Note: This article was originally published in June 2015 and was updated in January 2017 to include the latest research. My original recommendations still stand, and the case for high-dose fish oil supplementation has become even weaker.
Fish oil supplements continue to gain in popularity, but the research supporting their efficacy is shaky.
For over a decade, fish oil has been touted by doctors, nutritionists, and armchair health enthusiasts alike as a near cure-all for health. Whether you have heart disease, depression, diabetes, or joint or skin problems, or you just want to stay healthy and prevent nutrient deficiencies, somebody has probably told you to take a fish oil supplement.
The general notion was that it might help, and at the very least, it couldn’t hurt. Unfortunately, that isn’t necessarily the case.
Does Fish Oil Really Prevent Heart Disease?
But a majority of the evidence available now suggests that fish oil provides no benefits for preventing or improving heart disease.
For example, two randomized controlled trials (RCTs) published in 2010 found that in adults with preexisting heart disease, long-term supplementation (three-plus years) with fish oil had no significant impact on cardiovascular end points. (2, 3)
A few other trials looked at the effect of short-term fish oil supplementation on atrial fibrillation, and none of them found that fish oil improved patient outcomes. (4, 5, 6)
A meta-analysis of RCTs in 2012, focusing on cardiovascular end-points, found that fish oil did not reduce cardiovascular events or death and concluded that the evidence does not support using fish oil supplements for the secondary prevention of heart disease. (7)
Three other meta-analyses published since then came to similar conclusions. (8, 9, 10)
Some studies do still come up with positive results. For example, one meta-analysis published in 2013 found a protective effect of fish oil for preventing cardiac death, sudden death, and myocardial infarction. (11)
Is it possible that fish oil is beneficial for one person and harmful for another? #fishoil
But there are also studies with negative results. Back in 2010, I wrote an article highlighting one study where long-term fish oil supplementation resulted in an increase in heart disease and sudden death and another that found increased LDL levels and insulin resistance in people who took 3g per day of fish oil. (12, 13)
Overall, the majority of studies show neither benefit nor harm from supplementing with fish oil for heart disease.
Does Fish Oil Improve Metabolic Syndrome?
Metabolic syndrome is a collection of symptoms and biomarkers that often precedes heart disease or diabetes.
On the positive side, a recently published RCT found that in adults with metabolic syndrome, supplementation with 3g/d of fish oil along with 10 mL/d of olive oil for 90 days improved several blood markers. This includes a statistically significant lowering of triglycerides and LDL cholesterol, an improvement in LDL/HDL ratio, and improved markers of oxidative stress. (14)
It’s interesting to note that the fish oil plus olive oil group had better results than either the fish oil or olive oil group alone. One possible reason for this is that olive oil is rich in antioxidants and may have protected against the potentially greater risk of oxidative damage from consuming more polyunsaturated fat.
On the negative side, a recent study in women with metabolic syndrome found that 3g/d of fish oil resulted in an increase in LDL cholesterol, blood glucose, and markers for insulin resistance after 90 days, although they did observe a decrease in blood pressure. (15)
And in overweight men, supplementation with 5g per day of krill and salmon oil resulted in increased insulin resistance after eight weeks, compared with a canola oil control. (16)
Finally, an impressively large RCT involving over 12,500 patients with diabetes, elevated fasting glucose, or impaired glucose tolerance found that supplementation with 1g/d of omega-3s for six years did not reduce disease endpoints compared to placebo. Endpoints measured included incidence of cardiovascular events, death from cardiovascular events, and death from all causes. (17)
Can Fish Oil Prevent Cancer? Or Does Fish Oil Cause Cancer?
Many of you probably recall headlines from 2013 proclaiming that fish oil may increase the risk of prostate cancer (18). But despite the extensive media attention garnered by the study, it’s actually one of the weaker cases that have been brought against fish oil.
Believe it or not, the study in question actually had nothing to do with fish oil, or even omega-3 supplements. The researchers simply measured circulating levels of omega-3 fatty acids in men with and without prostate cancer and found that men with prostate cancer tended to have higher concentrations of omega-3s in their blood.
There are several reasons this could be the case; for instance, some evidence indicates that having prostate cancer might itself increase blood levels of omega-3s, or that certain genetic polymorphisms can increase both circulating omega-3s and cancer risk.
It didn’t take long for other researchers to publish a slew of comments pointing out these possibilities, but the media had already taken the “fish oil causes cancer” stance and run with it.
More recently, a meta-analysis found that in general, omega-3 consumption is associated with a decreased risk of prostate cancer, but that the correlation is too weak to be statistically significant. (19) In 2016, a massive meta-analysis looked at 44 studies and concluded overall that higher omega-3 supplementation had no effect on prostate cancer mortality (20).
A handful of reviews found that fish oil intake was associated with a lower risk of breast cancer, although no distinction was made between fish oil supplements and fish consumption. (21, 22) And one RCT published in 2012 found that supplementation with 600mg of omega-3s per day had no effect on cancer risk in men, but increased cancer risk in women. (23)
As with heart disease and metabolic syndrome, the research on omega-3 and fish oil supplementation on cancer is decidedly mixed.
High Levels of Oxidative Products Found in Fish Oil Supplements
Recently, attention has been drawn to the quality of over-the-counter fish oil supplements. Long-chain polyunsaturated fatty acids, including DHA and EPA, are especially susceptible to oxidation due to double carbon bonds at multiple locations. Light, oxygen exposure, and heat can all contribute to oxidation. Oxidized lipids have been linked to a number of health issues, including organ toxicity and accelerated atherosclerosis—the exact opposite outcomes usually desired by those who supplement with fish oil. (24)
In 2016, the top three selling fish oil supplements in the United States were shown to have oxidation levels up to four times higher than recommended “safe” levels. (25) One caveat of this alarming study is that oxidation levels were normalized per 1g of omega-3s in the supplements, instead of the industry standard of normalizing per 1g of fish oil. Although this does inflate their three measures of oxidation, all three fish oil brands were still above acceptable levels of peroxidase and TOTOX levels, while one (instead of the study’s reported two) was above acceptable anisidine levels if instead normalized per 1g of fish oil.
As oxidation level measurements of omega-3 supplements have increased over the last several years, this has been the common finding. Studies examining fish oil supplements available around the world, including in Canada, New Zealand, and South Africa, consistently show that a vast majority (up to 80 percent!) exceed at least one of the measures of acceptable oxidation levels. (26, 24, 27) Also noteworthy is that most of these supplements contain lower levels of DHA and EPA than the labels claim, probably partly due to oxidation.
Furthermore, the most recent study from 2016 demonstrated that over-the-counter omega-3 supplements had a decreased ability to inhibit small, dense LDL oxidation in a laboratory setting compared to pure omega-3 fatty acids. (25) This means that whatever supposed benefits omega-3 supplements should have on blood lipids could likely be completely counteracted by the oxidized lipids also contained in the pills. Overall, I am quite wary of most over-the-counter products out there.
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Should You Take Fish Oil?
To avoid making this article so long that nobody will read it, I haven’t included research on fish oil and other aspects of health, including mental health, skin health, pregnancy, and cognitive function. As you might imagine, the research on fish oil supplementation to prevent or improve these conditions is also somewhat mixed, with some studies showing significant benefit and others showing no change.
This is certainly an important topic, and I’m glad to see such a strong interest in it in the research community. I will continue to follow the literature and update my recommendations if and when new evidence comes to light, but for the time being this is what I would suggest:
If you are generally healthy, the best strategy is to consume about 12 to 16 ounces of cold-water fatty fish or shellfish each week. When possible, whole foods are always my first recommendation. Most studies show an inverse relationship between fish consumption and heart disease and mortality, so while fish oil may not protect you, eating fish does seem to. Perhaps this is because fish and shellfish contain many other beneficial nutrients that fish oil does not, including selenium, zinc, iron, and highly absorbable protein. (Fortunately, most cold-water fatty fish and shellfish are also low in mercury and other toxins, and mercury in fish may not be as big a problem as some have led us to believe.)
If you don’t eat fish (for whatever reason), I’d suggest supplementing with 1 teaspoon of high-vitamin cod liver oil. In addition to about 1.2 g of EPA + DHA, it is rich in the active forms of vitamin A and vitamin D, both of which are difficult to obtain elsewhere in the diet. There are very few studies suggesting the possibility of harm from supplementation with 1 gram or less of fish oil per day, and so I think one teaspoon of cod liver oil a day is likely to be safe even for those eating fish regularly—and beneficial for those not eating liver or other foods that contain active vitamin A. My current favorite cod liver oil is Rosita Extra Virgin Cod Liver Oil, as this company has consistently demonstrated very low levels of oxidative products from independent laboratory testing.
Based on the evidence I’ve reviewed in this article, I would not recommend consuming high doses of fish oil (i.e., more than 3g/day) over the long term. If you do choose to take a higher dose of fish oil, I would make sure to consume plenty of antioxidant-rich foods, like olive oil; blueberries; nuts; dark, leafy greens; and dark chocolate.
I think we still have a lot to learn about this subject. One of the challenges is that the effects of polyunsaturated fats on overall physiology are complex and probably depend on multiple factors that can vary individually, including uncontrolled oxidation, eicosanoid production, cell membrane effects, and signal transduction via specialized fatty acid receptors (i.e., PPAR receptors).
This could explain why we see such a wide variation in study results. Is it possible that 3g/d of fish oil is beneficial for one person and harmful for another? Absolutely. Unfortunately, at this point it’s difficult to predict that individual response with accuracy and certainty, so I think the conservative approach I suggested above is probably the most sensible until we learn more.
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In 2010 (when I was in my mid 30s) I started taking a reputable fish oil supplement as prescribed by a naturopath. At the end of the year I started getting lots of strong heart palpitations. I was given a Holter monitor to wear for 24 hours to record my heart beat. In the 24 hour period I had 285 extra beats and I was diagnosed with Ectopic beats. My heart palpations continued for at least a month. I stopped taking fish oil incase that was affecting me and my heart palpations went away. I have the odd palpations since then but nothing like during the time I was taking fish oil. I have not taken fish oil since this time.
Hi Chris! I had to stop taking fish oil because I was getting (grain of salt sized) cysts on my face. They were very hard & painful & would come to the surface of the skin. Since I have stopped taking the fish oil, I have stopped getting the cysts. I was taking a supposedly pure form from my Dr.’s office. Maybe it happened because I am histamine sensitive or maybe immpurities in it. Thanks for all your posts!
What about flax seed oil? Probably a paleo-no-go, but any comments about that oil?
The conversion of ALA to EPA and DHA is extremely limited. Less than 5% of ALA gets converted to EPA, and less than 0.5% (one-half of one percent) of ALA is converted to DHA. Therefore, flaxseed oil and other vegan sources of omega-3 EFAs are not an effective or economical way to get the intended benefit.
This is why it’s so difficult to interpret results like these. For the NEJM article “n–3 Fatty Acids and Cardiovascular Outcomes in Patients with Dysglycemia”, they used 1 gram/day of ethyl esters, and not “real” fish oil. First, they used a small amount per day. Second:
“A comprehensive review of the scientific literature does indeed provide evidence suggesting that fish oil in triglyceride form is more efficiently absorbed than fish oil in ethyl ester form [7, 8, 14-16].”
https://www.ascentahealth.com/omega-3-and-you/the-science/fish-oil-triglycerides-vs-ethyl-esters-comparative-review-metabolism-absorption-stability/
So, what does this mean for someone who tries to get their omega 3s from actual fish (usually sardines/anchovies), and who aims for 2-3 grams of omega 3 per day?
Probably not a lot, if anything.
I should note that the ethyl esters were from a drug manufacturer. It’s good to see a negative result from studies like this. (In the past, they used to hide negative results.)
I think that the HDL/LDL ratio is in someway misleading. It mostly depends on LDL particle number and oxidized cholesterol. It’s reliable just in some cases, that have been taken as a generalization. I perfectly agree with the article, most omega 3 oils are highly processed and lack of the food sinergy principle that sees food as a complex matrix of nutrients.
I think that Rosita cod liver food is indeed good since it uses a traditional method.
I really started thinking about taking fish oil since i suffer from eczema and dryness, also cant find good quality meat and eggs all the time, i also thought about taking hemp oil, i ahy away from cod liver since it has a high vitamin a level.. what are your thoughts ?
Hi Chris
You should go through the studies and discard all those where they did not measure the oxidation levels of the omega3 oil and where they did not track it throughout the study. I am convinced that the contradiction in results are due to oxidation of the oils used during the study. How was it supplied to the participants? How did the participants store it? You correctly pointed out that omega3 is highly susceptible to oxidation and strong light, UV (even from lights) and high temperatures will accelerate oxidation.
It will be quite interesting to see whether there is a better correlation between results from different researchers after the others have been discarded.
I found your article very interesting. My experience with fish oil is that it ‘seems to’ increase my blood sugar readings. I find I can’t take it for another reason, and that is that my gall bladder definitely does not like it! It can precipitate a gall bladder attack.
My naturopath who uses muscle testing, tested me for a number of different brands of fish oil, plus krill oil, and found that none of them were good for me, which confirms my own practical results. I have to be very cautious even with eating things like sardines, etc. (plus olive oil.) I do use chia seed, which I’m hoping will provide some Omega 3. I will not use flaxseed, which is still touted as being very healthy, but I believe it is toxic.
I’ve always felt bad that I can’t seem to tolerate fish oil, which my doctor tells me I should have, and this article seems to indicate that there is or can be a down-side. I’d like to see an article on sources of Omega 3 that the fish themselves feed on, as there seems to be some confusion about this.
What about cod liver oil supplementation for toddlers? Is it necessary?
Do you consider krill oil in the same category?
My dog is on it for osteosarcoma. Any research on that?
Some caveats regarding this fish oil article:
The authors never name the three supplements they tested. Good scientific research depends upon replication by other scientists; yet concealing the brands that were tested eliminates the possibility of other researchers examining the same products. Red flag one.
In one section of the article, the authors refer to the tested supplements as “three widely used DS”. In other sections, they refer to the tested supplement as “top selling DS”. Those references could mean the same thing, or not, but it is impossible to know without specifics. Red flag two.
When the authors refer to the tested supplements as “top selling DS”, not source of the data used to determine the ranking of dietary supplement fish oil is ever presented. Red flag three.
The authors state the studies were conducted without any grant from any outside source, but the “medical writing assistance” was provided by Peloton Advantage (a PR company) and funded by Amarin Pharma, Inc (a manufacturer of pharmaceutical fish oil). Of course this had no influence on the findings that pharmaceutical fish oil is much preferred over the dietary supplement fish oil. Surprise, surprise. Which brings to question, if there was no outside funding for the research, but only the writing, why was the research done in the first place? Elucida research (for which the authors work) is a contract research facility. Massive red flag.
Should have mentioned — the article to which I refer above is number 25 in the references.
I have not been able to tolerate even the smallest dose of fish oil since becoming chronically ill 7 years ago. I tried repeatedly and it always made me so sick with nausea, headaches and liver/gall bladder pain. I only recently discovered why. I am amine intolerant, a legacy of mercury toxicity from amalgams. Fish oil is very rich in amines.
Interesting…amines
I am currently taking fish oil supplements upon the recommendation of my doctor and am not planning on stopping at this point based on what you have in this article. Here is my reasoning:
I was diagnosed with T2D about 17 months ago despite not being overweight or having any of the normal characteristics.
After much frustration with both my PCP and Endocrinologist, I fired them and got a new doctor who tested me for everything under the sun. In short, not only am I not insulin resistant, I actually process carbohydrates better than average. However, I was deficient or borderline in all the B vitamins except B1 as well as in iodine and borderline on magnesium and my Omega 3 to Omega 6 ratio was way out of whack.
I have been continuing to track my BG readings (AM fasting, 2 hrs after every meal and post workout) for the 7 weeks since beginning the supplementation B vitamin complex, iodine and Omega 3 (via fish oil). The results, which I track on an Excel spreadsheet, clearly show a solid down trend in all readings.
I plan on continuing my current course of action until all of the trend lines level out for a 30 day period. At which time, if they are NOT in an acceptable range, I will look at making other changes. If they are in acceptable ranges, I would expect my A1c to also be acceptable again. If this is the case, I may stop taking the fish oil as an N=1 experiment to see if there is any impact – positive or negative. However, given my current supplementation regimen seems to be producing very good results to point of an average of 15.5 pt drop per category in just 7 weeks, I think it unwise to change anything I am doing right now.
That said, I also understand I changed multiple things all at once and can therefore not attribute results to any one thing and know that this one item might not be having any effect which is why I am open to the N=1 experimentation down the road.
Cliff – you may not have Type 2, but a Type of monogenic diabetes that may be being overlooked.
Who is your doctor?
Hard end points are “hard” to find. From my personal experience, I can say that that the long chin fatty acids in fish oils, sardines and salmon (I eat 2 servings of each, each week) plus supplementation suppressed my immune system and proved their anti-inflammatory biochemistry. Of course, I reduced my intake of supplements. The 2 supplements I use and recommend come with antioxidants (the olive oil the other vitamin E). Also, I recommend taking the fish oil with one’s multi vitamin and other antioxidant supplements. I think we can show evidence for lowering triglycerides with EPE/DHA.
been taking pharmaceutical grade fish oil, 3 grams a day for several years. it has dramatically reduced my triglycerides and LDL. I take the DHA dominant formula.
Good point Paul – ratios of DHA to EPA are reversed in fish oils compared to fish
Interesting. I’ve been taking high quality DHA-dominant fish oil supplements for at least three years. My triglycerides have always been good, but total cholesterol and LDLs are still high. Am addressing hypothyroidism now, and I read that this can be a reason for my LDLs and total cholesterol being high. Also, Type A bloodtypes typically have weak gallbladder and difficulty digesting fats, so I sometimes wonder how my body is handling the fish oils.
Would krill oil be included in these studies of fish oil?
I’d like to know about krill oil too.
Natural fish oil is effective at reducing Inflammation if you take about 2 grams of Omega-3 each day and REDUCE your intake of Omega-6
It is not effective if you only take 1 tiny capsule a day. You have to take at least 2 grams
I have a friend who had severe pains in his knee joints and his doctors had suggested surgery
I suggested a double dose of 4 grams a day of Omega-3 for 3 months and then reduce to 2 grams a day
Within 1 month he called me and told me that his pain had gone and surgery was no longer necessary. That was 2 years ago and he is a much happier person
It works for most Inflammation, such as early stage Rheumatoid Arthritis, Asthma and especially early stage Endometriosis.
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Hi Chris,
What’s your opinion regarding Green Pasture Fermented Cod Liver Oil and High Vitamin Butter oil?
Yes!!! I was going to ask the same thing!
I think a better way to go is to consume cod livers themselves, which you can purchase canned (Amazon has them). The cost is more economical than buying the top-rated cod liver oils like Rosalita, and you are getting a whole food product. I just keep the can in the refrig or freezer and take a spoonful with lunch, or whatever meal is most convenient for you. Taste is not bad….just a very mild fishy taste.
wow, thanks for this info!
This is very good info. How do they taste?
The taste of the canned cod liver oil is fine…….kind of a buttery texture, with a very mild fishy taste – not unpleasant at all. Some people spread it on toast, I guess, but I don’t eat bread, so I just take a spoonful of it with my daily lunch or dinner.
Great idea !! Thank you Rob !!
Hello my name is Renee and I’m 62. I’ve been taking cod liver oil for a few weeks now. Currently I’m suffering from a resurgence of severe ME/CFS. I’ve had to move in with my parents and have had to go on disability. I’m so ill, and my brain is floating and foggy and its hard to type this or read much or just stay upward. So I’m taking this for my brain and now I’m stopping after reading this article. So many body systems are affected by this and they know so very little that I’m afraid to put what may help/not help into my system. Thank you very much for your research Chris. I follow you regarding digestive issues which are a part of this disease. I know one sure thing though Thank God for probiotics! You set me on a good path there! You are helpful and I’ve nowhere else to go. Thank you for your knowledge
Renee,
Having had my share of debilitating health issues such as Lyme, and pharmaceutical injuries from CIPRO…
I have found a few significant things that have made a difference.
Magnesium Oil Spray – Ancient Minerals
Vitamin D3 – Thorne Research
Phosphatidylserine & Phosphatidylcholine
Trans-dermal Magnesium has been and remains an enormous blessing… and fast working. Applying liberally and then wiping off with warm wash cloth daily has eased so many aches, as well as brought mental calm and even energy. Simply a vital mineral for all, especially those with chronic health conditions that are autoimmune. The Transdermal application allows for a very effective delivery of ” intracellular’ magnesium. This is exactly where you need and want it. Starving for magnesium leads to a host of issues that are vast and far reaching. Oral supplementation cannot answer the needs well enough to address the depletion.
The Phosphatidylserine & Phosphatidylcholine are super super important to the membrane of the cells for the necessary communication signalling and absorption of nutrients as well as detoxification of the cells.
Vitamin D levels should be up to 80 for optimal health levels. Not the dismal 50 or below.
Get tested if havent already.
God Bless
Thank you I will do these things. Thanks for the reply
Renee,
I have struggled with CFS for 20+ years and have researched many supplements. I have found the following to be helpful for me:
Magnesium Malate (Mg & Malic Acid) Source Naturals – muscle spasms & aches 3x day
Low Dose Naltrexone (instant release-compounded Rx from Belmar Pharmacy in CO) – pain relief 1x day
Butterbur w/ Feverfew – NOW Foods – improves tolerance of neurological disturbances ( light, sound, temp, migraines)
I hope these suggestions might help. Adopting a gluten-free, dairy-free, low sugar lifestyle has also impacted pain and energy levels.
Best of luck!