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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I am particularly interested in Chris’s opinion on Green Pastures FCLO. I have followed his advice closely and even used the Healthy Baby Code prior to getting pregnant and also as a guide to feeding my babies. He always highly recommended it, and in particular, Green Pastures brand. I haven’t until today known that his recommendation had changed. I’m concerned it is because of something negative about the product. Wish I’d known before I purchased my most recent truck load of it.
Fermented cod liver oil and butter oil isn’t so healthy because of its omega fatty acids, but for its vitamins. These being A and D3 from de cod liver oil and K2 from the butter oil. These three vitamins work synergetically to get calcium where you need it in your body. That means in your bones and teeth, instead of in your veins, joints and other soft tissues.
I’m right there with you. I just had a baby 4 months ago and take it regularly. I was under the impression that he highly recommended the Green Pastures Fermented Cod Liver Oil. Would be helpful to know if he doesn’t recommend that any more and if not, the reasons behind it. I recently added the High Vitamin Butter Oil and wonder if that isn’t recommended either.
I now recommend either the FCLO, or Rosita’s EVCLO, which I have started using more myself and with my patients. I really like the transparency around their manufacturing process and the nutrient/fatty acid content of the oil.
Why are you taking any fish oil at all? You just wrote a fine article about how there is very little evidence for taking supplements.
After reading article by Brian Peskin about parent essential oils, I stopped using Alaskan Salmon Oil. I have been taking PEOs for a couple of weeks – too early to tell.
http://oxygen4life.com/
Make sure you take enough, I advise 6 caps a day for most women for the first 2 weeks then follow label. Most notice a difference within 2 to 4 weeks.
Various fish oils can have wide ranges in the omega 2’s they contain, so look at dosages before you decide/
It’s not a fish oil but a balanced seed oil mixture recommended by the top functional medicine guys she is taking.
My question is: what form of fish oil are these studies relying on? Are they studying fish oil in ethyl ester form (which doesn’t occur in nature and is the majority of fish oil supplements) or the triglyceride form (which does occur in nature and is much more absorbable). I think we need to made that distinction. Does taking one kind over the other matter?
You are quite right, the 3 dimensional structure does make a difference to absorbability and to effect. There are few studies that ever make the distinction you are seeking.
Yes, I am wondering if quality is being considered in these studies. Are they sure the fish oils aren’t rancid? I didn’t know about the ester vs. triglyceride form, so that does seem like an important point to consider.
For me the take away is that having fish in the diet seems like the way to go.
It’s so frustrating when a particular food or nutrient is given a bad rap, but the researchers don’t distinguish between high-quality and low quality versions of it when drawing their conclusions. It really does make a difference and can effect health dramatically. I think this is the main point that should’ve been brought up in the article.
Chris: I find a short-term improvement in inflammation when i take fish oil. Hence, when I experience outward signs of inflammation, I take fish oil for a couple days until the inflammation goes away.
Can I add my comment here, seems really appropriate: I take cod liver oil to reduce joint stiffness. When I was younger I would sometimes forget to take it for a few days and get a bit achy…Then I would use the British brand Seven Seas which would get my flexibility back fastest.
I have been doing this for 25 years, I really do notice the difference. Current intake is 4 grams daily, some cheaper brands some Seven Seas mixed. Still dancing in late sixties….
re: As with heart disease and metabolic syndrome, the research on omega-3 and fish oil supplementation on cancer is decidedly mixed.
This should surprise no one who has been following medical news lately:
http://www.drugawareness.org/editor-of-lancet-medical-research-is-unreliable-at-best-or-completely-fraudulent/
Nutrition ‘science’ is probably even less reliable and more biased.
On the topic at hand, context matters hugely (what else were the subjects consuming), and as several readers have pointed out: oil sourcing, processing, quality and age are significant.
Where this leaves us is personal results, and for Chris, minding the clinical outcomes. Formal science simply cannot be trusted, except as a source of vague hints for things that might need to be considered.
One of Chris’ dissenting diet colleagues, a cardiac MD, is having great results arresting and reversing heart disease with generous dose quality n3 DHA & EPA – but, importantly, in the context of a grain-free low-inflammatory LCHF diet that attends to vitamins B12 & D, as well as gut biome and thyroid. Those with FH are actually advised to take more n3.
I read a book recently (at the recommendation of my cousin Dave) called “Zero to One” by Peter Thiel and Blake Masters. You might know Peter Thiel as one of the founders of Paypal. He has an interesting quote “we know more about the physics of faraway stars than we know about human nutrition”.
I’ve been taking green pastures fermented skate oil. What is your opinion on fermented oils?
The JELIS trial (Lancet 2007;369:1090) conducted in Japan with over 18,000 subjects with cholesterol levels greater than 6.5 mmol/L (250 mg/dl), used 1.8 g of EPA (not DHA because DHA raises LDL), on top of statins. There was a 19% reduction in major coronary events in the subjects on EPA compared to statins alone; in addition, there was more than a 50% reduction in cardiovascular events among a subset of patients with elevated triglycerides. What’s remarkable about this study is that the Japanese already consume a lot of fish and generally have the highest blood levels of omega 3 fatty acids to start with.
The inclusion of DHA at high doses in many of the studies cited may actually have reduced the potential benefit of the fish oil treatments.
Dr. Jeff, what you say is totally true. I’m still “in” for the importance of the ratio, though…
You’re right, it is important but sourcing should be first consideration then you can balance.
This is discouraging for me because I do part time health coaching and often suggest that, among other dietary/lifestyle changes, clients supplement with fish oil in order to help increase HDL. I generally work with clients who know zero about nutrition/exercise, the vast majority of whom don’t care. However, the blood numbers that I see are often alarming, and I would like to be able to tell these clients something helpful in the 5 minutes that I get to spend with them. If fish oil is on its way “out,” what would you suggest I advise clients whose HDL numbers are despairingly low?
If you go to my website and read my articles, there might be some pearls there. Don’t despair about HDL numbers, help overall nutrition and health and the numbers will take care of themselves. How you feel is the best indication of health.
Thank you!
I once transformed my buddy’s limping arthritic labrador with a dry itchy coat and a sad demeanor to an oily smooth itch free coat happy dog that had a spring in his step with one week of salmon oil. Thats all the randomized control studies that I need. Fuckin research, it can prove whatever you want it to prove. Epidemiology and Empirical science is where it is at.
Nice article, thanks. I took fish oil capsules for years and found it helped mood, skin moisture. Menopause changed all of that. Fish oil seemed to cause heart palpitations. Even after adjusting for the onset of hypothyroidism with t3/t4 combination, fish oil would send the old ticker into wheelies! Just about that time, some of the referenced studies came out and I haven’t taken it since. No problems eating moderate amounts of fish per week.
I’ve taken high quality fish oil for years because it thins the blood and helps with clots in my varicose veins. I have been doing other things to help the veins so stopped the 2 grams of fish oil a day for about 60 days.
I’ve had horrible problems with inflammation for quite a while and mostly manage it through diet and exercise. But over the last 4 weeks I could not get the swelling in my left leg to go down. I was miserable, My joints were getting achy again and I was very moody. Signs of inflammation for me.
My husband asked me to try taking the fish oil again. I started taking it again 3 days ago and the swelling is gone and I feel so much better. Apparently I need the fish oil. I eat a very healthy diet so something in me needs that combo. I will continue the 2 grams a day with plenty of antioxidants.
I think for some of us we just need the higher levels of Omega 3s.
Carolyn your observation is very interesting for me.
I too suffer from varicose veins and I managed to successfully go through my third pregnancy without taking any anticoagulants, just 10 ml of FCLO along with BO.
Three years ahead I’m still managing my veins with 5 ml of FCLO and Dr. Mercolas K2.
But recently, after Chris’ recommendations I switched to Rosita’s evclo, and the health of my veins deteriorated significantly, there were obvious signs of inflammation and pain/ itching/ eczemas on my legs.
When I realized that it must be the oil I switched back to FCLO and recovered!
I’m still not quite sure why this was the case, but if anybody here has an idea I’d appreciate it if you let me know.
I mentioned tinned salmon in a reply earlier. Has the preparation of tinned fish spoiled many of its benefits? I buy tinned Wild Pacific Red Salmon and Scottish Mackerel in Olive Oil and regard them as the protein part of a meal. Smoked fish gives me a headache, though it’s hard to resist smoked salmon sometimes! Smoked mackerel once gave me such a severe headache that I’ve never dared to try it again; I’ve always believed that it is notorious for this.
You many have a histamine intolerance. Smoked and canned fish is famous for being high histamine. Google it and see if it applies to you.
I find that it’s cheaper to buy a high quality cod liver oil (such as Carlson) than to buy fish (at least, where I live). I live in the Maritimes, and yet fish is outrageously priced. I buy it when it’s on sale at the same price as cheap ground beef or pork. That ranges from $2-$3.50 lb. Normally, it’s about $7 a lb (at cheapest). I can’t afford that!!!
My husband’s HDL is 100. We think it has to be the fish oil. He has been taking it for a long period of time. It seems to help him.
Perhaps, modern researchers should concentrate on the effects of excess omega-6’s rather than a deficiency of omega-3’s. The ratio between the two is all important for long-term health.
It’s the adulteration of Omega-6 by processing that has made them dangerous, not the ratio.
Really, not the fact that historically we ate them in about a 2:1 ratio and now most eat them in about a 20:1 ratio?
Try and find any prepared food that doesn’t have canola, soy or corn oil in it. The reason food doesn’t rot on the shelf is the same reason it causes cellular inflammation, the inability to absorb oxygen, a vital function of cellular and mitochondrial membranes that is significantly dependent on proper 18 carbon Omega-6 (Linoleic acid)
I’ve been taking relatively high doses of fish oil supplements for the last 2 years, less for the other health benefits I’d read about and more for anti-inflammatory reasons. I’m an avid weightlifter and have read various articles about the ability of fish oil to help reduce overall inflammation. Anyone seen any good research on this?
For scientific studies check out:
http://www.expertomega3.com/omega3-studies.asp
http://www.omegaquant.com/
http://www.omegametrix.eu/literaturverzeichnis_hsomega3index.html?lang=EN
For ways to test Omega-3 Index & Omega-6/3 ratio:
http://greenvits.eu/pages/omega-3
My ND prescribed 1G fish oil a day for helping reduce overall inflammation in body (I had an issue with hives last year) – would this help? Thanks so much Chris!
I’ve always been reluctant to take fish oil for various reasons. I’m not really into eating fish, either. Never liked it. But fish oil has been touted for a long time, so I tried.
I’ve purchased many brands and many types over the years, including CLO, krill, etc. etc. Every brand and type of fish oil I’ve tried – even the so-called “no burp” oils, give me indigestion. I’ve wasted too much money trying to find the right fish oil for me.
So we decided to eat canned sardines instead.
I tried a high-fat, low/moderate-carb paleo diet a couple years ago, but determined I am one of those who is hypersensitive to dietary fat. My LDL shot up almost 50% from a 4-year average of 110 to 158 in six months. No surprise, but I was concerned that my LDL-P jumped 80% from 1015 to 1832. I am ApoE 3/3. My Lp(a) is always above 220 except when it dropped to 194 from the high fat diet.
Going back to a more moderate diet has helped everything, but my LDL-P was still elevated at 1482 last month. I take a tsp of FCLO every day and had doubled up on krill oil before this last test. Since this last test I have stopped all krill oil and olive oil to see if that helps.
Are there any studies connecting fish oil to LDL-P?
The LDL hypothesis of heart disease has never been proven in any credible study. I would stop measuring it.