used to treat psoriasis (e.g., etretinate and acitretin).⁸⁵

 

Ten grams of fish oil providing 1.8 grams of EPA (eicosapentaenoic acid) per day were given to a group of eczema sufferers in a double-blind trial. After 12 weeks, those using the fish oil experienced significant improvement.^86,87 According to the researchers, fish oil may be effective because it reduces levels of leukotriene B4, a substance that has been linked to eczema.⁸⁸ The eczema-relieving effects of fish oil may require taking ten pills per day for at least 12 weeks. Smaller amounts of fish oil have been shown to lack efficacy.⁸⁹

One trial using vegetable oil as the placebo reported that fish oil was barely more effective than the placebo (30% vs. 24% improvement).⁹⁰ As vegetable oil had previously been reported to have potential therapeutic activity, the apparent negative outcome of this trial should not dissuade people with eczema from considering fish oil.

 

In a small preliminary trial, supplementation with fish oil (10 grams per day for three months) reduced photosensitivity in 90% of people suffering from polymorphous light eruptions.⁹¹

 

One older controlled trial found that children given 3 teaspoons of cod liver oil per day (containing roughly 800 IU of vitamin D) for an entire school year had over 50% fewer new cavities.⁹² These promising results have not been followed up with modern placebo-controlled trials.

In a double-blind trial, fish oil was significantly more effective than a placebo in improving anxiety levels in a group of substance abusers (alcohol, cocaine, and/or heroin).⁹³ The fish oil used in this study provided 3 grams per day of omega-3 fatty acids and was given for three months.

 

There are two different classes of essential fatty acids: omega-6 fatty acids and omega-3 fatty acids. There is considerable evidence these fatty acids are deficient, or are not used properly, in people with schizophrenia.^{94,95,96,97,98,99} Some investigators suggest this altered fatty acid metabolism may be involved in the increased need for niacin seen in some schizophrenic patients.¹⁰⁰ A case has been reported in which a man with schizophrenia had dramatic and sustained improvement while being supplemented with 2 grams daily of omega-3 fatty acids.¹⁰¹ In a preliminary trial, schizophrenic patients receiving omega-3 fatty acids showed improvement in symptoms, as well as a reduction in adverse effects from their anti-psychotic medications.¹⁰² Another study found that people with schizophrenia had lower blood levels of both omega-3 and omega-6 fatty acids, compared with non-schizophrenic people, even though both groups were consuming similar amounts of these fatty acids.¹⁰³ In a separate preliminary study, higher intake of omega-3 fatty acids was associated with less severe disease, and supplementation with 10 grams of concentrated fish oil, a source of omega-3 fatty acids, led to significant improvement in symptoms over a six-week period.¹⁰³ In a double-blind trial, supplementation with fish oil (providing 2.2 g per day of the combination of eicosapentaenoic acid and docosahexaenoic acid) for 26 weeks decreased symptom severity, compared with a placebo, in a group of patients hospitalized with a first episode of schizophrenia.¹⁰⁵ In addition, a double-blind trial found that supplementing with 1.2 g per day of omega-3 fatty acids from fish oil prevented the development of psychosis in adolescents and young adults who were at very high risk of developing a psychotic disorder.¹⁰⁶

In a double-blind trial that included 87 patients with chronic schizophrenia or a related illness (schizoaffective disorder), supplementation with 3 grams per day of eicosapentaenoic acid (one of the omega-3 fatty acids found in fish oil) was ineffective.¹⁰⁷ The patients in this negative study were older and had been ill for longer, compared with patients in earlier studies who improved with omega-3 fatty acid supplementation.

Several clinical trials have examined the effects of supplementation with essential fatty acids in people with schizophrenia, with inconsistent results.^{108,109,110,111} While the results of trials using omega-3 fatty acids are promising, further double-blind trials are needed to establish whether fatty acid supplementation is an effective therapy for schizophrenia. Trials of omega-6 fatty acids (like GLA from borage oil) have yielded predominantly negative results.¹¹²

People diagnosed with depression may have lower blood levels of omega-3 fatty acids.^112,113 A double-blind trial found that bipolar patients taking 9.6 grams of omega-3 fatty acids from fish oil per day in addition to their medications had significant improvements compared with those taking placebo.¹¹⁴ Similar benefits were reported in a preliminary trial that used 1.5 to 2 grams per day of pure eicosapentaenoic acid, a component of fish oil.^[REF] However, in another double-blind trial, 8 grams per day of fish oil taken for 4 months was of no benefit for patients with bipolar disorder.^[REF] In a preliminary trial, children with bipolar disorder saw benefits from omega-3 fatty acids (1,290 to 4,300 mg per day) from fish oil given for eight weeks.¹¹⁵

A preliminary trial found that elderly women with osteoporosis who were given 4 grams of fish oil per day for four months had improved calcium absorption and evidence of new bone formation.¹¹⁶ Fish oil combined with evening primrose oil (EPO) may confer added benefits. In a controlled trial, women received 6 grams of a combination of EPO and fish oil, or a matching placebo, plus 600 mg of calcium per day for three years.¹¹⁷ The EPO/fish oil group experienced no spinal bone loss in the first 18 months and a significant 3.1% increase in spinal bone mineral density during the last 18 months.

A preliminary trial found that elderly women with osteoporosis who were given 4 grams of fish oil per day for four months had improved calcium absorption and evidence of new bone formation.¹¹⁸ Fish oil combined with evening primrose oil (EPO) may confer added benefits. In a controlled trial, women received 6 grams of a combination of EPO and fish oil, or a matching placebo, plus 600 mg of calcium per day for three years.¹¹⁹ The EPO/fish oil group experienced no spinal bone loss in the first 18 months and a significant 3.1% increase in spinal bone mineral density during the last 18 months.

 

In a double-blind study, supplementation with a proprietary blend of acetyl-L-carnitine, omega-3 fatty acids from fish oil, and coenzyme Q10 for 12 months resulted in an improvement in both visual function and in objective findings on eye examination (a decrease in the drusen-covered area on the retina).¹²⁰

 

Surveys have shown that Inuit people, who consume large amounts of omega-3 fatty acids, have a much lower incidence of some types of glaucoma than do Caucasians. Although there have been no studies on the use of omega-3 fatty acids to treat glaucoma, one study found that cod liver oil (a rich source of omega-3 fatty acids) reduced intraocular pressure in animals.¹²¹

An assessment of 3,654 Australians aged 49 years or older found an association between a diet high in omega-3 fatty acids from fish and a lower risk of age-related macular degeneration.¹²²

Diets low in omega-3 fatty acids (EPA and DHA) have been associated with menstrual pain.¹²³ In one double-blind trial, supplementation with fish oil, a good source of omega-3 fatty acids, led to a statistically significant 37% drop in menstrual symptoms. In that report, adolescent girls with dysmenorrhea took an unspecified amount of fish oil that provided 1,080 mg of EPA and 720 mg of DHA per day for two months to achieve this result.¹²⁴ A double-blind trial found that the same amount of EPA and DHA plus 7.5 mcg per day of vitamin B12 led to a greater than 50% decrease in menstrual symptoms, but a group taking only fish oil did not obtain as much relief.¹²⁵ Six grams of fish oil per day provides the approximate levels of EPA and DHA used in these trials. In another double-blind trial, 1 gram per day of fish oil significantly decreased pain intensity, compared with a placebo, in women with dysmennorhea.¹²⁶

 

Animal research suggests that fish oils may reduce the severity of endometriosis,^127,128 and fish oils have been shown to improve symptoms of dysmenorrhea (painful menstruation),¹²⁹ which may be caused by endometriosis. Therefore, while no specific research has been done on the effects of fish oils in women with endometriosis, some health practitioners recommend several grams of fish oil per day for this condition.

Fish oil contains anti-inflammatory omega-3 fatty acids—primarily EPA and DHA— that may promote healthy metabolism by reducing insulin resistance and inflammatory signaling by adipose tissue.¹³⁰ Fish oil and omega-3 fatty acids appear to increase the sense of fullness improve the metabolic functions of fat tissue.¹³¹ One placebo-controlled trial enrolled 65 women with overweight or obesity, as well as depression; depression symptoms were reduced and weight loss was greater in those who received a combination of 1,080 mg of EPA and 720 mg of DHA daily after 12 weeks.¹³² A meta-analysis of data from eleven randomized controlled trials with a combined total of 617 participants found omega-3 fatty acids from fish can improve metabolic health by reducing waist circumference and triglyceride levels in individuals with overweight and obesity, but have little effect on weight loss.¹³³

 

Double-blind research shows that fish oil partially reduces reactions to allergens that can trigger attacks in some asthmatics.¹³⁴ Another double-blind study showed that fish oil supplements prevented exercise-induced asthma attacks in people with asthma.¹³⁵ A few other researchers have reported small but significant improvements when asthmatics supplement with fish oil,^136,137 but reviews of the research concluded that most fish oil studies showed little or no benefit.^138,139 It is possible that some of these trials failed to show an improvement because they did not last long enough to demonstrate an effect. There is evidence that children who eat oily fish may have a much lower risk of getting asthma.¹⁴⁰ Moreover, in a double-blind trial, children who received 300 mg per day of fish oil (providing 84 mg of EPA and 36 mg of DHA) experienced significant improvement of asthma symptoms.¹⁴¹ It should be noted that these benefits were obtained under circumstances in which exposure to food allergens and environmental allergens was strictly controlled. Though the evidence supporting the use of fish oil remains somewhat conflicting, eating more fish and supplementing with fish oil may still be worth considering, especially among children with asthma.

 

Preliminary¹⁴² and double-blind trials^143,144,145 have found that fish oil supplementation reduces inflammation, decreases the need for anti-inflammatory drugs, and promotes normal weight gain in people with UC. However, fish oil has not always been effective in clinical trials for UC.¹⁴⁶ Amounts used in successful clinical trials provided 3.2 grams of EPA and 2.2 grams of DHA per day—the two important fatty acids found in fish oil.

In a preliminary trial, people with UC significantly improved on a sugar-free, low-allergen diet with additional nutritional supplementation that included a multivitamin-mineral supplement (2–6 tablets per day); a fish oil supplement (400 mg per day); borage oil (400 mg per day); flaxseed oil (400 mg per day); and a probiotic formula containing Lactobacillus acidophilus and other species of beneficial bacteria.¹⁴⁷ Some participants received slight variations of this regimen. Since so many different supplements were given and since the trial was not controlled, it is not possible to say which, if any, of the nutrients was responsible for the improvement observed by the researchers.

 

Inflammation within the gut occurs in people suffering from Crohn’s disease. EPA and DHA, the omega-3 fatty acids found in fish oil, have anti-inflammatory activity. Though research is conflicting, there is some evidence that fish oil improves Crohn's disease symptoms. A two-year trial compared the effects of having people with Crohn’s disease eat 3.5 to 7 ounces of fish high in EPA and DHA per day or having them eat a diet low in fish.¹⁴⁸ In that trial, the fish-eating group had a 20% relapse rate compared with 58% among those not eating fish. Salmon, herring, mackerel, albacore tuna, and sardines are all high in EPA and DHA.

In a double-blind trial, people with Crohn’s disease who took supplements providing 2.7 g of EPA/DHA per day had a recurrence rate of 26% after one year, compared to a 59% recurrence rate among those taking placebo.¹⁴⁹

 

Supplementation with fish oil (providing either 2.7 g or 6.1 g per day of the omega-3 fatty acids EPA and DHA) significantly reduced recurrence of premature delivery, according to data culled from six clinical trials involving women with a high risk for such complications.¹⁵⁰ Fish oil supplementation did not prevent premature delivery of twin pregnancies, nor did it have any preventive effect against intrauterine growth retardation or pregnancy-induced hypertension. Fish oils should be free of contaminants, such as mercury and organochlorine pesticides. Women who eat substantial amounts of certain types of seafood (e.g., swordfish, tuna) may be consuming contaminants that can increase the risk of brain and nervous system abnormalities in their offspring. Exposure to mercury and polychlorinated biphenyls (PCBs) was found to be increased in relation to maternal intake of seafood. Higher exposure to these toxic contaminants has been linked to an increased risk of deficits in the developing brains and nervous systems of the children.¹⁵¹

The DHA found in fish oil is essential for the development of the visual system in infants.¹⁵² In one double-blind study, 103 term infants were randomly assigned to receive either formula with no docosahexaenoic acid (DHA) or arachidonic acid (ARA) or formula supplemented with DHA and ARA at concentrations similar to those found in human milk, starting when they were six days old. Visual maturation was assessed by measuring sweep visual evoked potential at ages 6, 17, 26, and 52 weeks. At each age, the supplemented group measured better, which led researchers to conclude that long-term supplementation of infant formula with DHA and ARA in amounts typical in human milk may help enhance visual development during the first year of life.

 

Fish oil supplementation has been proposed to lower the incidence of preeclampsia.^153,154 However, controlled clinical trials suggest that fish oil does not reduce symptoms¹⁵⁵ or protect against preeclampsia.^156,157

 

The omega-3 fatty acids in fish oil—eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)—decrease inflammation. Supplementation with EPA and DHA has prevented autoimmune lupus in animal research.¹⁵⁸ In a double-blind trial, 20 grams of fish oil daily combined with a low-fat diet led to improvement in 14 of 17 people with SLE in 12 weeks.¹⁵⁹ Other studies also found that supplementing with 10 to 15 grams of fish oil per day,¹⁶⁰ or with the amount of EPA and DHA provided by 10 grams per day of fish oil,¹⁶¹ is beneficial for people with SLE. People wishing to take such a large amount of fish oil should first consult with a doctor.

 

Omega-3 fatty acids have anti-inflammatory properties,¹⁶² and animal studies suggest that supplementation with omega-3 fatty acids may improve recovery and prevent infection after surgery.^163,164 A controlled human trial found that intravenous nutritional formulas containing omega-3 fatty acids given post-operatively lowered the production of inflammatory chemicals compared with standard nutritional formulas.¹⁶⁵ Other human studies of omega-3 fatty acid-supplemented nutritional formulas used in surgery patients have included other supplemental nutrients as well and are discussed below.¹⁶⁶

Research on the effect of the omega-3 fatty acids that are abundant in some fish, fish oils, and flaxseed oil is conflicting. Liquid diets containing omega-3 fatty acids used in hospitals for critically ill people have been shown to improve immune function and reduce infections.¹⁶⁷¹⁶⁸ However, in one controlled study in healthy people, a low-fat diet improved or maintained immune function, but when fish was added to increase omega-3 fatty acid intake, immune function was significantly inhibited.¹⁶⁹

Supplementation with DHA (an omega-3 fatty acid found in fish oil) in healthy young men has been shown to decrease the activity of immune cells, such as natural killer (NK) cells, and to inhibit certain measures of inflammation in the test tube.¹⁷⁰ The anti-inflammatory effects of DHA may be useful in the management of autoimmune disorders; however, such benefits need to be balanced with the potential for increased risk of infections. Other studies suggest that increased oxidative damage might be the reason for the negative effects on the immune system sometimes caused by fish oil, and that increased intake of antioxidants, such as vitamin E, could correct the problem.¹⁷¹

Omega-3 fatty acids from fish are well known to reduce inflammatory immune activity and have beneficial effects in a range of autoimmune conditions. Observational research suggests higher levels during infancy and early childhood may be linked to lower risk of developing type 1 diabetes.¹⁷² One study done in Norway found that babies given cod liver oil regularly during the first year of life had a 26% lower risk of developing type 1 diabetes in childhood. However, not all studies have noted a connection between omega-3 fatty acids and type 1 diabetes risk, and some researchers have proposed the discrepancies may be explained by genetic factors affecting fatty acid metabolism.^173,174

Higher intake of EPA, an omega-3 fatty acids from fish, has been correlated with better preservation of pancreatic cells that produce insulin and long-term blood glucose control in youth with type 1 diabetes.^175,176 A small pilot trial found that supplementation with 630 mg of EPA and 330 mg of DHA (another omega-3 fatty acid from fish oil) per day improved blood glucose control in subjects with type 1 diabetes.¹⁷⁷ Furthermore, better omega-3 fatty acid status may be helpful in slowing the progression of diabetes-associated complications such as kidney dysfunction and nerve pain.^178,179

Although fish oil fatty acids generally have positive effects on triglyceride levels, some studies have found supplemental DHA can increase LDL- and total cholesterol, which may increase cardiac risk. For this reason, some doctors are wary of fish oil supplements for patients with type 1 diabetes and may recommend EPA-only supplements instead.¹⁸⁰

Fish oil and its polyunsaturated omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been widely studied for their potential metabolic benefits. Clinical trials have reported conflicting evidence, with some studies finding positive effects, some no effects, and some negative effects of fish oil consumption on markers of metabolic health in people with type 2 diabetes.¹⁸¹ Attempting to explain these inconsistencies, one analysis suggested omega-3 fatty acids may be more beneficial in women than men.¹⁸² Nevertheless, a large meta-analysis that pooled findings from 45 randomized controlled trials with a combined total of 2,674 participants with type 2 diabetes found an overall positive effect of omega-3 fatty acids from fish on levels of markers of systemic inflammation, triglycerides, total cholesterol, LDL-cholesterol, and VLDL-cholesterol levels, as well as a small but statistically significant positive effect on HbA1c.¹⁸³ Another meta-analysis of 17 studies with a total of 672 participants found omega-3 fatty acids from fish could improve insulin sensitivity in people with metabolic disorders, including type 2 diabetes.¹⁸⁴

 

Fish oil containing EPA and DHA has been reported to reduce the symptoms of migraine headache in a double-blind trial using 1 gram of fish oil per 10 pounds of body weight.^185,186 Fish oil may help because of its effects in modifying prostaglandins (hormone-like substances made by the body).

 

In a preliminary study, four patients with chronic fatigue syndrome reported an improvement in their symptoms after taking an essential fatty acid supplement daily for at least 12 weeks.¹⁸⁷ The amount used was 10 to 18 capsules per day, and each capsule contained 93 mg of eicosapentaenoic acid (EPA), 29 mg of docosahexaenoic acid (DHA), and 10 mg of gamma-linolenic acid. Because there was no placebo group in this study and, because fatigue often improves after treatment with a placebo, additional research is needed to confirm this report.