Product Review: Fish Oil and Omega-3 Fatty Acid Supplements Review (Including Krill, Algae, and Calamari Oil)
||Initial Posting: 8/10/12 Last Updated: 1/31/14
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What It Is:
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are two principal fatty acids found in fish, krill, and calamari. They belong to a family of nutrients known as omega-3 fatty acids. EPA and DHA can also be obtained from other marine sources, such as algae (algal oil). EPA and DHA are polyunsaturated fats ("good" fats, as opposed to saturated fats which are thought to increase the risk of heart disease). The body can only manufacture limited amounts of EPA and DHA from the essential fatty acid, alpha-linolenic acid (ALA) -- found in flaxseed oil, canola oil, soy oil and walnut oil. For more information about ALA see the separate review covering ALA and GLA products.
What It Does:
Cardiovascular and Cerebrovascular Disease (Heart Attack and Stroke):
The omega-3 fatty acids EPA and DHA have a number of potentially heart-healthy effects, including reducing triglyceride levels, slightly raising levels of HDL ("good") cholesterol, possibly, "thinning" the blood, reducing levels of homocysteine, and reducing blood pressure. Increased consumption of fish oil (such as from eating fish) may help slow the progression of atherosclerosis, thereby preventing heart attacks, and reduce the risk of sudden death due to cardiac arrhythmias. These effects seem to have received further support from a 14-year study of generally healthy older people (average age of 74) (Mozaffarian, Ann Int Med 2013). Although none of the people in this study took fish oil supplements, higher blood levels of omega-3s were associated with decreased risk of dying during the study. In fact, those with the highest 20% in blood levels were 27% less likely to die than those in the lowest fifth, an improvement equal to an additional 2.2 years of life after the age of 65. Those with the higher omega-3 blood levels were also 40% less likely to have a heart attack and 48% less likely to die of an arrhythmia. The researchers indicated that the high blood levels could be achieved with average daily intake of a moderate amount of fish providing 250 mg to 400 mg of EPA plus DHA (see Getting EPA and DHA from Food, below) and noted that greater intake would not yield much further benefit.
Researchers have sought to determine if there is conclusive evidence to demonstrate that fish oil supplements
reduced the risk of strokes and heart attacks in people with a history of cardiovascular disease. A review of 14 studies (involving a total of 20,485 patients, each lasting 1 to 4.7 years and using 400 mg to 4,800 mg of EPA and/or DHA per day) found no significant difference in outcomes between those who took or didn't take fish oil supplements (Kwak, Arch Intern Med 2012
). Earlier research suggested a benefit for these patients, as well as for healthy individuals. Clinical trials since 2010, however, cast some doubt on this benefit for both groups — although it has been noted that these studies may have been too short or small to detect small or modest benefits (Hu, Arch Intern Med 2012
). Similarly, a study of diabetics and others with poor glucose control and a history of cardiovascular disease found no reduction in cardiovascular events among those who received 900 mg of EPA and DHA daily for about 6 years compared to those who received placebo (olive oil), despite a significant (14.5 mg) decrease in triglycerides (Bosch, NEJM 2012
). A potential beneficial effect of the fish oil may have been masked by the fact that participants continued to take other heart medications and already had a median intake of 210 mg of omega-3 fatty acids from their diets. Additionally,the "placebo" used was olive oil, which may also have heart-related benefits.
A systematic review of 20 studies published from 1989 to 2012 (involving a total of 68,680 patients, each lasting from 1 to 6.2 years and using 270 mg to 6,000 mg of EPA and/or DHA per day from supplements) similarly concluded that supplementation with omega-3 fatty acids EPA and/or DHA was not associated with a lower risk of heart attack, stroke, cardiac death, sudden death or all forms of death among people, most of whom were at increased cardiovascular risk and many of whom were taking cardiovascular medication (Rizos, JAMA 2012
). Similarly, a study involving over 12,000 patients with multiple risk factors for heart disease found that taking a fish oil supplement daily (providing at least 850 mg of EPA and DHA, of which 47% to 60% was EPA) did not significantly reduce heart-related events such as heart attack or stroke compared to placebo (olive oil) (Roncaglioni, NEJM 2013). As in other studies, any benefit from fish oil could have been masked since many study participants were taking other heart medications and about 75% already consumed fish 1-3 times per week in their diets.
A study evaluating stroke found no benefit from fish oil supplementation, although there was benefit from dietary fish consumption. The analysis of 38 studies involving a total of nearly 800,000 people found that consuming 2 to 4 servings per week of fish was associated with a 6% lower risk of stroke compared to the consumption of one or fewer servings per week (Chowdhury, BMJ 2012). Five or more servings per week of fish had a 12% lower risk. The researchers concluded that this beneficial effect of fish intake is likely due to "a wide range of nutrients abundant in fish." Interestingly, the decreased risk of stroke was only seen with "fatty" fish types and not "white" fish types" -- although this may be explained by the fact that, in the populations studied, white fish types were typically served fried or deep fried
The bottom line on fish oil for cardiovascular and cerebrovascular disease:
- The most recent research does not support fish oil supplementation for preventing heart attacks or stroke in people who have heart disease or who are at risk for heart disease.
- Any potential cardiovascular benefit of supplementation may be limited to people who do not regularly consume fish in their diets and who are not taking other medications for heart disease.
- There is no reliable evidence that fish oil supplements prevent heart disease in healthy people who are not at risk for heart disease.
- Eating fatty fish twice per week as part of a healthy diet continues to be recommended.
Arthritis and Other Inflammatory Diseases:
Increased intake of the omega-3 fatty acids in fish oil alter the body's production of substances known as prostaglandins, and, consequently, reduce some forms of inflammation. On the basis of this, EPA and DHA have been tried in the treatment of symptoms of rheumatoid arthritis with considerable success (especially in early stages of the disease). Unlike "disease modifying" drugs, however, fish oil probably doesn't slow the progression of the disease. A study of several thousand women in Sweden found that consistent, long-term term intake averaging more than 210 mg per day of omega-3 fatty acids from eating fish was associated with a 52% lower risk of developing rheumatoid arthritis compared with lower intakes over the period of the study -- about 7.5 years (Di Giuseppe, Ann Rheum Dis 2013
). This level of intake is equal to at least one serving per week of a fatty fish, such as salmon, or four servings per week of lean fish, such as cod. The study could not adequately assess the impact of supplement use due to limited use of supplements in the study population.
The anti-inflammatory effects of EPA and DHA have also caused researchers to investigate possible benefits of fish oil for the treatment of menstrual cramps, inflammatory bowel disease (ulcerative colitis and Crohn's disease), lupus, and IgA nephropathy. For each of these conditions, at least one double-blind study has found positive results. A large European study (Hart 2009
) showed that people with the highest consumption of DHA (410 mg to 2,000 mg per day) had a 77% reduction in the risk of developing ulcerative colitis over an average period of four years than those consuming the lowest amount (up to 110 mg per day). Conversely, those consuming the most (15 to 35 grams per day) of linoleic acid (an omega-6 fatty acid) were 2.3 times as likely to develop the disease as those consuming the lowest amount (8 grams - 11 grams per day). However, in Crohn's disease, a trial of four grams per day of omega-3 fatty acids (50-60% EPA and 15-25% DHA) was ineffective at preventing relapses.
Symptoms of the inflammatory condition keratoconjunctivitis sicca (dry eye) have improved with taking a formula consisting of fish oil with black currant seed oil and other ingredients (Sheppard, Cornea 2013
Some evidence suggests that fish oil may reduce the risk of cancer of the colon/rectum and breast. The latest evidence relating to breast cancer comes from a prospective study of supplement use and breast cancer risk among postmenopausal women (Brasky, Canc. Epidemiol. Biomarkers Prev 2010
). Current use (but not past use) of fish oil supplements was associated with a 32% reduction in the risk of breast cancer. A specific dose or frequency of fish oil use associated with the greatest risk reduction was not determined. Risk was greatly reduced for ductal carcinoma of the breast (the most common form of breast cancer), but not lobular carcinoma. This risk reduction was not seen with other supplements commonly taken for menopausal symptoms (black cohosh
, dong quai
, or St. John's wort
). It is speculated that the anti-inflammatory property of fish oil may be responsible for an anti-cancer effect because chronic inflammation is associated with cancer initiation and progression. Researchers note, however, that fish oil cannot be recommended for breast cancer prevention without further study. (See the Review of Cancer Prevention Supplements
for information about other supplements used for cancer prevention.)
There is mixed evidence as to whether fish oil and omega-3 fatty acids help prevent prostate cancer. One study found no association between fish consumption and the development of prostate cancer although it found a large reduction in deaths from prostate cancer (Szymanski, Am J Clin Nutr 2010
). A 6-year study of men who self-reported taking fish oil supplements also found no association between fish oil use and the development of prostate cancer (Brasky, Nutr Cancer 2011
). However, some studies which did not look directly at the consumption of fish or fish oil but at the ratios of fatty acids in blood serum, have found some unexpected associations with prostate cancer: The most recently reported study of this kind found that men with the highest levels of DHA plus EPA and DPA (another omega-3 fatty acid) were 44% and 71%, respectively, more likely to develop low-grade and high-grade prostate cancers compared to men with the lowest levels (Brasky, JNCI 2013
). This report included an additional analysis of several other blood-based studies, most of which, but not all, also showed associations between fatty acids in fish oil (particularly DHA) and development of prostate cancer (particularly high-grade cancer). However, whether or not there is a cause-and-effect relationship between intake of fish oils and prostate cancer is still not known. A large study (the VITAL
study) using a highly concentrated fish oil supplement is underway to help address this question.
Fish oil may prevent weight loss during cancer chemotherapy. Although some trials have not shown a benefit, a recent study (Murphy, Cancer 2011
) showed significant benefit. In this study, patients with non-small cell lung cancer took fish oil throughout initial chemotherapy (approximately 10 weeks). During the course of chemotherapy, patients who did not take fish oil experienced an average weight loss of 5 lbs (of which approximately 2.2 lbs was muscle). Those taking fish oil had, on average, no change in weight despite having lost, on average, 6.3% of their weight over the previous 6 months. In fact, many of those taking fish oil increased their muscle mass — with the greatest increases corresponding to the greatest increases in plasma EPA concentrations. Cancer response rates to the chemotherapy were similar in the two groups. Patients taking the fish oil were given an option consuming either four 1 gram gelatin capsules per day or 7.5 mL of liquid fish oil per day. Both formulations provided 2.2 grams of EPA per day.
Analyses of dietary intakes taken as part of the Age-Related Eye Disease Study (AREDS) show that participants who reported the highest intake of EPA and DHA were 30% less likely to develop diseases of the retina -- neovascular age-related macular degeneration (AMD) and central geographic atrophy (CGA) -- compared to those with the lowest intake (SanGiovanni 2009
). Decreased risk of developing AMD was also shown in a study of over 30,000 female health professionals: Those consuming at least one serving per week of fish had a 42% reduction in risk of developing AMD compared to those eating less than one serving per month — and the benefit was greatest with canned tuna or dark-meat fish (e.g., mackerel, salmon, sardines, bluefish, and swordfish) (Christen, Arch Opthamol 2011
). Analyzed another way, the risk of developing AMD in this study was reduced by 38% and 36%, respectively, among those with the highest intakes from their diets of DHA (230 mg median intake) and EPA (100 mg median intake) compared to those consuming the least amount (median intakes of 60 mg of DHA and 10 mg of EPA). Based on these observations, EPA and DHA were included in the large AREDS2 (Age-Related Eye Disease Study 2) which evaluated a combination of supplements for preventing the progression of AMD. However, the addition of 350 mg DHA and 650 mg EPA to a combination vitamin A (from beta-carotene), vitamin C, vitamin E, zinc, and copper did not offer any additional benefits for slowing progression of AMD (AREDS2 Res Grp, JAMA 2013). See the Review of Eye Health Supplements for more information about AREDS and AREDS2.
Psychiatric and Mental Disorders:
For reasons that are less clear, omega-3s seem to help depression, bipolar disorder, and schizophrenia according to a limited number of double-blind trials. Fish oil has also been proposed for attention deficit disorder, borderline personality disorder, dyslexia and cognitive impairment, but supporting evidence for these uses remains preliminary.
A study of depressed older women in a nursing home setting showed that after taking high-dose omega-3 fatty acids for eight weeks (2,500 mg once daily consisting of 1,670 mg EPA and 830 mg DHA), 40.9% had a remission of depression compared to 16.7% of those taking placebo (Rondanelli, J Am Col Nutr 2010
). This study also found a statistically significant improvement in the self-assessed quality of life and that the fish oil treatment was well tolerated. In another study, the combination of EPA plus the prescription antidepressant fluoxetine (Prozac) was better than either EPA or fluoxetine alone for treating major depression in a short-term (8-week) study of 60 people. However, a study of people with congestive heart failure and depression failed to show any additional benefit from EPA (930 mg) and DHA (750 mg) daily when added to treatment with the prescription antidepressant sertraline (Zoloft) (Carney, JAMA 2009
The best evidence for omega-3's has been in cases of major and moderate depression, but not mild depression, and one group of researchers has concluded that the antidepressant benefit is strongly dependent upon the EPA content of the supplement. After pooling and reviewing studies using a total of 1,000 mg to 6,000 mg of EPA and DHA, those in which EPA was 60% or more of the total showed a highly significant improvement, whereas those that were less than 60% EPA did not (Martins, Molec Psy 2012). Other researchers, however, believe that any benefit is, at best, small to negligible (Bloch, Molec Psy 2012). Nevertheless, further analysis of blood samples from the study by Rondanelli (above) found that elderly depression is characterized by very low levels of omega-3s, in particular EPA, in red blood cell membranes compared to those in healthy individuals and that EPA-rich supplementation restored EPA concentrations to normal values (Rizzo, Nutr J 2012).
An analysis of blood samples from 1,600 military personnel showed those who committed suicide had, prior to suicide, significantly lower blood levels of DHA than personnel who did not commit suicide (Lewis, J Clin Psychiatry 2011
). The population studied was predominantly male and the risk of suicide was found to be 62% greater among men with levels of serum DHA below 1.75% (% of total serum fatty acids) compared to those with higher levels. There was no such relationship with EPA levels. The researchers note that omega-3 fatty acid levels were generally low across the military personnel in the study, much lower than in the general population, and suggested that even greater risk reductions could be possible with higher serum levels of DHA.
A study of U.S. medical students showed, over 12 weeks, that those who received high-dose omega-3 fatty acids (2,496 mg once daily providing 2,085 mg EPA and 348 mg DHA), had a 20% reduction in anxiety symptoms compared to those receiving placebo treatment. Treated students also had a 14% decrease in a marker of inflammation (stimulated IL-6 production) (Kiecolt-Glaser, Brain Behav Immun 2011
). The study intentionally used an extremely concentrated fish oil (supplied by OmegaBrite) high in EPA due to evidence that EPA has relatively stronger anti-inflammatory and antidepressant effects than DHA.
Fish oil may slightly blunt some responses to mental stress, according to a study of young men and women given a large amount of fish oil (9 grams daily providing 1,600 mg EPA and 1,100 mg DHA) for eight weeks. When the participants were asked perform math calculations as quickly as possible for 5 minutes (a mental stress test), the mean heart rate increased by 3 beats less per minute after fish oil therapy than when the test had been taken at the beginning of the study, before therapy. The increase in total nervous activity (measured by nerve activity in the leg) was also significantly less after fish oil therapy. A control group, given olive oil instead of fish oil, did not have these reductions in heart rate and nervous activity (Carter, Am J Physiol 2013).
DHA is important for normal development and functioning of the brain and retina in the fetus and in infants. For this reason, it is thought that pregnant or nursing mothers may benefit from supplementation. DHA is also often added to formula for premature infants and some regular infant formulas and foods. In a recently reported Australian study, pregnant women were given 800 mg of DHA and 100 mg of EPA daily (from 1500 mg of fish oil in capsules) until birth. Compared to women given placebo (vegetable oil capsules), there was no statistically significant increase in cognitive or language development in offspring during early childhood. Somewhat fewer of the treated women had postpartum depression (9.67%) than those who received placebo (11.19%), but this was not statistically significant. However, there was a significant decrease in very premature births (1.09% in the treated group vs. 2.25% in the placebo group) as well as fewer low birth weight infants and fewer admissions to neonatal intensive care units. There were also fewer fetal/infant deaths among those taking fish oil, although not by a statistically significant margin. At the same time, more of the treated women were induced or had cesarean sections because they were post term (Makrides, JAMA 2010
). Babies born to women in the study were nearly 40% less likely to have egg allergies in their first year of life. They were also less likely to have eczema, although this association did not hold after the results were adjusted for factors such as maternal history of allergies (Palmer, BMJ 2012
). A related editorial recommended that pregnant women should get 200 mg of DHA per day either from a supplement or low-mercury fish and that the benefit of higher intakes remains unclear (Oken, JAMA 2010
). Infants born to women in Mexico given 400 mg DHA daily (from algal oil from Martek Biosciences) during pregnancy (starting at about 20 weeks) had a lower occurrence of colds during the first three month of life than those whose mothers received placebo treatment (37.6% vs. 44.6%, respectively) (Imhoff-Kunsch, Pediatrics 2011
). However, median daily intake of DHA among pregnant women in Mexico is much lower than in the U.S. (80 mg vs. 100 to 200 mg, respectively), so the findings may not apply to groups already consuming higher amounts of DHA.
Population studies suggest that consumption of DHA is associated with reduced incidence of Alzheimer disease and animal studies demonstrate that DHA intake reduces Alzheimer-like brain disease. However, a recent study showed that supplementation with DHA from algae did not slow cognitive and functional decline in individuals with mild to moderate Alzheimer disease (Quinn, JAMA 2010
). There was also no apparent reduction in the decline in brain volume. In the study, patients received 2 grams of DHA from algal oil daily or placebo for 18 months. All of the patients had previously consumed less than 200 mg of DHA per day and had not taken supplements with DHA or EPA. Among those given DHA in the study, plasma levels of DHA tripled and the amount of DHA in cerebrospinal fluid increased by 38%, with no significant change in those taking placebo. It should be noted that the study did not assess whether DHA could play a preventative role in Alzheimer disease, nor did it assess the effect of DHA in conjunction with EPA.
A placebo-controlled, 1-year pilot study of 34 adults with mild to moderate impairment from Alzheimer disease found that alpha-lipoic acid and fish oil slowed the decline in subjects' cognitive functioning. The combination also slowed the decline in subjects' abilities to perform daily activities, as did fish oil alone, but not alpha-lipoic acid alone. The participants normally ate fish no more than once per week and most continued to take Alzheimer's medications. A capsule of alpha-lipoic acid (600 mg) was taken each morning along with 2 fish oil capsules (each containing 1 gram of fish oil, providing 325 mg EPA and 225 mg DHA in the triglyceride form). Another fish oil capsule was taken with lunch (Shinto, J Alzheimers Dis 2014). Although earlier studies, such as that above, have not shown a benefit with omega-3 fatty acids in Alzheimer's disease, this study differed in that the fish oil had a high ratio of EPA to DHA.
Age-related Cognitive Decline:
Studies have shown modest benefit with DHA for people with age-related cognitive decline (ARCD). Unlike Alzheimer disease, ARCD is not considered a disease and is a more gradual and, perhaps, normal consequence of aging. A 6-month study of people over age 65 with mild cognitive impairment showed that those receiving daily fish oil containing a large amount of DHA (1,550 mg) with EPA (400 mg) improved scores on verbal fluency (although not on any other memory or cognition test) compared to those in a control group receiving safflower oil (containing the omega-6 fatty acid, linoleic acid). An EPA/DHA combination (1,670 mg EPA with 160 mg DHA) did not affect any aspect of cognition or memory. However, both the EPA/DHA combination and, to a slightly greater extent, the DHA/EPA combination reduced depressive symptoms in these mildly cognitively impaired individuals (Sinn, Br J Nutr 2011
). The researchers note that depression is a potential risk factor for progression to dementia, so the reduction of depressive symptoms may reduce the risk of dementia. In another study (Yurko-Mauro, Alzheimer's & Dementia 2010
), participants with ARCD were given 900 mg per day of DHA from algal oil or placebo for 24 weeks. Those taking DHA showed significant improvements in verbal recognition memory, but no improvement in working memory or on executive function tests. Plasma DHA levels doubled in the group receiving the supplementation.
Memory-enhancement in Healthy Individuals:
In a small study of healthy, young adults, better working memory performance has been found to correlate with higher levels of DHA (as measured in red blood cell membranes), but not EPA (Narendran, PLoS One 2012). Working memory performance was tested by showing a series of letters and numbers and asking what appeared one, two, and three times prior. Those who had higher DHA levels performed better on the "3-back" question than those with lower levels. The subjects were then asked to take 2 grams of highly-concentrated fish oil (Lovaza, 930 mg EPA and 750 mg DHA) daily for six months and tested again: Scores improved on the "3-back" question and those who previously had the lowest DHA levels improved the most. Similarly, another 6-month study in healthy young adults with diets low in omega-3 fatty acids found those given a DHA-rich fish oil supplement daily (2,250 mg of fish oil providing 1,160 mg of DHA and 170 mg EPA) had improved memory performance compared to those who received placebo (Stonehouse, Am J Clin Nutr 2013). Specifically, women had greater improvements in episodic memory -- correctly remembering one more word or picture, while men experienced greater improvements in reaction times of working memory -- completing tasks 20% faster than men in the placebo group. The report notes that 6 months was chosen as the study period as this is required for DHA levels in tissue to plateau.
A placebo-controlled study in 65 healthy adults ages 50 to 75 years, found that taking fish oil for 6 months resulted in a 26% increase in executive functioning (e.g., verbal fluency, visual tasks, reading ability). There was no overall improvement in memory, although there was an improvement in memory consolidation -- the recall of words after a 30-minute delay. Those who took the fish oil also had significant gains in the structure and volume of tissue in several areas of the brain, improvements in the lining of the carotid artery, and a mean 3.4% reduction in diastolic blood pressure. The participants took 4 fish oil capsules daily, each containing 1,000 mg of fish oil (300 mg EPA and 220 mg DHA) which included 15 mg of vitamin E as preservative, and continued eating their normal diet, with most consuming fish one time per week (Witte, Cereb Cortex 2013).
Strength Training in Older Women:
A small study in Brazil looked at the potential benefit of fish oil on strength training in older individuals, based on the fact that omega-3's play a role in the plasma membrane and cell function of muscles (Rodacki, Am J Clin Nutr 2012
). Forty-five mostly sedentary women in their mid-60s were given two doses a day of a gram of fish oil containing 180 mg of EPA and 120 mg of DHA. After twelve weeks of supervised lower-body resistance-training (3 times per week), the strength of those taking the fish oil had improved more than those who did not supplement. Functional capacity (e.g., the speed of rising from a chair) also increased more among those who took fish oil. There was no improvement in the strength of women who took fish oil without strength training, and taking fish oil for two months before
training started did not confer added benefit.
Protection from Effects of Air Pollution
A small study by scientists at the U.S Environmental Protection Agency (EPA) in middle-aged people found that fish oil supplementation protected against adverse cardiac and lipid effects associated with air pollution exposure (Tong, Env Health Perp 2012). Participants in the study were given daily capsules of fish oil (3 grams, providing 1230 mg EPA and 822 mg DHA) or olive oil for four weeks and then exposed to air containing particles for two hours. This caused the group talking olive oil to experience undesirable changes in blood lipids (increased LDL and triglyceride levels), but this did not occur in the fish oil group. The fish oil group also experienced less negative effects on heart functioning than the olive oil group.
Other proposed uses of fish oils with some support include asthma, Raynaud's phenomenon (abnormal sensitivity of hands and feet to cold), chronic fatigue syndrome, cystic fibrosis, and osteoporosis.
The balance of current evidence suggests that fish oil is not effective for migraine headaches, psoriasis, male infertility and enhancing immunity in people with HIV. Although some research has indicated that omega-3 fatty acid supplements might have anti-inflammatory effects that could benefit patients with multiple sclerosis (MS), a placebo-controlled study of 92 MS patients found no beneficial effect with daily fish oil (1,350 mg EPA and 850 mg DHA) for 2 years whether taken alone (for 6 months) or in combination with interferon (for 18 months). (Torkildsen, Arch Neurol 2012
Fish oil supplements are commonly given to pets to help maintain their coats and skin. [Reviews of other pet supplements by ConsumerLab.com include ALA and GLA
, Joint Supplements
For information on dosages see What to Consider When Using.
Quality Concerns and What CL Tested for:
Because omega-3 fatty acids are obtained from natural sources, levels in supplements can vary, depending on the source and method of processing.
Contamination has also been an issue, because fish can accumulate toxins such as mercury, dioxins, and polychlorinated biphenyls (PCBs). Mercury can damage the nervous system -- particularly in a fetus. Dioxins and PCBs may be carcinogenic at low levels of exposure over time and may have other deleterious effects.
The freshness of the oil is also an important consideration because rancid fish oils can have an extremely unpleasant odor and taste. While you can sometimes determine this yourself if you take fish oil directly as a liquid, it can be masked by added flavors and not readily detected if you use a softgel and other encapsulated product. There may be safety considerations with rancid fish oils due to a variety of compounds produced, some of which are odorless, such as peroxides. A study commissioned by the government of Norway (where fish oil supplement use is extremely high) concluded there would be some health concern related to the regular consumption of oxidized (rancid) fish/marine oils, particularly in regards to the gastrointestinal tract, but there is not enough data to determine the risk (The Norwegian Scientific Committee for Food Safety, 2011
). The study explained that the amount of spoilage and contamination in a supplement depends on the raw materials and processes of extraction, refining, concentration, encapsulation, storage and transportation. However, it saw no significant risk of contamination by microorganisms, proteins, lysophospholipids, cholesterol, and trans-fats.
Additionally, some capsules are enteric-coated and are expected to release the oil after
the stomach to theoretically reduce fishy aftertaste or burp. If they release too soon they lose that potential benefit. If they release too late, the oil may not get absorbed.
Neither the FDA nor any other federal or state agency routinely tests fish or marine oil supplements for quality prior to sale. ConsumerLab.com, as part of its mission to independently evaluate products that affect health, wellness, and nutrition, purchased many dietary supplements sold in the U.S. claiming to contain EPA and/or DHA and tested them for their levels of omega-3 fatty acids (EPA, DHA and, if listed, ALA), mercury, lead, PCBs, and signs of decomposition. Enteric-coated capsules were tested to see if they properly released their ingredients. One product was additionally tested for dioxins at the request of its manufacturer. Among the products purchased and tested, the majority was for use by people and a few were for use by pets. Most of the supplements were softgel capsules or liquids.
For more information about the testing, see How Products Were Evaluated.
The distributor of one of the products which failed testing in this review has notified ConsumerLab.com that it has updated the labeling of the product. See the Update in the full review for details.