What’s not so Fishy about
Fish Oil & Omega 3 Fatty Acids
Vitamins 101
Dietary sources of omega-3 fatty acids include fish oil and certain
plant/nut oils. Fish oil contains both docosahexaenoic acid (DHA)
and eicosapentaenoic acid (EPA), while some nuts (e.g., English
walnuts) and vegetable oils (e.g., canola, soybean, flaxseed/
linseed, and olive oil) contain alpha-linolenic acid (ALA) [1].
Evidence from several studies has suggested that amounts of DHA and EPA in the form
of fish or fish oil supplements lowers triglycerides, slows the buildup of atherosclerotic
plaques (“hardening of the arteries”), lowers blood pressure slightly, as well as reduces
the risk of death, heart attack, dangerous abnormal heart rhythms, and strokes in people
with known heart disease.
The American Heart Association (AHA) states omega-3 fatty acids benefit the heart of
healthy people, and those at high risk of, or who have, cardiovascular disease [2]. However, high doses may have harmful effects, such as an increased risk of bleeding. Although similar benefits are proposed for alpha-linolenic acid, scientific evidence is less
compelling, and beneficial effects may be less pronounced [1].
Some species of fish carry a higher risk of environmental contamination, such as with
methylmercury. In addition, special care should be taken when purchasing nurtritional
supplements. Consumers should be warned to purchase pharmaceutical grade fish oils
and omega fatty acids.
Increasing omega-3 fatty acid intake through foods is preferable. However, people may
want to talk to their doctor about taking a supplement. Supplements also could help
people with high triglycerides, who need even larger doses. The availability of highquality omega-3 fatty acid supplements, free of contaminants, is an important prerequisite to their use [2].
The AHA recommends eating fish (particularly fatty fish) at least two times a week. Fish
is a good source of protein and doesn’t have the high saturated fat that fatty meat products do. Fatty fish like mackerel, lake trout, herring, sardines, albacore tuna and salmon
are high in two kinds of omega-3 fatty acids, eicosapentaenoic acid (EPA) and
docosahexaenoic acid (DHA).
The AHA also recommends eating tofu and other forms of soybeans, canola, walnut and
flaxseed, and their oils. These contain alpha-linolenic acid (LNA), which can become
omega-3 fatty acid in the body. The extent of this modification is modest and controversial, however[1]. More studies are needed to show a cause-and-effect relationship
between alpha-linolenic acid and heart disease.
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The table below is a good guide to use for consuming omega-3 fatty acids.
Summary of AHA Recommendations for Omega-3 Fatty Acid Intake [2]
Population
Patients without documented coronary heart disease (CHD)
Recommendation
Eat a variety of (preferably fatty) fish at least twice a week.
Include oils and foods rich in alpha-linolenic acid (flax
seed, canola and soybean oils; flaxseed and walnuts).
Patients with documented CHD
Consume about 1 g of EPA+DHA per day, preferably from
fatty fish. EPA+DHA in capsule form could be considered
in consultation with the physician.
Patients who need to lower triglycerides
2 to 4 grams of EPA+DHA per day provided as capsules
under a physician’s care.
Patients taking more than 3 grams of omega-3 fatty acids from capsules should do so only under a
physician’s care. High intakes could cause excessive bleeding in some people [1].
Background
In 2002, the AHA released a scientific statement, “Fish Consumption, Fish Oil, Omega-3 Fatty Acids and
Cardiovascular Disease,” on the effects of omega-3 fatty acids on heart function (including antiarrhythmic
effects), hemodynamics (cardiac mechanics) and arterial endothelial function. The link between omega-3
fatty acids and CVD risk reduction are still being studied, but research has shown that omega-3 fatty
acids
•
•
•
•
decrease risk of arrhythmias, which can lead to sudden cardiac death
decrease triglyceride levels
decrease growth rate of atherosclerotic plaque
lower blood pressure (slightly) [2]
What do epidemiological and observational studies show?
Epidemiologic and clinical trials have shown that omega-3 fatty acids reduce CVD incidence. Largescale epidemiologic studies suggest that people at risk for coronary heart disease benefit from consuming omega-3 fatty acids from plants and marine sources.
The ideal amount to take isn’t clear. Evidence from prospective secondary prevention studies suggests
that taking EPA+DHA ranging from 0.5 to 1.8 grams per day (either as fatty fish or supplements) significantly reduces deaths from heart disease and all causes. For alpha-linolenic acid, a total intake of 1.5–3
grams per day seems beneficial [2].
Randomized clinical trials have shown that omega-3 fatty acid supplements can reduce cardiovascular
events (death, non-fatal heart attacks, non-fatal strokes). They can also slow the progression of atherosclerosis in coronary patients [2]. However, more studies are needed to confirm and further define the
health benefits of omega-3 fatty acid supplements for preventing a first or subsequent cardiovascular
event.
Grade*
Uses based on scientific evidence[3]
High blood pressure
Multiple human trials report small reductions in blood pressure with intake of omega-3 fatty
acid. DHA may have greater benefits than EPA. However, it may be necessary to take high
amounts of omega-3 fatty acids per day to obtain these health benefits, and high doses may
increase the risk of bleeding. Therefore, a qualified healthcare provider should be consulted
before starting treatment with fish oil supplements.
Hypertriglyceridemia (fish oil / EPA plus DHA)
There is strong scientific evidence from human trials that omega-3 fatty acids from fish or fish
oil supplements (EPA + DHA) significantly reduce blood triglyceride levels. Benefits appear to
be dose-dependent. Fish oil supplements also appear to cause small improvements in highdensity lipoprotein (“good cholesterol”); however, increases (worsening) in low-density lipoprotein levels (LDL/”bad cholesterol”) have also been observed. It is not clear if alpha-linolenic acid
significantly affects triglyceride levels.
Secondary cardiovascular disease prevention (fish oil / EPA plus DHA)
Several studies report that regular consumption of oily fish or fish oil/omega-3 supplements
reduces the risk of non-fatal heart attacks, fatal heart attacks, sudden death, and deaths due
to any cause in people with histories of heart attacks. Most patients in these studies were also
using standard heart drugs, suggesting that the benefits of fish oils may add to the effects of
other therapies.
Infant eye / brain development
Early evidence suggests that infants have improved problem solving skills but not memory if
their mothers consume DHA-containing functional foods during pregnancy. Other research
suggests that DHA supplementation during pregnancy plays an important role in the development of the visual system.
Inflammation
Research has shown that omega-3 fatty acids help reduce inflammation. Scientists believe that
their anti-inflammatory effects may help protect against heart disease.
Nutrition (in gastrointestinal disorders)
Early evidence suggests that omega-3 fatty acid supplements may be a good source of
nutrition for patients with Crohn’s disease or for those who need to be tube fed after abdominal
surgeries.
Pregnancy nutritional supplement
DHA has been found to be important for healthy pregnancies. Research shows that fish oil
supplementation from the 22nd week of pregnancy until delivery improves the amount of n-3 LCPUFA in the fetus and the mother.
Primary cardiovascular disease prevention (fish intake)
Several large studies of populations (called epidemiological studies) report a significantly lower
rate of death from heart disease in people who regularly eat fish. Other epidemiological research reports no such benefits. It is unclear if benefits only occur in certain groups of people,
such as those at risk of developing heart disease. Fish oil is also associated with improved
blood vessel functioning and decreased resting heart rate. Overall, the evidence suggests
benefits of regular consumption of fish oil.
Protection from cyclosporine toxicity in organ transplant patients
There are many studies of heart transplant and kidney transplant patients taking cyclosporine
(Neoral®), who received fish oil supplements. Most trials report improvements in kidney
function and reduced high blood pressure compared to patients not taking fish oil. Although
several recent studies report no benefits for kidney function, the weight of scientific evidence
favors the beneficial effects of fish oil.
Rheumatoid arthritis (fish oil)
Many studies report improvements in morning stiffness and joint tenderness with the regular
intake of fish oil supplements for up to three months. Fish oil has been shown to increase the
effects of anti-inflammatory medications, such as NSAIDs (such as ibuprofen). However,
because of weaknesses in study designs and reporting, better research is needed before a
strong favorable recommendation can be made.
*Key to grades
A: Strong scientific evidence for this use; B: Good scientific evidence for this use;
A
A
A
B
B
B
B
B
B
B
Synonyms
á-linolenic acid (ALA, C18:3n-3), alpha-linolenic acid, cod liver oil, coldwater fish, DHA,
docosahexaenoic acid, eicosapentaenoic acid, EPA, fish body oil, fish extract, fish liver oil, fish oil fatty
acids, halibut oil, long chain polyunsaturated fatty acids, mackerel oil, marine oil, menhaden oil, n-3 fatty
acids, n-3 polyunsaturated fatty acids, Omacor®, omega fatty acids, omega-3 oils, polyunsaturated fatty
acids (PUFA), salmon oil, shark liver oil, w-3 fatty acids [3].
References
1. Mayo Clinic. http://www.mayoclinic.com/health/fish-oil/ns_patient-fishoil. Retrieved on 5/8/09.
2. American Heart Association. http://www.americanheart. org/presenter.jhtml?identifier=4632. Retrieved on 5/08/09.
3. Medline Plus. http://www.nlm.nih.gov/medlineplus/druginfo/natural/patient-fishoil.html. Retrieved on 5/8/09.