Modern Western diets are dramatically low in anti-inflammatory omega-3 fats, which contributes to heart disease, cancer, and other chronic conditions. Fish oil is an excellent source of omega-3s that can reduce inflammation and protect the heart, brain, bones, and more. Read on to learn the benefits, dosage, and safety of fish oil supplementation.
What is Fish Oil?
Fish oil is a great source of anti-inflammatory, omega-3 healthy fats. It contains two omega-3 fatty acids known as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Our bodies can produce them from an essential fatty acid, ALA, but the efficacy of this conversion is questionable [1, 2].
The ideal omega-3/omega-6 ratio in the body is 1:1 – 1:3, which is associated with a lower lipid count, healthier blood vessels, and reduced risk of chronic conditions .
DHA is highly concentrated in the brain, retina, testicles, and semen.
- Essential for brain and heart health
- Reduces blood triglycerides
- Potent anti-inflammatory effects
- Supports mental health
- Improves skin health and appearance
- Protects the bones and joints
- Supports pregnancy and fetal development
- Quickly goes rancid
- Doesn’t lower blood sugar
- May not help with eczema
- Might interact with blood thinners
- May cause fishy burps and nausea
Dietary omega-3 fatty acids have potent anti-inflammatory effects, and they may be beneficial for a range of inflammatory conditions .
In one study, men who took DHA supplements for 6-12 weeks decreased the concentrations of several inflammatory markers in their blood by approximately 20% .
In a study of 174 Alzheimer’s disease patients, fish oil higher in EPA than DHA lowered inflammatory cytokines, such as IL-6 and IL-1β, associated with neurodegenerative and autoimmune diseases .
EPA and DHA produce molecules known as “resolvins”, which are named for their ability to “resolve” inflammation. DHA also produces NPD1 molecules, which have anti-inflammatory properties in the brain [7, 8].
Studies show that dietary supplementation with fish oil lowers the activity of chronic inflammatory and autoimmune diseases including rheumatoid arthritis, Crohn’s disease, ulcerative colitis, psoriasis, lupus erythematosus, multiple sclerosis, and more [9, 10].
1) High Triglycerides
Both EPA and DHA have the ability to reduce triglyceride levels, most effectively after several weeks of supplementation.Reduction levels range from 15% up to 50%, and their effect is backed up by plenty of well- designed clinical trials [11, 12, 13, 14].
Many of these studies also showed their ability to increase HDL cholesterol, but the results were less consistent.
Based on these results, the FDA has approved omega-3-based prescription drugs for high triglycerides (hypertrigliceridemia): Lovaza (formerly Omacor), Omtryg, Vascepa, and Epanova .
It is important to note that the above formulations have a much higher EPA/DHA content than fish oil supplements, and they contain specific forms (esters) of these fatty acids. Unlike nutritional supplements, they go through rigorous quality controls by the FDA [15, 16].
The American Heart Association recommends taking 4g/daily of prescription omega-3s for optimal effects on blood triglycerides. These amounts are hard to obtain from most commercially available supplements .
What’s more, DHA-containing products might increase LDL cholesterol, which is not an issue with some pure-EPA prescription omega-3s [18, 16].
2) High Blood Pressure
According to a comprehensive meta-analysis of 70 clinical trials, supplementation with omega-3s from fish oil (EPA + DHA) significantly reduces both systolic (by 2.5-5.5 mmHg) and diastolic (by 1.5-3.5 mmHg) blood pressure. The effects are more pronounced in people with moderate, untreated hypertension .
Both 1 g and 2 g of ethyl-EPA helped alleviate the symptoms of depression in 75 patients with bipolar disorder .
In a study of 60 depressed patients, EPA was equally effective in reducing the symptoms as an antidepressant drug fluoxetine .
Multiple clinical reviews and meta-analyses have found beneficial effects of fish oil/omega-3 supplementation on depression symptoms. Truth be told, the observed benefits were mild, and the researchers emphasized the low quality of the available evidence [22, 23, 24].
DHA significantly reduced aggression due to mental stress in a study of 41 students. The same group of authors failed to confirm this benefit in non-stressful situations [25, 26].
In a 6-month study on 200 schoolchildren aged 8-16 years old, omega-3 supplementation caused a significant reduction in several measures of aggression .
5) Rheumatoid Arthritis
Resolvins found in EPA and DHA appear to prevent certain inflammatory cytokines such as TNF-α from inducing pain .
A meta-analysis of 17 trials found that supplemental fish oil reduces inflammatory joint pain from rheumatoid arthritis and other inflammatory conditions .
Omega-3’s were as effective as ibuprofen in reducing pain caused by arthritis, according to a study of 250 patients .
One clinical review underlined the promising benefits of fish oil for rheumatoid arthritis patients and suggested further, well-designed trials to unlock its full potential .
6) Skin Protection
According to preliminary research, high intake of omega-3 fats is associated with lower rates of skin cancer. Omega-3s may protect the skin by preventing the temporary suppression of the immune system caused by sunlight [32, 33].
In 42 volunteers, EPA supplementation prevented UV skin damage as seen in skin cancer .
Fish oil decreases skin inflammation caused by UV light in another small trial .
7) Painful Periods
In three studies of 380 participants, fish oil, alone or in combination with vitamin B1 or vitamin E, reduced pain, NSAID use, and quality of life in adolescent girls and women with painful periods (dysmenorrhea) [36, 37, 38].
In a study of 81 young patients with mild psychosis, low-dose omega-3 supplementation (1.2 g/day) significantly reduced the incidence of psychotic disorders .
Further trials should investigate this potential benefit of omega-3/fish oil.
Observational studies suggest that higher intake of omega-3 and lower intake of omega-6 fatty acids correlate with improved bone mineral density (BMD) in older adults [40, 41].
In a small trial of 65 older women, a combination of EPA, GLA, and calcium significantly increased BMD .
However, a review of 10 studies concluded that the effects of omega-3s on bone health are mild and probably stem from concurrent use of calcium and other supplements .
Taking mega-doses (7.5-8.1 grams daily) of fish oil slightly slowed down weight loss in 67 patients with cancer-related cachexia (severe weakness and wasting) [44, 45].
Lower doses (3 grams daily) do not seem to have beneficial effects .
According to a meta-analysis of 10 trials involving 699 children, omega-3 supplementation showed a “small but significant effect in improving ADHD symptoms.” Supplements with a higher EPA content appear to be more effective .
That said, a review published in 2019 regarded the benefits of fish oil for ADHD as insignificant .
Further research is needed to evaluate the efficacy of omega-3 fatty acids for ADHD symptoms and determine the optimal dosage and formulation.
No valid clinical evidence supports the use of fish oil for any of the conditions in this section. Below is a summary of up-to-date animal studies, cell-based research, or low-quality clinical trials which should spark further investigation. However, you shouldn’t interpret them as supportive of any health benefit.
Fish oil improved blood flow to the brain in 22 healthy individuals .
According to observational trials, increased dietary intake of fish and fish oil is associated with lower stroke rates. Data from clinical trials are less convincing; they point to mild beneficial effects on thrombotic (blood-clotting) but not hemorrhagic (bleeding) stroke [50, 51].
The brain protection likely stems from omega-3 fats, especially DHA, which combat inflammation and shield the blood vessels from clotting .
In 66 patients with rheumatoid arthritis, high doses of fish oil decrease disease activity and a number of tender joints, even after they discontinued NSAID treatment (diclofenac) .
13) Heart Health
High triglyceride levels, a risk factor for various cardiovascular diseases, are effectively reduced by EPA and DHA from fish oil [11, 12, 13].
Normalizing the is linked to cardiovascular protection .
Studies show that higher intakes of DHA+EPA improves omega-6/omega-3 ratio, which is associated with improved heart health. A ratio of 4:1 and lower is associated with a significant reduction of heart disease rates and different inflammatory conditions [54, 55].
Scientists are warning that we evolved with a nearly 1:1 ratio, and this ratio in a modern western diet can reach up to 16:1 .
According to an older review of clinical evidence, fish oil supplementation is associated with a significant reduction in mortality from heart disease .
However, a recent comprehensive review from the Cochrane database—79 trials of over 112,000 total participants—found no significant benefits of omega-3/fish oil supplementation on heart disease and related mortality .
A study published this year included 25,871 participants and came to the same conclusion .
14) Weight Loss
Fish oil’s anti-inflammatory effects have the ability to indirectly aid in fat metabolism in people with high inflammation or metabolic syndrome .
It can increase the secretion of adiponectin, which is responsible for breaking down fats .
In a large meta-analysis of 21 clinical trials, fish oil in combination with lifestyle changes significantly reduced waste-to-hip ratio (WHR) but failed to improve weight loss .
Current evidence can’t recommend fish oil as a complementary approach to weight loss. Still, obese people may benefit from its ability to reduce abdominal fat, which is a strong risk factor for heart disease .
15) Fertility and Fetal Development
Data suggests that fish oil may contribute to reduced reproductive aging and extended reproductive lifespan. High doses of fish oil supplementation improved markers of female reproductive lifespan 12 in women of normal weight, but had no benefits for obese women [63, 64].
The fetus of a pregnant woman requires EPA and DHA for proper development. DHA plays a significant role in the neural development of a fetus. The fetus is dependent on the mother to provide DHA, either through supplementation or diet [65, 66].
Breast milk is a significant source of DHA. A higher concentration of DHA in breast milk is connected to a mother’s diet and supplementation .
There is limited evidence that fish oil may reduce the risk of premature birth .
However, clinical trials that examined the effects of fish oil supplementation on infant development and cognition were less convincing. In two trials of 250 pregnant women, fish oil caused only minor improvements in infants’ cognition and coordination [69, 70].
The second trials followed up the infants for 12 years and found no long-term cognitive benefits of maternal fish oil supplementation .
16) Kidney Disease
Omega-3 supplementation improved kidney function in 97 diabetes .
However, it had no beneficial effects in another trial of 36 patients with diabetic nephropathy (kidney disease). More research is needed to draw a conclusion .
17) Inflammatory Bowel Disease
The anti-inflammatory effects of omega-3 fats may assist in managing inflammatory bowel disease (IBD) and other gastrointestinal diseases causing inflammation, but the available evidence is weak .
In one study, 4.2 grams of fish oil daily for 8 months reduced the symptoms of active mild-to-moderate ulcerative colitis .
However, a review of three clinical trials and 138 ulcerative colitis patients found no significant benefits of fish oil supplementation. The authors suggested further trials with improved fish oil formulation (enteric-coated capsules) .
18) Athletic Performance
Fish oil lowered heart rate and oxygen demand during exercise without interfering with performance in a study of 16 well-trained cyclists .
In 40 young wrestlers, fish oil (1 gram daily for 12 weeks) improved lung function compared to placebo .
In a study on rats, fish oil reduced the oxygen consumption of muscles, which promoted resistance to muscle fatigue .
On the other hand, fish oil supplements improved heart function but did not improve performance or recovery in 25 football players .
19) Cancer Prevention
The evidence about the role of fish oil in cancer prevention is conflicting.
According to different observational studies, increased intake of supplemental or dietary fish oil, as well as higher omega-3 blood levels, are associated with a lower risk of several cancers including skin, oral, prostate, colorectal, ovarian, and breast cancers [33, 81, 82, 83, 84].
On the other hand, some observational research and one large clinical trial (25,871 participants) failed to confirm this connection [85, 86, 87].
Well-designed should investigate this further and identify the factors contributing to mixed results. At this point, there’s insufficient evidence to suggest fish oil for cancer prevention.
A recent meta-analysis of 10 clinical trials summarized the available research on fish oil/omega-3 and migraine headaches. According to the results, supplementation may not reduce frequency and severity of the attacks but may significantly reduce their duration (3.4 hours) .
21) Alzheimer’s Disease
Preliminary studies showed that a high intake of DHA was associated with a reduced risk of developing Alzheimer’s disease .
In two studies of 1,600 older participants, increased consumption of fish oil and dietary fish was associated with lower rates of Alzheimer’s .
Preclinical studies indicate that DHA improves memory and can slow the progression of Alzheimer’s disease in mice .
However, in a meta-analysis of three clinical trials and 630 Alzheimer’s patients, omega-3 supplementation didn’t improve cognitive function .
22) Epilepsy (Seizures)
In 57 patients with chronic epilepsy, omega-3 supplementation (1 g EPA + 0.7 g DHA) significantly reduced seizure frequency over the first 6 weeks, but the effect was not sustained .
In a more recent trial of 24 patients with drug-resistant epilepsy, low-dose fish oil (3 caps/day, 1080 mg EPA+DHA) reduced seizure frequency by 33.6%. Further research is warranted .
Supplementary omega-3 fatty acids improved topical treatment in 30 patients with psoriasis by improving skin rash, scaling, redness, and other symptoms .
In two studies of 103 patients, omega-3 injections rapidly and significantly improved skin health and psoriasis symptoms [96, 97].
However, oral fish oil was no better than corn oil or olive oil in reducing the symptoms of psoriasis in two clinical trials of over 150 patients [98, 99].
24) Irregular Heartbeat
In a large meta-analysis of 51 trials (3,000 participants), omega-3 supplementation “mildly but significantly reduced heart rate.” DHA appears to be more effective than EPA .
On the other hand, two large studies failed to show the benefits of fish oil on different types of irregular heartbeat in patients with inserted devices (implantable defibrillators) [101, 102].
More studies are needed to shed light on the conflicting effects of fish oil on irregular heartbeats.
Omega-3 fats are essential for brain functions and development. Higher levels of DHA are correlated with improved verbal fluency in older people and better performance in middle-aged adults [103, 104].
Fish oil and DHA supplements improved cognitive function it two smaller clinical trials with young adults [105, 106].
However, a Cochrane database review analyzed three large well-designed clinical trials of more than 3,500 older participants. The authors found no significant effects on cognitive decline in healthy elderly .
Two recent studies of over 700 older people came to the same conclusion [108, 109].
According to preliminary clinical evidence, fish oil supplementation may not help with:
- Atherosclerosis [110, 111]
- Atopic dermatitis (eczema) 
- Atrial fibrillation (irregular heartbeat) 
- Helicobacter pylori infection 
- Menopausal symptoms 
- Preeclampsia (high blood pressure during pregnancy) 
Fish oil supplementation can reduce triglycerides in diabetes patients, but multiple clinical trials found it ineffective for improving the markers of blood sugar control [117, 118, 119, 120].
Fish Oil Side Effects and Precautions
When taken in moderate amounts (up to 3 g daily), fish oil supplements are safe for a general population. They are likely safe for pregnant women and children, too, when used in doses suggested by a healthcare professional .
The FDA labeled dietary fish oil as GRAS (generally recognized as safe) .
Possible side effects are mild and include :
- “Fishy burps”
- Bad breath
Large amounts of fish oil from dietary sources are possibly unsafe, due to the risk of contamination with environmental toxins and heavy metals. Pregnant women may be particularly sensitive to this .
When choosing a fish oil product, make sure to go with a trusted brand that purifies the oil and tests for contaminants. Unlike dietary supplements, prescription fish oil/omega-3 go through rigorous quality and safety controls.
High DHA doses may increase LDL cholesterol. People with high cholesterol may want to choose EPA-only formulations [18, 16].
Supplement-drug interactions can be dangerous and, in rare cases, even life-threatening. Always consult your doctor before supplementing and let them know about all drugs and supplements you are using or considering.
Drugs for weight loss (Orlistat) and oral contraceptives may hinder the absorption and reduce the effectiveness of fish oil [124, 121].
On the other hand, fish oil may enhance the effects of blood-thinners and high blood pressure drugs [125, 19].
Caution and strict medical supervision are warranted before combining fish oil with the above groups of drugs.
Fish Oil Supplementation
The below doses may not apply to you personally. If your doctor suggests using fish oil, work with them to find the optimal dosage according to your health condition and other factors.
The recommended daily dosage of fish oil supplements is 1,000-3,000 mg, depending on the condition. Adults should get at least two servings of oily fish per week, which is equivalent to about 500mg of omega-3 fats. Maximal results occur after approximately three weeks of taking supplements .
Some people respond better to high doses of fish oil. Maximum effects on triglyceride levels may require 4 g of prescription omega-3s daily .