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Fish Oil

Fish oil is a a source of omega-3 fatty acids. It reduces triglycerides, but does not seem to affect the rate of cardiovascular events. It seems to notably reduce the symptoms of depression and improve some painful, inflammatory conditions.

Our evidence-based analysis on fish oil features 839 unique references to scientific papers.

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Summary of Fish Oil

Primary Information, Benefits, Effects, and Important Facts

What is fish oil?

Fish oil is a common term used to refer to two kinds of omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These omega-3 fats are usually found in fish, animal products, and phytoplankton.

The fatty acids EPA and DHA are involved in regulating various biological processes such as the inflammatory response, various metabolic signaling pathways, and brain function.[2] They can be synthesized in the body from alpha-linolenic acid (ALA), but in small amounts for most people.

What are fish oil's benefits?

Fish oil causes a potent reduction in triglyceride levels,[3][4][4][5][6][7][8][9][10][11][12][13] and a more modest reduction in blood pressure in hypertensives.[5][13][14][15][16][17][18][19] Despite this, long-term trials haven't found a reduction in the rate of cardiovascular events.[20]

It appears to notably improve mood in people with major depression, though it's unclear if it has an effect in people with minor depression.[21] EPA, in particular, seems to be the most effective omega-3 fatty acid for this purpose which suggests that the effects of fish oil are due to reducing neuroinflammation. Its anti-inflammatory benefits also seem to extend to reducing the symptoms of systemic lupus erythematosus.[22][9][23][23][24][25][26] However, its benefits shouldn't be assumed to extend to inflammatory diseases in general.

What are fish oil's side effects and drawbacks?

Many fish oil supplements may contain harmful lipid peroxides (oxidized lipids that can damage cells), but it's unclear if this has notable consequences to health.[27]

What is the difference between fish oil and omega-3 fatty acids?

"Fish oil" refers to a solution of fatty acids where the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are dominant. Fish is by far the most common source for fish oil, hence the name, but an artificially manufactured EPA/DHA dominant mixture from any source could be considered fish oil. Typical fish oil can contain small amounts of other omega-3 fatty acids, usually DPA and fatty acids that don't belong to the omega-3 category. Alpha-linolenic acid (found most abundantly in nuts and seeds), is an omega-3 fatty acid that can be turned into EPA and DHA but is not itself a fish oil fatty acid.[28]

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Things To Know & Note

Also Known As

Eicosapentaenoic Acid, EPA, Docosahexaenoic Acid, DHA, Omega-3 fatty acids, Omega-3, Omega 3, N-3 Fatty Acids

Do Not Confuse With

Alpha-Linolenic Acid (the plant-based omega-3)

Goes Well With

  • Though fish oil is not a stimulant, it increases brain activity, so a stimulatory effect may be felt after supplementation

  • Most of fish oil's beneficial effects happen over a period of days and weeks, rather than immediately

  • Post-supplementation "fish burps" can be avoided by consuming fish oil with food, or freezing the capsules before supplementation

How to Take Fish Oil

Recommended dosage, active amounts, other details

Fish oil doses vary depending on the goal of supplementation. For general health, 250mg of combined EPA and DHA is the minimum dose and can be obtained via fish intake. The American Heart Association recommends 1g daily. If the goal of supplementation is to reduce soreness, a 6g dose, spread over the course of a day, will be effective.

Since fish oil is a combination of two different fatty acids, these numbers reflect a combined total. Total eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) consumption should come from a mix of real food and supplements. The more EPA and DHA is provided by the diet, the less supplementation is required.

Fish oil can be taken throughout the day. To minimize the "fish burp" taste, take fish oil with meals.

Pregnant women should increase their intake of DHA by at least 200mg a day, as long as there is no risk of elevated mercury levels.

Frequently Asked Questions about Fish Oil

Should I take Fish Oil if I am sick?
Can I eat flax seeds instead of fish or fish oil for omega 3s?
While there are omega 3s found in flax seed, it cannot be used by your body. Supplementing with algae can help provide DHA.
Does fish oil actually help heart health?
The sheer number of fish oil studies makes it hard to tell if supplementation helps heart health. A recent meta-analysis looked at only the largest randomized trials, and found no benefit.
5 nutrients that could lift your mood
Many foods can temporarily boost your mood simply because they’re delicious. But healthy foods also contain certain nutrients that may have a more direct and lasting effect on your well-being.
When should I take Vitamin D?
Vitamin D can be taken any time. As it is fat soluble, likely best to take it with a meal.

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Human Effect Matrix

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects fish oil has on your body, and how strong these effects are.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Notes
grade-a Strong Very High See all 44 studies
Fish oil, both EPA and DHA, are reference drugs for the purpose of reducing triglycerides with highly reliable reductions in the range of 15-30% (higher reductions seen in persons with higher baseline triglycerides)
grade-a Notable Very High See all 23 studies
Fish oil supplementation has been noted to be comparable to pharmaceutical drugs (fluoxetine) in majorly depressed persons, but this may be the only cohort that experiences a reduction of depression. There is insufficient evidence to support a reduction of depressive symptoms in persons with minor depression (ie. not diagnosed major depressive disorder)
grade-a Minor Very High See all 9 studies
Supplemental DHA above 300mg appears to be effective in reducing ADHD symptoms in children when supplemented
grade-a Minor Very High See all 8 studies
May decrease blood pressure in persons with high blood pressure, but does not appear to have efficacy in persons with normal blood pressure
grade-a Minor Very High See all 27 studies
Mixed evidence, but a possible increase in HDL-C is seen with fish oil supplementation in unhealthy persons
grade-a Minor Moderate See all 17 studies
Highly mixed and unreliable influences on circulating inflammatory cytokines (although, due to immunosuppression on cellular adhesion factors, the overall effect may still be antiinflammatory)
grade-a
Minor
- See all 30 studies
A decrease has been noted in persons without high cholesterol in the first place, and the decreasing effect of statins appears to be augmented with fish oil. However, in persons at higher risk for cardiovascular disease due to high triglycerides and cholesterol (who more frequently use fish oil as therapy) it is possible LDL-C may actually be increased. The magnitude tends to be in the 5-10% range.
grade-a - High See all 19 studies
No significant alterations in fasting glucose are seen over time with fish oil supplementation
grade-a - Very High See all 16 studies
Although some decreases have been noted, the vast majority of the evidence suggests that there is no significant influence
grade-a - Moderate See all 10 studies
Although the majority of evidence suggests absolutely no influence on HbA1c, reductions have been reported and a lone case has noted a clinically irrelevant increase of HbA1c (secondary to the increase in glucose). Practically, there is unlikely to be any large changes
grade-a - Very High See all 12 studies
No significant influence on insulin sensitivity seems to be the consensus, although there are isolated reports of both an increase and decrease (in response to a glucose tolerance test and fasting, respectively)
grade-a - Very High See all 18 studies
Although some decreases have been noted, overall there does not appear to be a significant clinical reduction in total cholesterol like there is with triglycerides
grade-a - High See all 14 studies
For the most part, no significant influence on body weight over time
grade-b Notable Very High See all 7 studies
The decrease in symptoms of lupus as assessed by SLAM-R and BILAG at times reaches up to 50% symptom reduction and tends to exceed 30%, and the first pilot studies noted remission in all subjects (although they have not been replicated since). Oddly, benefit may come from lower doses (160mg EPA and 140mg DHA) with higher doses conferring less benefit
grade-b
Minor
Low See all 8 studies
Appears to be able to reduce cellular adhesion factors (that draw immune cells into tissue to aid in inflammatory processes, reducing these is immunosuppressive) in elderly persons, while slightly increasing expression in youth
grade-b Minor Low See all 4 studies
A possible reducing effect of fish oil supplementation on cortisol
grade-b Minor Very High See all 4 studies
There appears to be a slight increase in vascular reactivity and blood vessel responsiveness that may be independent of both blood flow alterations and blood pressure
grade-b Minor Very High See 2 studies
There appears to be an increased infant birth weight in mothers that consume fish oil (or fish weekly) relative to no fish oil intake. Although earlier studies have suggested this may due to prolonging pregnancy, a recent RCT found an increase in birth weight independent of gestational age.
grade-b
Minor
- See all 5 studies
Both increases and decreases in lipid peroxidation have been noted with fish oil supplementation, with the increases in peroxidation usually seen with high doses of fish oil paired with other oxidative stressors (such as marathon running)
grade-b Minor High See all 3 studies
Although there do not appear to be changes in the amounts of NK cells in the body following fish oil, their activity appears to be a tad reduced
grade-b Minor Very High See all 3 studies
There appears to be reduced risk of DNA damage, immunosuppression, and erythema in response to sunlight associated with fish oil consumption. Studies have only investigated higher doses (1,800mg EPA minimum) and it is unsure if these protective effects apply to lower doses
grade-b Minor High See all 4 studies
Possible decreases in platelet aggregation
grade-b Minor Very High See all 5 studies
There appears to be reduced depressive symptoms in bipolar disorder when the depression is of a large magnitude (similar to the anti-depressant effects of fish oil in general). There may not be a reduction in depressive symptoms with lower severity depression (a trend to increase has been noted) and manic symptoms do not appear to be significantly influenced.
grade-b Minor High See all 6 studies
May decrease TNF-a
grade-b Minor Very High See all 6 studies
May decrease vLDL cholesterol
grade-b - Moderate See all 6 studies
Although at least one study has noted a decrease, usually there is no significant changes
grade-b - Very High See all 3 studies
The overall quantity of B lymphocytes does not appear to be altered with fish oil supplementation
grade-b - Moderate See all 5 studies
Although there is some counter evidence to suggest an improvement of small magnitude, most evidence suggest no significant changes in blood flow
grade-b - Very High See all 10 studies
No significant influence on fasting insulin levels
grade-b - Very High See all 5 studies
There does not appear to be an augmented insulin release from dietary carbohydrate nor an inherent insulin release from the pancreas associated with fish oil supplementation
grade-b - High See all 3 studies
Although one study suggests a decrease, most evidence suggest no significant influence
grade-b - High See all 3 studies
Although one increase in NK cell content has been noted after exercise, the two studies using similar doses at rest have failed to find a significant influence on NK cell content
grade-b - Very High See all 5 studies
There does not appear to be any unique effect of supplemental fish oil on postpartum depression. Fish oil in postpartum and perinatal periods follows the same motifs as other depressive states, with EPA being the active molecule but likely only of benefit in major depressive disorder
grade-b - Very High See 2 studies
There does not appear to be a significant protective effect against pre-eclampsia in women who supplement fish oil during pregnancy
grade-b - High See all 4 studies
Although there is some evidence to suggest an immunosuppressive effect on T cells, most evidence suggest no significant effect. When the immunosuppresion does occur, it is due to the EPA content
grade-b - Very High See all 3 studies
There is no evidence to support an improvement of VO2 max when fish oil is consumed alongside an exercise routine
grade-c Notable - See study
5-HEPE is a catabolite of EPA, and its blood levels are increased following consumption of EPA in a dose-dependent manner
grade-c Minor - See study
A decrease in aggression has been noted, which is thought to be secondary to improvements in mood state and general well being
grade-c Minor Very High See 2 studies
A decrease in anxiety has been noted in medical students
grade-c Minor - See study
Appears to improve cerebral blood flow and volume in persons with low dietary fish intake
grade-c Minor - See study
The increase in cerebral oxygenation appears to exist in otherwise healthy persons with low dietary fish intake, and appears to be secondary to improvements in blood flow in general
grade-c Minor Very High See 2 studies
High dose (900 mg) DHA appears to be somewhat beneficial in reducing the rate of cognitive decline in elderly but otherwise healthy persons, but 350 mg DHA and 600 mg EPA has been seen to have no effect in those with concurrent age-related macular degeneration.
grade-c Minor Very High See 2 studies
Ingestion of fish oil appears to prolong the time required for sunlight to induce reddening of the skin, and secondary to this fish oil ingestion above 1,800mg EPA is able to reduce the risk of sunburn.
grade-c Minor - See study
Exercise induced oxidation has been noted to be increased in elite athletes with fish oil supplementation
grade-c Minor - See study
An increase in serum Factor VII has been noted with fish oil supplementation
grade-c Minor Moderate See 2 studies
May increase general oxidation in the body, but seems unreliable in doing so
grade-c Minor Very High See 2 studies
May decrease homocysteine content
grade-c Minor - See study
A reduced risk of death of infants after pregnancy has been noted with maternal consumption of fish oil, but this information is preliminary and needs replication (noted offhand in one study)
grade-c Minor Moderate See 2 studies
Mixed effects on IL-2 concentrations, with an increase noted when supplemented around exercise and no change noted at rest.
grade-c Minor - See study
A decrease in circulating IL-6 has been noted with fish oil supplementation
grade-c Minor - See study
An increase in ketone bodies has been noted when fish oil is paired with a weight loss diet (relative to placebo)
grade-c Minor Very High See 2 studies
An increase in LKB5 has been noted following fish oil supplementation
grade-c Minor - See study
A possible decreasing effect of liver fat seen in persons with NAFLD
grade-c Minor - See study
A decrease in lymphocytic count has been noted in obese persons
grade-c Minor - See 2 studies
Possible improvements in memory
grade-c Minor - See study
An increase in exercise-induced nitric oxide production has been noted
grade-c Minor - See study
An increase in PAI-1 is noted with fish oil supplementation
grade-c Minor - See study
An improvement in processing accuracy (assessed by amount of errors in a cognitive test) has been noted with fish oil in otherwise healthy adults that do not frequently consume fish products
grade-c Minor - See study
An increase in prostaglandin J2A is noted with fish oil supplementation, which is thought to mediate a variety of fish oil's effects
grade-c Minor - See study
A reduction in reaction time has been noted with fish oil supplementation in persons who consume low levels of fish in the diet
grade-c Minor - See study
Self-reported stress in distressed women given fish oil supplementation appears to be reduced
grade-c Minor Moderate See all 3 studies
An improvement in well being has been noted in nondepressed and nonelderly obese persons given fish oil supplementation to a small magnitude.
grade-c Minor - See study
An increase in thromboxane B2 is noted with fish oil supplementation
grade-c - - See study
5-HETE is a catabolite of arachidonic acid (omega-6 fatty acids), and its serum levels do not appear to be significantly influenced by ingestion of fish oil supplementation despite an increase in EPA and DHA
grade-c - Moderate See 2 studies
No significant influence on Adiponectin concentrations
grade-c - Very High See 2 studies
No significant influence on Apolipoprotein A concentrations
grade-c - Very High See 2 studies
Fish oil supplementation in otherwise healthy adults has failed to significantly influence attention processing
grade-c - - See study
Despite the importance of DHA in cognition of offspring (and absolute deprivation likely to reduce cognitive development), additional supplemental fish oil does not appear to be supported for further enhancing the cognition of offspring although it is plausible
grade-c - - See study
No significant influence on DHEA sulfate in serum
grade-c - Very High See 2 studies
Does not appear to influence DNA damage
grade-c - - See study
Does not appear to augment nor alleviate the immunosuppression that occurs during exercise in otherwise healthy persons
grade-c - Very High See all 3 studies
No significant influence on fat mass with routine supplemental fish oil
grade-c - Moderate See 2 studies
No demonstrable benefit to fatigue
grade-c - Very High See 2 studies
There does not appear to be a significant influence of fish oil supplementation on food intake
grade-c - - See study
No evidence to support an increase in fructosamine, which alongside HbA1c is thought to indicate pathology from elevated blood glucose (fish oil appears to elevate glucose, but does not appear to be associated with higher diabetes risk)
grade-c - - See study
No significant influence on plasma glucagon concentrations
grade-c - - See study
No significant acute effect on heart rate seen with fish oil supplementation
grade-c - - See study
No significant influence on circulating IL-1β concentrations
grade-c - - See study
No significant influence on circulating IL-5 concentrations
grade-c - Very High See all 3 studies
No significant influence on lean mass associated with fish oil supplementation
grade-c - Very High See 2 studies
No significant influence on Leptin in serum
grade-c - Very High See 2 studies
No significant influence on LKB4 concentrations
grade-c - - See study
No significant influence on liver enzymes noted
grade-c - - See study
No significant influence on biomarkers of muscle damage seen with fish oil supplementation
grade-c - Very High See 2 studies
No significant influence detected
grade-c - - See study
Although a trend to reduce protein losses in the urine was noted (which would be kidney protective), this was a statistically insignificant and secondary to lupus treatment
grade-c - - See study
No significant influence on SHBG levels
grade-c - - See study
Despite the benefit seen with high dose DHA in cognitive decline, there does not appear to be a proven significant protective effect in persons already with Alzheimer's
grade-c - - See study
No detectable influence on testosterone levels in serum
grade-d Minor - See study
An increase in fat oxidation (percentage of energy being taken from fat tissue) has been noted with fish oil supplementation
grade-d Minor - See study
Effect occurs in normal-weight women, but not obese women.
grade-d - - See study
No significant influence on bone mineral density noted with fish oil supplementation
grade-d - - See study
No significant influence on metabolic rate seen with fish oil supplementation
grade-d - - See study

Studies Excluded from Consideration

  • Confounded with other fatty acids[1]

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