| Summaries of the latest research concerning the health benefits of fish and fish oil |
CONTENTS |
| Safety |
| General Health Benefits |
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Bioavailability and Daily Requirements
Fish oil deficiency in older people Their study involved 15 residents (7 male and 8 female) aged between 79 and 98 years. The EPA and DHA content of their meals, snacks, and supplements was determined by actual measurement in duplicate food and supplement samples. Their blood level of fatty acids was determined from fingertip prick blood samples. The average (mean) daily intake of EPA + DHA was only 121 mg (median of 53 mg/day). Also of interest was that the average ratio of omega-6 to omega-3 fatty acids was 6.8 to 1. Analysis of blood samples showed that EPA concentration amounted to only 0.7% of total fatty acids, while DHA concentration was 1.8% of total fatty acids, both well below desirable levels. Interestingly enough, only one study participant consumed more than 400 mg/day of EPA + DHA and this person was taking a fish oil supplement.
The researchers conclude that this particular group of retirement home residents did not receive anywhere near the
daily recommended amount of EPA + DHA through their habitual (government mandated) diet. They suggest that
fish oil supplementation be considered for residents of long-term care facilities since it would likely be impractical
and cost-prohibitive to provide the required amount through the regular serving of fish. It is also of interest, and
considerable concern, that the average intake of vitamin D (mean 190 IU/day), vitamin E (mean 7.5 IU/day), and
magnesium (mean 270 mg/day) were all below recommended dietary allowances (600 IU/day, 15 IU/day, and 400
mg/day respectively).
Net benefit of fish consumption Thus, it is not surprising that health authorities promote the frequent consumption of fish with the American Heart Association (AHA) specifically recommending that healthy people eat fish at least twice a week. The AHA also recommends that patients with heart disease consume at least 1000 mg of EPA + DHA every day. Unfortunately, it is becoming more and more apparent that fish consumption is not always beneficial. Gary Ginsberg and Brian Toal from the Connecticut Department of Public Health point out that many fish are now heavily contaminated with methylmercury, a highly toxic compound with profound deleterious effects on both the cardiovascular and nervous system. Many researchers have studied these adverse effects and a consensus has been arrived at as to just what amounts of methylmercury are likely to produce serious consequences. Similarly, many studies have been done to determine the minimum daily intakes of EPA + DHA needed to obtain significant benefits. The two Connecticut researchers have combined these findings into two models aimed at predicting the net health benefits of consuming particular fish and seafood. One model is concerned with determining the net benefit for adult men and women (in regard to heart disease), the other with determining the net benefits for pregnant women and infants.
The researchers looked at 13 fish and seafood specimens available fresh in Connecticut and 3 varieties of canned
tuna. They found that it was safe for adults to consume unlimited amounts of tilapia, pollack, flounder, cod, shrimp,
trout, herring, canned light tuna, and Atlantic salmon, although they warn that farmed salmon may not be desirable
due to concerns about its possible content of carcinogens. Swordfish and shark should be totally avoided and tuna
steak should be eaten no more than once a week. Canned white tuna (Albacore), halibut, sea bass, and lobster
can safely be eaten twice a week. Their recommendations for pregnant women and infants are somewhat more
restrictive in that consumption of canned light tuna and cod should be limited to twice a week and consumption of
canned white tuna, tuna steak, halibut, sea bass and lobster should be limited to once a week.
Recommendations for fish oil intake Researchers at the University of South Dakota believe it is time to issue an official recommendation for a minimum daily intake of EPA + DHA in the USA. They suggest that the minimum intake should be 400 – 500 mg/day of EPA + DHA. They point out that several other countries already have such recommendations with France specifying an intake of 500 mg/day of EPA + DHA (minimum 120 mg/day of DHA), the UK 450 mg/day, Australia and New Zealand 442 mg/day of EPA + DHA for men and 318 mg/day for women. Both the American and Canadian Dietetic Association recommend 500 mg/day with a minimum of 120 mg/day of DHA. The US FDA has set an upper limit of safe EPA + DHA intake at 3000 mg/day, so the 500 mg/day recommendation is well within generally accepted safe limits.
The researchers point out that some fish are very contaminated with methylmercury and should be consumed only
rarely if at all. Among the worst offenders are tile fish, king mackerel, shark and swordfish, but the FDA also warns
that albacore (white) tuna should be consumed no more than once a week by pregnant women. Finally, they
suggest that if the recommended EPA + DHA intake cannot be achieved by fish consumption, then fish oil
supplements may be used instead to achieve the recommended minimum target of 500 mg/day of EPA + DHA.
Emulsification of fish oils improves absorption The trial involved 14 women and 10 men who were randomized to receive a mixture of oils (either emulsified or non-emulsified) with their breakfast. The oil mixture contained 43% concentrated fish oil, 31% borage oil, and 26% flaxseed oil. The participants had blood samples drawn prior to breakfast and 1.5, 3, 4.5, 6, 7.5, and 9 hours after. Analyses of the blood samples showed that the absorption of EPA and DHA in the group receiving the non-emulsified oil was only 34% and 44% respectively of that observed for the group receiving the emulsified oil.
The experiment was repeated after a 20-day washout period (the emulsified group receiving non-emulsified oil and vice versa) with similar results. The researchers observed no difference in absorption for palmitic acid, stearic acid, oleic acid, or linoleic acid suggesting that the increased absorption observed with emulsification is limited to long-chain polyunsaturated fatty acids such as EPA and DHA. The authors conclude that pre-emulsification significantly improves the absorption of fish oils.
Fish oil versus flax oil
Polyunsaturated fatty acids don’t compete over benefits Researchers studied the links between various PUFA intakes and the incidence of coronary heart disease (CHD) in 45,722 men enrolled in the Health Professionals Follow-up Study. A reliable food-frequency questionnaire was given at the start and completed every four years to determine PUFA intakes. During the 14 years of follow-up, there were 218 sudden deaths, 1,521 nonfatal myocardial infarctions (MIs) and 2,306 total CHD events (combined sudden death, other CHD deaths, and nonfatal MI) among the participants. Dietary analysis showed that both seafood-derived long-chain and plant-derived intermediate-chain n-3 PUFA intakes were linked to a reduced CHD risk, regardless of n-6 PUFA intake. Men who consumed more than 250 mg seafood-based n-3 PUFA per day had a 40-50 per cent lower risk of CHD.
The researchers also looked at the relationship between seafood-based n-3 PUFAs and plant-based n-3
PUFAs. They found that when seafood-based n-3 PUFA intake is low (less than 100 mg per day), plant-
based n-3 PUFAs are particularly effective at reducing CHD risk. For every additional 1 g of plant-based n-3
PUFA per day, MI risk was reduced by 58 per cent and total CHD risk was reduced by 47 per cent. Contrary
to previous findings, this study found no links between overall CHD risk and intake of n-6 PUFAs. The
results suggest that a modest dietary intake of seafood (250 mg, equaling around 1-2 oily fish meals a week)
may lower the risk of CHD, irrespective of n-6 PUFA intake. The authors concluded that plant sources of
PUFAs are especially important in populations with limited access to, or consumption of seafood.
Alpha-linolenic acid and DHA
Dutch researchers now report that the conversion of ALA to DHA in vegans (strict vegetarians) is
negligible and that supplementation with ALA does not increase DHA levels significantly. Their trial
included 6 healthy men and 3 healthy women between the ages of 20 and 60 years who were adhering to
a vegan diet (no meat, fish, eggs or dairy products). The participants were randomized to receive either
2.01 grams of ALA (4 ml linseed [flax] oil) daily or 1.17 grams of gamma-linolenic acid (6 ml borage oil)
daily for a four-week period. This was followed by a four-week period during which all the participants
received both supplements. Blood samples were taken and analyzed for fatty acid content at the start of
the trial and after four and eight weeks. Neither the linseed oil nor the borage oil by themselves
increased blood levels of EPA or DHA, but their combination did produce a statistically significant, but
nevertheless negligible, increase in EPA and DHA in the cholesterol and triglyceride fractions of the
blood. The researchers point out that a clinical trial involving omnivores (meat and fish eaters) gave
similar results and conclude that ALA supplementation is not effective in increasing DHA levels
significantly.
Safety
Net benefit of fish consumption Thus, it is not surprising that health authorities promote the frequent consumption of fish with the American Heart Association (AHA) specifically recommending that healthy people eat fish at least twice a week. The AHA also recommends that patients with heart disease consume at least 1000 mg of EPA + DHA every day. Unfortunately, it is becoming more and more apparent that fish consumption is not always beneficial. Gary Ginsberg and Brian Toal from the Connecticut Department of Public Health point out that many fish are now heavily contaminated with methylmercury, a highly toxic compound with profound deleterious effects on both the cardiovascular and nervous system. Many researchers have studied these adverse effects and a consensus has been arrived at as to just what amounts of methylmercury are likely to produce serious consequences. Similarly, many studies have been done to determine the minimum daily intakes of EPA + DHA needed to obtain significant benefits. The two Connecticut researchers have combined these findings into two models aimed at predicting the net health benefits of consuming particular fish and seafood. One model is concerned with determining the net benefit for adult men and women (in regard to heart disease), the other with determining the net benefits for pregnant women and infants.
The researchers looked at 13 fish and seafood specimens available fresh in Connecticut and 3 varieties of canned
tuna. They found that it was safe for adults to consume unlimited amounts of tilapia, pollack, flounder, cod, shrimp,
trout, herring, canned light tuna, and Atlantic salmon, although they warn that farmed salmon may not be desirable
due to concerns about its possible content of carcinogens. Swordfish and shark should be totally avoided and tuna
steak should be eaten no more than once a week. Canned white tuna (Albacore), halibut, sea bass, and lobster
can safely be eaten twice a week. Their recommendations for pregnant women and infants are somewhat more
restrictive in that consumption of canned light tuna and cod should be limited to twice a week and consumption of
canned white tuna, tuna steak, halibut, sea bass and lobster should be limited to once a week.
Fish oils are safe!
Dr. Bays also addressed the question, “Do prescription and/or supplement omega-3 fatty acid products contain excessive vitamin or toxins, such as mercury, polychlorinated biphenyls, dioxin, or other contaminants, in sufficient concentrations to pose a potential health risk?” Again, his answer is negative. This conclusion is largely based on a 2006 ConsumerLab evaluation of 42 commercially available fish oil supplements. All but two were found to contain the amount of EPA and DHA stated on the label, were free of mercury, PCBs and dioxins, and were not oxidized (rancid). Among the brands that passed the ConsumerLab evaluation were Carlson, Coromega, Metagenics, Nordic Naturals, Kirkland and Puritan Pride. Dr. Bays cautions that a high fish oil intake through the consumption of large amounts of fish may present a risk for environmental toxin exposure, especially methylmercury, PCBs, organochlorine pesticides and dioxins. He points out that oxidized mercury is insoluble in oil, so would not be expected to represent a significant toxicity risk in fish oil supplements.
In an accompanying editorial Dr. William Harris of the University of South Dakota emphatically endorses Dr. Bays’ conclusion that fish oils do not increase bleeding risk even if taken in combination with aspirin or warfarin.
All fish are not equally healthy University of Quebec researchers now question the assumption that fish consumption is universally beneficial. They do not question whether an increased intake of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is beneficial – this has pretty well been proven beyond a doubt. However, they do question whether all fish actually ends up contributing to the body’s stores of EPA and DHA when consumed. Their study involved 243 moderate consumers of fish living in the areas surrounding four lakes in the province of Quebec. The participants were interviewed to determine their consumption of 12 freshwater and 30 marine (saltwater) fish over the preceding three months and then had blood samples drawn for the determination of fatty acid (especially EPA and DHA), mercury, and selenium content. The age of the participants ranged between 18 and 74 years, 53% were men and 26% were considered obese (BMI >30). No relation was observed between fish intake and BMI, or between fish intake and alcohol intake. The 243 participants were divided into 4 groups according to daily consumption (occasional – < 24 grams/day, low – 24-41 grams/day, moderate – 41-66 grams/day, and high – > 66 grams/day). The average (mean) estimated intake of DHA + EPA from fish was 223 mg/day and that of omega-6 fatty acid (from fish) was 95 mg/day giving a very healthy ratio of omega-6 to omega-3 of 0.32. Much to their surprise, the researchers found no correlation between the total intake of fish or the intake of locally caught fish and serum levels of EPA and DHA. They did, however, find a strong correlation between the intake of salmon and trout and serum levels of EPA and DHA.
They conclude that, even though food tables may show that some lean fish do contain EPA and DHA, for some reason consuming these fish does not increase serum levels of EPA and DHA. Thus, the advice to eat fish on a regular basis needs to be revised to apply to only saltwater fish (especially salmon, mackerel, trout, sardines, and herring). The researchers also noted an increased blood methylmercury concentration in frequent fish eaters. They conclude that no matter how many locally caught freshwater fish are eaten, serum EPA + DHA levels are not affected.
Fish intake—Risks and benefits This paper quotes a number of studies that relate to undesirable intakes of organic mercury for women of childbearing age, nursing mothers, and young children, but it is hard to believe that the limits are more than a rough estimate. The situation with regard to health effects of trace amounts of mercury on adults is even less clear-cut. There are reports of adverse effects of mercury on cardiovascular and neurologic health. As regards the former, the authors simply pose the question as to whether the expected benefits from fish consumption would merely be greater if mercury were not present. As regards the neurologic aspect, the evidence as to adverse effects is unclear but there is a growing body of evidence that fish consumption may favorably influence clinical neurologic outcomes in adults, including benefits associated with ischemic stroke, cognitive decline and dementia, depression and other neuropsychiatric disorders. Translated into a useful guideline, the end result is advice not to eat shark, swordfish, golden bass and king mackerel since they typically contain more than 50 micrograms of organic mercury (methylmercury) per serving. Levels of dioxins and PCBs are low in fish and the authors take the position, based on what evidence is available, that any adverse effects from these contaminants are outweighed by the benefits of eating fish. Fish are also a rich dietary source of selenium and the authors mention evidence that some of the adverse effects of organic mercury may be mitigated by adequate intake of selenium, which incidentally is an essential dietary trace element. The bottom line is that the following fish pass muster as being good sources of EPA and DHA and are on average low in mercury: anchovies, Atlantic herring, wild and farmed salmon, sardines, and trout. These fish provide between 600 and 4500 mg per serving of EPA + DHA and contain on average 0.7 or less parts per million of mercury.
The authors also discuss plant sources of EPA and DHA. These two long-chain omega-3 fatty acids in fact do not occur in plants, but must be made in the body from alpha-linolenic acid which is present in flaxseed, canola, soybeans and walnuts. Only small amounts are converted to EPA and further conversion to DHA limited. Thus fish represent by far the best source, and the authors raise no objections to getting these fatty acids from fish oil capsules, which typically contain 20% DHA and 80% EPA with little or no mercury, and taking even 1-3 grams of fish oil, according to the authors, results in low intake of PCB and dioxins.
Polyunsaturated fatty acids are safe
Dr. Jan Eritsland, a cardiologist at the Ulleval University Hospital, has just released a major study dealing
with the safety of n-3 and n-6 PUFAs. Based on numerous reports published in the medical literature Dr.
Eritsland concludes that a high intake of n-3 PUFAs reduces the risk for cardiovascular disease and heart
attack and is entirely safe at least up to a level corresponding to 10% of the daily calorie intake. He does
caution though that the intake of dietary antioxidants (especially vitamin E) needs to be increased if the
PUFA intake is increased. Supplementation with 4 grams/day of highly concentrated fish oil (containing
3.4 g of EPA and DHA) was found to lower triglyceride levels, but had no effect on cholesterol levels or
glycemic control (plasma glucose and insulin levels). Although fish oils are known to reduce the tendency
of blood to aggregate (clot) a recent major trial showed no difference in bleeding episodes among heart
disease patients supplementing with 2 to 5 grams/day of fish oils and the controls. This held true even if
the patients were also taking warfarin or aspirin. PUFAs of the n-3 family may help prevent cancer and
there is no evidence at all that they promote it. There is, however, some limited evidence that n-6 PUFAs
(linoleic acid) may indeed be involved in the initiation or promotion of cancer. Most experts recommend
that the intake of linoleic acid not exceed 10% of daily calorie intake. [73 references]
General Health Benefits
Net benefit of fish consumption Thus, it is not surprising that health authorities promote the frequent consumption of fish with the American Heart Association (AHA) specifically recommending that healthy people eat fish at least twice a week. The AHA also recommends that patients with heart disease consume at least 1000 mg of EPA + DHA every day. Unfortunately, it is becoming more and more apparent that fish consumption is not always beneficial. Gary Ginsberg and Brian Toal from the Connecticut Department of Public Health point out that many fish are now heavily contaminated with methylmercury, a highly toxic compound with profound deleterious effects on both the cardiovascular and nervous system. Many researchers have studied these adverse effects and a consensus has been arrived at as to just what amounts of methylmercury are likely to produce serious consequences. Similarly, many studies have been done to determine the minimum daily intakes of EPA + DHA needed to obtain significant benefits. The two Connecticut researchers have combined these findings into two models aimed at predicting the net health benefits of consuming particular fish and seafood. One model is concerned with determining the net benefit for adult men and women (in regard to heart disease), the other with determining the net benefits for pregnant women and infants.
The researchers looked at 13 fish and seafood specimens available fresh in Connecticut and 3 varieties of canned
tuna. They found that it was safe for adults to consume unlimited amounts of tilapia, pollack, flounder, cod, shrimp,
trout, herring, canned light tuna, and Atlantic salmon, although they warn that farmed salmon may not be desirable
due to concerns about its possible content of carcinogens. Swordfish and shark should be totally avoided and tuna
steak should be eaten no more than once a week. Canned white tuna (Albacore), halibut, sea bass, and lobster
can safely be eaten twice a week. Their recommendations for pregnant women and infants are somewhat more
restrictive in that consumption of canned light tuna and cod should be limited to twice a week and consumption of
canned white tuna, tuna steak, halibut, sea bass and lobster should be limited to once a week.
Review supports benefits of omega-3 fatty acids for prevention of heart disease Now, researchers from Emory University School of Medicine have reviewed the data from randomized controlled clinical trials on n-3 PUFAs and CHD. The studies were divided into those using plant-based n-3 PUFAs (alpha-linolenic acid, ALA), fish-based n-3 PUFAs (eicosapentaenoic acid, EPA, and docosahexaenoic acid, DHA), and fish consumption in the diet. Fourteen randomized clinical trials were included in the review, six of which were of fish oil, including one large trial of 10,000 participants. The researchers report a clear trend suggesting that there are important differences in CHD outcomes when using fish-based EPA or DHA compared with plant-based ALA. Most of the fish oil trials suggest a significant reduction in total mortality and CHD deaths and a possible strong antiarrhythmic effect. The dietary fish trials also suggest a reduction in mortality and reduced arrhythmia, supporting the theory that fish-based n-3 PUFAs may impart their cardioprotective effect by acting as an antiarrhythmic agent. They may do so by stabilizing the electrical activity of heart muscle cells or by decreasing the heart rate. The trials of ALA supplements and ALA-enriched diets, including walnut, soybean, or flaxseed oil, were less reliable, but showed possible benefits in reducing mortality.
The review concludes that the evidence suggests a role for fish oil (EPA, DHA) or fish in
secondary prevention, as clinical trial data demonstrate a significant reduction in total mortality,
coronary heart disease death, and sudden death. However the data on ALA is limited by studies
of limited quality. Several previous studies have suggested that n-3 PUFAs reduce heart attack
risk through benefiting endothelial function (cells of blood vessel walls), reducing inflammation,
and the risk of thrombosis (blood clotting). The American Heart Association has published
guidelines for patients with CHD recommending a consumption of fish and fish oil, totaling 1g/day
of EPA and DHA.
Fish oils benefit patients with lupus Their clinical trial involved 52 SLE patients who were randomly assigned to receive 3 grams/day of fish oil providing 540 mg/day of EPA (eicosapentaenoic acid) and 360 mg/day of DHA (docosahexaenoic acid), 3 mg/day of copper in the form of a copper di-glycinate amino acid complex, both fish oil and copper, or a placebo. The study lasted 24 weeks and participants were assessed at baseline, 6, 12 and 24 weeks.
The researchers found that disease activity at 24 weeks, as measured by the SLAM-R score, was
significantly
less in the groups that had supplemented with fish oil than in the placebo and copper only groups. They
conclude that supplementation with fish oil may be effective in favourably modifying the symptomatic
disease
activity in SLE.
Lifespan and fatty acids
Fish oils and the immune system
Their clinical trial involved 48 men and women aged 55 to 75 years. The participants were randomized to
receive one of six supplements for 12 weeks. The supplements were all provided in the form of capsules,
three of which were to be taken with each meal. The nine capsules (daily intake) contained either a total
of 2 g alpha-linolenic acid, 770 mg gamma-linolenic acid (from evening primrose oil), 680 mg arachidonic
acid, 720 mg docosahexaenoic acid (DHA), 720 mg eicosapentaenoic acid (EPA)+ 280 mg DHA (fish oil)
or a placebo (an 80:20 mix of palm and sunflower oils). All the participants had blood samples taken four
weeks before start of supplementation, immediately before start of supplementation, and then every four
weeks during the trial as well as after a four-week washout period. The researchers found no changes in
killer cell activity except in the group taking fish oil. Here they observed an average decline of 20 per cent
after 8 weeks and 48 per cent after 12 weeks. The decline was completely reversed after the washout
period. The fact that no decline was observed with pure DHA strongly suggests that EPA was
responsible. The researchers conclude that an excessive EPA intake could have adverse effects for
people at risk of viral infections and some cancers. Editor’s Note: The British researchers’
speculation about fish oils perhaps affecting the effectiveness of NK cells in killing cancer cells is at odds
with the results of many other studies. There are at least a dozen studies that show a clear protective
effect of fish or fish oil against breast, colon, and prostate cancer. NOTE: This study was partly funded by
Unilever. [54 references]
Fish oils are vital to your health Recent research has shown that the consumption of high fat meals can initiate the development of atherosclerotic deposits. This effect can be substantially reduced by taking fish oil prior to eating such meals. Omega-3 fatty acids are essential to fetal development and a deficiency of DHA during gestation can lead to visual impairment and perhaps, lower intelligence quotients.
In summary, omega-3 fatty acids and in particular, DHA and EPA from fish oils, are essential for human
development and in the prevention and amelioration of many common disorders. [38 references]
Benefits of essential fatty acids
Your brain needs DHA
Health benefits of fish oils
Role of fish oils in health and disease Dr. Simopoulos points out that omega-3 polyunsaturated fatty acids (PUFAs) are essential for human health, but that their intake has gradually declined over the years. It is believed that man evolved on a diet with a ratio of omega-6 to omega-3 PUFAs of about 1:1. Today this ratio is more like 10:1 and in some societies is approaching 25:1. A relative over-abundance of omega-6 PUFAs has been implicated in excessive blood clotting, allergic and inflammatory disorders, and certain cancers. An adequate intake of omega-3 PUFAs, on the other hand, has been linked to improved cardiovascular health. A recent study concluded that a daily intake of 500 to 1000 mg of long chain omega-3 PUFAs reduces the risk of cardiovascular death in middle-aged American men by about 40%. Other studies have shown that although fish oils help prevent undesirable blood clotting reactions they do not increase bleeding time and are quite safe even for people scheduled for major surgery. Animal studies have found that fish oil supplementation markedly reduces the risk of fatal arrhythmias. Fish oils have also been found beneficial in preventing or treating hypertension, arthritis, psoriasis, ulcerative colitis, cancer, and certain diabetes- related complications. EPA and DHA are both essential for pregnant mothers and infants and a deficiency can retard the development of the brain and retina.
It is estimated that the optimal daily intake of EPA and DHA (total) is about 300 to 400 mg/day. The
current average intake in the United States is only 50 mg EPA and 80 mg DHA per person per day
indicating a massive deficiency in the American diet. Dr. Simopoulos points out that the Canadian
Ministry of Health's guidelines for fatty acid intake recommends a daily intake of 1000 to 1800 mg of
omega-3 PUFAs. She cautions that fish oil supplements should always be stabilized with adequate
amounts of vitamin E in order to prevent oxidation leading to rancidity. [211 references]
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Additional References
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