Salmon has the highest concentration of omega-3 fish oils and a very low concentration of mercury, as shown above. For mercury, this source cited FDA data from here. This number is for farmed salmon. 70% of salmon produced worldwide is farmed . Mercury levels in wild salmon are higher but still low. We will get to that below.
This review found a reduction in all cause mortality:
Six studies with 430,579 participants investigated the association between long chain n-3 PUFA and all-cause mortality risk, the relative risk for highest versus lowest category was 0.86
This review found a reduction in cardiovascular disease:
Numerous PCs [prospective cohort studies] and RCTs [randomized controlled trials] from around the world have investigated the potential effects of fish or n-3 PUFA [polyunsaturated fatty acid] consumption on CVD [cardiovascular disease] outcomes. Meta-analyses of these studies indicate that fish and n-3 PUFA consumption reduce the risk of CHD [coronary heart disease] events, primarily due to prevention of CHD death.
According to this animal study, Omega-3 Fatty Acid Supplementation Reduces Intervertebral Disc Degeneration , fish oil improves the health of injured intervertebral discs. In the test arm they fed rats the human equivalent of 4 grams per day of fish oil, daily. The result:
This study is the first to demonstrate that a n-3 FA [fatty acid] diet of EPA and DHA[the key fish oils] attenuates IVD degeneration in a rat lumbar disc degeneration model. Daily oral supplementation of pharmaceutical grade n-3 FA for 2 months decreased injury-induced dehydration of intervertebral discs and reduced histological signs of IVD degeneration.
This was just an animal study, but there is not much that benefits intervertebral discs. I am contending with sciatica, so this is of interest to me personally.
A more complete list of fish oil benefits, supported by references to the medical literature, can be found here: Beyond Heart Health: More Reasons To Take Fish Oil
As stated above, 70 percent of salmon production is farmed. In a recent investigation, 6 out of 8 samples that were claimed to have been wild caught were actually farmed. So if you are consuming salmon it is likely to have been raised on a farm.
So how bad is farmed salmon? The quality of farmed salmon has improved considerably over the last two decades. Research in the early to mid 2000s found very high levels of POPs – persistent organic pollutants – in farmed salmon, and these levels were a health risk. Since then the salmon farming industry has taken measures to improve this. By 2011 they had reduced levels of POPs by factor of 3, and there been further reductions since then.
According to studies published in the last 5 years, levels of POPs in farmed salmon are now less than wild salmon. This change has been primarily due to terrestrial farming replacing most of the ocean fish that had been used in feed. In addition, nonchemical means of suppressing salmon parasites have been replacing dangerous pesticides.
The best evidence is provided by a recent human study that tested the presence of POPs in humans after consuming over one pound of farmed salmon weekly for 6 months: Effect of fatty fish or nut consumption on concentrations of persistent organic pollutants in overweight or obese men and women: a randomized controlled clinical trial, published in 2019:
Men and women aged 35–70 years with body mass index between 25 and 38 kg/m2 and at least 1 cardiometabolic component were randomized to high intakes of fatty fish (mostly farmed salmon, ∼ 630 g/week; n = 45), high intakes of nuts (∼ 200 g/week; n = 42) or a control group following their usual diet but restricting fatty fish and nuts for 6 months (n = 44). Concentrations of 15 POPs (5 organochlorinated compounds, 2 dioxin-like polychlorinated biphenyls and 8 non-dioxin-like polychlorinated biphenyls) and cardiometabolic risk factors were measured at baseline and end of the study. Results showed that changes in concentrations of individual and classes of POPs did not differ between the dietary groups and controls (p > 0.05). Among cardiometabolic risk factors HDL-cholesterol [the good kind of cholesterol] increased in the fatty fish group compared to controls (+0.10 mmol/L, CI (0.05–0.20); p = 0.005) while no changes were observed in the group consuming nuts.
Conclusion: Fatty fish consumption for 6 months did not increase the serum concentrations of POPs in individuals with overweight or obesity and metabolic risk
The details of the diet:
Participants randomized to the fatty fish group were asked to consume 4 portions (fillets) of farmed salmon provided in frozen portions (a total of 500-560 g weekly) and 1 tin of mackerel in tomato sauce (110 g) weekly.
In this study the consumers of salmon actually showed slight decreases in serum concentrations of POPs, as did the control group.
Here are a couple of recent studies of the levels of POPs in farmed salmon:
Lower levels of Persistent Organic Pollutants, metals and the marine omega 3-fatty acid DHA in farmed compared to wild Atlantic salmon, published 2017:
Contaminants and fatty acid levels in farmed- versus wild Atlantic salmon have been a hot topic of debate in terms of food safety. The present study determined dioxins (polychlorinated dibenzo-p-dioxin and dibenzofuran), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), organochlorine pesticides (OCPs), metals and fatty acids in wild and farmed Atlantic salmon. Contaminant levels of dioxins, PCBs, OCPs (DDT, dieldrin, lindane, chlordane, Mirex, and toxaphene), and mercury were higher in wild salmon than in farmed salmon, as were the concentrations of the essential elements selenium, copper, zinc and iron, and the marine omega-3 fatty acid docosahexaenoic acid (DHA). PBDE, endosulfan, pentachlorobenzene, hexachlorobenzene, cadmium and lead levels were low and comparable in both wild and farmed fish, and there was no significant difference in the marine omega-3 fatty acid eicosapentaenoic acid (EPA) concentration. … Contaminant concentrations in Atlantic salmon were well below maximum levels applicable in the European Union. Atlantic salmon, both farmed and wild, is a good source of EPA and DHA with a 200g portion per week contributing 3.2g or 2.8g respectively...
An Update on the Content of Fatty Acids, Dioxins, PCBs and Heavy Metals in Farmed, Escaped and Wild Atlantic Salmon (Salmo salar L.) in Norway. published in 2020:
In this paper, we present updated data on...concentrations of dioxins, polychlorinated biphenyls (PCBs), and selected heavy metals, in fillets from farmed (n = 20), escaped (n = 17), and wild (n = 23) Atlantic salmon (Salmo salar L.). The concentrations of dioxins..., dioxin-like PCBs ... mercury..and arsenic ... Were three times higher in wild compared to farmed salmon, but all well below EU-uniform maximum levels for contaminants in food. The six ICES (International Council for the Exploration of the Sea) PCBs concentrations (5.09 ± 0.83 ng/g) in wild salmon were higher than in the farmed fish (3.34 ± 0.46 ng/g). ...The fat content of farmed salmon (18%) was three times that of the wild fish, and the proportion of marine long-chain omega-3 fatty acids was a substantially lower (8.9 vs. 24.1%). The omega-6 to omega-3 fatty acid ratio was higher in farmed than wild salmon (0.7 vs. 0.05). Both farmed and wild Atlantic salmon are still valuable sources of eicosapentaenoic acid and docosahexaenoic acid. One 150 g portion per week will contribute to more (2.1 g and 1.8 g) than the recommended weekly intake for adults
All the foregoing studies took place in Norway, and it was the source of the salmon being studied. It turns out that Norway supplies more than half of the world's farmed salmon. What do we know about other sources? First, note that almost all farmed salmon is Atlantic salmon:
(The following charts are from the Salmon Farming Industry Handbook 2022)
Between them, Norway and Chile supply about 85 percent of the market:
The proportion of vegetable sources in salmon feed is very similar for both Norway and Chile:
The substitution of vegetable sources for animal sources reduced the POPs in Norwegian salmon. We see here Norway and Chile have similar composition of salmon feed. Therefore the POP contamination in Chilean salmon should be similar to that of Norway. Not as good as direct evidence, so we make do with the data that is available.
POPs are not the only contaminant of concern. There is the matter of ...
The Mercury reference: A Quantitative Synthesis of Mercury in Commercial Seafood and Implications for Exposure in the United States
Methods: We developed a database of Hg concentrations in fish and shellfish common to the U.S. market by aggregating available data from government monitoring programs and the scientific literature. We calculated a grand mean for individual seafood items, based on reported means from individual studies, weighted by sample size. [Emphasis added]
Note that weighting by sample size is not the same as weighting by amounts produced.
The FDA action level for MeHg of 1.0 ppm represents the threshold above which the agency can take legal action (e.g., removing the product from the marketplace) ... The U.S. EPA MeHg criterion of 0.3 ppm represents the fish tissue concentration that should not be exceeded for safe consumption of sport-caught fish in local waters based on average consumption
Salmon detail, from the supplemental material:
At .026 ppm, farmed Atlantic salmon mercury content shown here is higher than the level noted in the title image at top, but is still among the lowest of all fish sources. The sample weighted average of .048 is heavily weighted by wild salmon. Even so this is lower than 1/6th of the safe consumption limit ,and even the worst case is still lower than the safe consumption limit of .3 ppm.
Safe consumption levels per the Environmental Defense Fund
A complete account of the depredations of the salmon farming industry can be found in the book Salmon Wars The Dark Underbelly of Our Favorite Fish.
Here we will focus on pesticide use which probably has been the worst environmental offender. The pyrethroids cypermethrin and deltamethrin have been used by salmon farms to combat salmon lice, a chronic pest. These substances are highly toxic to other aquatic organisms. They are also associated with a high risk of Parkinson's in exposed humans.
Among the sins set forth in Salmon Wars, in 2009 Cooke Aquaculture illegally used cypermethrin to control salmon lice in the Bay of Fundy, and as result killed at least hundreds of lobsters. The principals faced criminal charges, but in the end the company settled the matter by paying a fine.
Fortunately there is some good news on this front. From Trends in de-lousing of Norwegian farmed salmon from 2000–2019—Consumption of medicines, salmon louse resistance and nonmedicinal control methods, per the below chart, as of 2019, the use of cypermethrin in Norway was down to zero and deltamethrin usage was less than a 10th of the peak and falling. (I searched for information on deltamethrin residue in salmon but was unable to find any). Nonchemical salmon lice treatments are now being applied in Norway at 3 times the rate of chemical treatments. Also, in Canada, in 2021, 56% of sea lice treatments were nonchemical, compared with 12% in 2015.
So it would seem that it is safe and beneficial to consume salmon, even the farm raised version.
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