Omega-3 EPA and DHA: problems of fish consumption and better sources for our health and the environment

This article is the third from a series of 3 scientific facts based articles I wrote about omega-3. If you haven’t read the other two:

– the first article is about why some types of omega-3 are so important for us

– the second article is about the conversion from a plant-based omega-3, alpha-linolenic acid (ALA), to other two types of omega-3, eicosapentanoic acid (EPA) and docosahexanoic acid (DHA).

In this article, I will write about the current problems of fish consumption and also about the pros and cons of three types of EPA and DHA supplements. I will then tell you what is, in my opinion, the best source of EPA and DHA nowadays, taking into account health and environmental factors.

Fish is obviously the most common food source of EPA and DHA. However, depending on the amount and on the fish you eat, fish consumption might neither be healthy nor sustainable. Let’s see why.

Problems of fish consumption

Fish was once a very healthy and quite sustainable source of omega-3 fatty acids. You probably have already heard of the benefits of the Mediterranean diet, in which fatty fish was a staple food. However, this is not the case anymore: nowadays, fish is neither super healthy, nor sustainable. And why is that?

Of course fish still contains EPA and DHA, and you will probably have enough of these omega-3 fatty acids if you eat fatty fish 2-3 times a week. However, you can be sure that you will also get your dose (or big dose, depending on the fish) of highly toxic pollutants. We should take into very serious consideration that our oceans are full of mercury and other heavy metals, plastics as well as polychlorinated biphenyls (PCBs) and other pollutants.

PCBs are dangerous pollutants present in fish (and also found in dairy, hamburgers and poultry), that can lead to long-term neurological, immunological and hormonal problems: increased rates of autoimmune diseases, cognitive and behavioral problems, hypothyroidism as well as a reduced ability to fight infection [1]. Also, they seem to be a risk factor for type 2 diabetes [2]. A recent prospective study also demonstrated that women with the highest PCB exposure had almost 3 times the risk of having an hemorrhagic stroke compared to women with the lowest exposure [3]. Exposure to PCBs is particularly dangerous for the fetus. For example, a study published in the Lancet found that prenatal PCBs exposure inhibited mental and motor development [4]. Many other studies have also demonstrated several detrimental effects of PCBs, as reviewed in [1].

As you may know, mercury is a neurotoxin [5, 6] (meaning, is toxic for the brain), that is present in fish and that can be particularly detrimental to the fetus and children [7-11]. Studies have been showing that the more fish you eat, the more mercury can be detected in your hair [12, 13]. Beyond mercury, people who eat a lot of fish have also increased blood levels of arsenic and lead [14].

So, does the omega-3 content in fish compensate for its high toxic load? Well, it will of course depend on the amount you eat and which fish you eat, as in general, the larger the fish, the longer it has lived and the more toxins it accumulated. While some studies showed that eating fish regularly could be beneficial for preventing some diseases, others showed no association, or even a detrimental effect of fish consumption. Scientists have proposed that the inconsistent findings on the effects of fish consumption on human health by several studies might be due to the harmful contaminants in fish [15].

An interesting study on fish consumption during pregnancy compared the risk-benefit of fish consumption for the child – benefit due to the presence of DHA and risk due to the presence of mercury [16]. They measured the mercury and DHA content of 33 fish species and studied the net effect of these compounds on the kids’ IQ score. In their own words:

For most fish species the adverse effect of MeHg [methylmercury] on the IQ score exceeded the beneficial effect of DHA.

But some fish species were particularly worse than others: long-living predators, like tuna or swordfish, which have a very high mercury content, had the worst effects on IQ [16]. On the other hand,  smaller fishes, like wild salmon, sardines, herring and mackerel, had a neutral or even a small positive effect [16].

However, there is another way you can get all the benefits of omega-3 fatty acids without being exposed to toxic compounds, as I will explain below.

Besides pollutants, there are also serious environmental and sustainability concerns with fish and fish oils intake.  It has been considered by many scientists that this is not a sustainable long-term approach [17] to increase our EPA and DHA levels as the world’s fish stocks are declining [18]. Aquaculture (fish farming) has also been used as a source of fish for consumption, but this practice has been associated with damage to and pollution of sensitive ecological areas [17, 19].

EPA and DHA supplementation

As I explained in the previous article, ALA can be converted into EPA and DHA, although the conversion rate is low and depends on several factors, also mentioned in the last article. However, depending on the health situation you are going through, an omega-3 supplement might be beneficial. These situations could be for example:

pregnancy, as DHA is crucial for the developing brain (but not all DHA supplements are beneficial, please read further below)

a specific health issue. I suggest you first talk to your doctor, but indeed several studies have shown that EPA and DHA can be beneficial to many diseases. For example, EPA has been shown to be particularly helpful in decreasing inflammation in rheumatoid arthritis [21, 22], in fighting depression [23, 24], and DHA seems to be important for cognition and slowing down cognitive impairment [25]. In fact, Alzheimer’s patients have been reported to have too little amounts of both EPA and DHA in their brain [26], although it is still not known whether this is part of the cause or one of the consequences of the disease.

if you don’t eat fish: as mentioned in the last article, DHA levels are lower in people who do not eat fish regularly. However, vegans and vegetarians have no clinical signs of DHA deficiency, meaning that they don’t have more neurological or cardiovascular disorders than omnivores [27-29]. This could be because the conversion of ALA into DHA is more efficient in this population [30]. However, there are omnivores who do not eat fish as well, and therefore the results could be biased by this fact. Therefore, more research is required to understand whether levels observed in vegetarians are sufficient to support optimal health. This is especially important as lower EPA and DHA levels are associated with smaller brain volumes [31, 32]. So, if you don’t eat fish regularly and you want to make sure that you have enough EPA and DHA, I recommend you do two things:

1- Check your omega-3 blood level status. In general, common labs will not do this analysis. I recently found this company and I think their testing is quite trustable (they don’t sponsor us in any way, I just honestly think they are trustable as scientific studies have been carried out using their test).

2- Depending on your omega-3 levels, you might want to keep your “omega-3” strategy or not (meaning, eating only ALA or SDA -rich foods). If your levels are low, you might want to consider taking an omega-3 supplement. It has been shown that in vegans and vegetarians, when given a DHA supplement, DHA concentration in the blood phospholipids increases dramatically [27] (more information below on this), however long-term studies are still needed to understand whether this increase is associated with actual neurological diseases prevention.

Now, I want to say that not all EPA and DHA supplements are the same, and some have been shown to be more beneficial than others from a health and environmental point of view. So let’s look at what science has been showing on these supplements.

There  are three types of EPA and DHA supplements:

– fish oil

– krill oil

– algal oil

  • Fish oils

As I wrote above, fish is highly contaminated with heavy metals, plastics and PCBs. Fish oil supplements have been supposedly decontaminated, however pollutants have still been found in some supplements [33, 34]. Moreover, studies have found contradictory effects of fish oil intake, for instance, for protecting against heart disease [35]. Beyond contaminants, this contradictory effects might be due to the fact that fish oil supplements are quite prone to oxidation [36]. In this line, it was shown that decontaminated farmed Atlantic salmon oil protected rats from metabolic disorders, but when the same oil was not decontaminated, the presence of pollutants completely counteracted the beneficial effects of the decontaminated omega-3 fatty acids and, in fact, it even accelerated the development of insulin resistance [37].

And, what I mentioned above for fish in terms of sustainability holds also for fish oils (and even more, as higher amounts of fish are needed to produce a supplement): they are not a sustainable long-term approach [17] because the world’s fish stocks are declining [18].

So, it is really important to find other approaches that can meet our omega-3 fatty acid demands.

  • Krill oil

Krill are plankton that ingest algae. Krill oil is a comparable dietary source of omega-3 fatty acids as fish oil [38], but it seems to be a better alternative to fish oils in terms of  sustainability [41] and bioavailability (meaning that, given the same amount, it is more efficient at increasing our blood levels of EPA and DHA than fish oils) [39, 40]. They are also less prone to oxidation as they contain tocopherol (vitamin E) and astaxanthin, which are antioxidants [42]. They can still contain pollutants although the amount vary with each krill oil brand [43, 44].

  • Algal oil

There is also a plant-derived direct source of DHA and EPA:  algal oil. Actually, do you know why fish are a good source of EPA and DHA? Because they eat algae (or other fishes that eat algae)! Algae are at the very base of the food chain for fish!

In the previous section, I said that krill oil has a higher bioavailability than fish oil. But studies in animals have shown that actually algal oil has even an higher bioavailability than krill oil! [45] Algal oil has also been shown to decrease triglycerides, blood pressure and oxidative stress, and to increase HDL and LDL cholesterol particle size (which is a very good thing) [46-49]. It was also very well tolerated by participants in these studies. However, it must be said that there are fewer interventional studies on algal oil than on fish or krill oils.

Because DHA and EPA are essential for the developing brain, but due to the level of contamination of fish, it has been recommended that pregnant women take algal oil supplements rather than fish oil [50].

So, if we balance health benefits, low toxin levels and sustainability, my opinion at the moment is that algal oil and krill oil are the best options, and that fish oils should be avoided.

In vegans and vegetarians, after being given 900 mg per day of algal-DHA for 8 weeks there was a significant increase in DHA levels in blood phospholipids, from 2.8% to 7.3% [27]. So, if you want to increase DHA concentrations in your brain, or you are in a situation that requires extra DHA like certain diseases, or pregnancy, taking extra ALA might not help, but a supplement of algal oil will [51].

So, now, which amount should you take?? Research has been suggesting that a supplement of 200-300 mg/day of DHA and EPA for those with increased needs, such as pregnant and lactating women, and those with reduced conversion ability, such as older people or those who have chronic disease might be beneficial [52].

Did you know that fish has the health and environmental issues discussed in this article? Have you heard before about algal oil? Let me know in the comments below 🙂

I hope you liked these articles and that they brought you new information! 🙂 I would be really happy to have your feedback – positive or negative! The positive ones give us motivation and the negative ones allow us to improve :).


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5 Responses to “Omega-3 EPA and DHA: problems of fish consumption and better sources for our health and the environment

  • Super nice article! Very informational 🙂 could you share the results with me? I am very interested to your plant approach to the omega 3 problem.

  • Anthony Cook
    6 years ago

    Have you heard of the danger of elevating DHA in men with prostate cancer? Experiments have shown a +ive correlation between DHA blood levels and the faster growing type of PC .
    This may also be the case for other hormone sensitive cancers, of which breast cancer is one.
    PC patients are in a difficult situation if this is true (meaning if the results of the study are reliable) – a choice between Alzheimer’s and death by cancer.

    • Ana Coito, PhD
      5 years ago

      Hi Anthony,
      I was not aware of this and found it quite intriguing so I researched a bit. Interestingly, I found studies that show the exact opposite – cell apoptosis (i.e., cell death) as well as inhibition of proliferation, invasion and migration of human prostate cancer cells by DHA and EPA. Could you post here the link to the study you are refering to? It could be that the dose makes the difference, I don’t know but it would be interesting to take a look.

  • Hi Anita,

    Did you ever get your labs, just wondering how you omega-3 ala to to epa /dha conversion was? Also did you recheck your labs after adding the algal oil and do you still recommend algal oil?

    • Ana Coito, PhD
      5 years ago

      Hi Rob, my omega-3 ratio was very low before I started algal oil. But this doesn’t mean that other people’s omega-3 would also be low, our bodies are different and it could be that other people have a better conversion ratio than me. It is always a good idea to check, in my opinion. The other point I want to mention is that at the time I wrote this article, I was not eating any fish and just taking flax seeds (freshly ground) every day. I have now been taking algal oil almost everyday and have also reintroduced some low mercury fish here and there. I want to test my omega-3 again and could post an update once I get the results but my situation now is different anyway as I was pregnant and am now breastfeeding and, as studies have suggested, my omega-3 might be lower now because I am giving it to my baby and not necessarily because I don’t have enough.

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