Omega-3 is vital for a healthy body and mind. But high levels of ocean pollution can make it difficult to know whether it is safer to get this essential fatty acid from fish or from supplements.

Omega-3 is an essential fatty acid, which means it needs to be obtained from our diet, as our bodies are unable to synthesize it. It is important for normal metabolic function, and research suggests that maintaining correct levels can provide a whole host of other health benefits, including reducing the risk of cardiovascular disease, certain cancers, mental health disorders and inflammation.

There are three types of omega-3 that are important to humans. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are found in fish and are the two compounds purported to have the greatest health benefits. The other, alpha-linolenic acid (ALA), which comes from plants, doesn’t provide the same beneficial effects in relation to many health problems, according to epidemiological evidence.

The consumption of fish is considered a key component of a balanced diet, and the current UK recommendation is two portions per week, one white and one oily. This target would provide us with approximately 0.45g/day of omega-3 fatty acids1. However, despite this modest recommendation, the current average for fish consumption is well under this target, at only about a third of a portion per week2.

We know that eating fish can provide our bodies with the omega-3 it needs to achieve optimal health. So why is the recommended weekly target of fish consumption so low considering the multitude of reported health benefits associated with this essential fatty acid?

Pollution

The tissues of many species of fish are found to have elevated metal concentrations exceeding the nationally, and internationally agreed, quality standards for fish and meat, so eating large quantities of fish can potentially lead to increased consumption of these heavy metals which can negatively impact health.

The concentration of metal in fish occurs from contaminated suspended matter in the water and sediments, and from organisms that fish eat. The uptake of metals also plays a role in the reduction of species diversity, because metal-tolerant species become dominant due to their ability to survive with higher levels of heavy metals in their bodies3.

Mercury and arsenic are two toxic compounds that have been shown to bio-accumulate within certain species of fish. These elements have no beneficial effects in humans, and there is no known homeostatic mechanisms related to them. With the exception of occupational exposure, fish are acknowledged to be the single largest contributor of mercury in humans4.

Levels of mercury in fish have been shown to depend largely on fish age and position in the food chain. This means that older, fatty predatory species such as tuna, halibut, redfish, shark and swordfish will be likely to have higher mercury concentrations. Tuna in particular have the ability to accumulate large amounts of mercury, with a majority of it stored in internal organs and muscle5.

There are many negative health outcomes associated with elevated mercury levels. It has been found to play a key role in various disorders including neurological, immunological, motor, reproductive and even genetic. Recently it has also been linked to diseases such as Alzheimer’s, Parkinson’s and autism6.

Plenty of fish in the sea

The levels of heavy metals present in some fish makes it difficult to determine whether fish consumption is the safest way to reap the health benefits associated with Omega-3s. The potential for harm from these heavy metals can point us toward eating less fish known to accumulate mercury, and eating a wide range of safer species.

Without being a complete substitute for fish in the diet, fish oil supplementation may offer a safe method of ensuring adequate omega-3 fatty acid intake. As methyl mercury is water-soluble, mercury and other heavy metals stay behind in the liver, flesh, intestines and other parts that are left behind, when oil is extracted from the fish7. As an independent analysis of 16 different fish oil products has found, no significant heavy metal contamination remained in any of the products tested8.

Within the body DHA is found in the highest quantities compared to other omega-3 fats, with most organs containing up to 30 times that of EPA. Plasma DHA saturation has been shown to occur at approximately 2g per day, with a large number of studies suggesting this figure as a safe amount as a daily supplement.

When choosing a fish oil supplement it may be difficult to identify the better brands, and which have higher levels of EPA and DHA, or are free from potential contaminants. The International Fish Oil Standard (IFOS) is a third-party independent laboratory that tests products to establish a rating and posts all results on its website.

Don’t be lured by the term ’pharmaceutical grade’ on any fish oil supplement. Manufactures often advertise their product with this phrase but no formal FDA definition exists. This is because there must first be an established pharmaceutical standard against which the substance can be measured, and this does not exist for fish oil. So this phrase is used to describe the strength of the product, not the quality.

Krill oil as an alternative?

An alternative omega-3 supplement to fish oil is krill oil. Krill are a small shrimp-like crustacean and may provide a safe choice because they are at the bottom of the food chain, therefore do not have time to accumulate dangerous levels of toxins. Krill oil contains a lower concentration of EPA and DHA than fish oil, but research suggests comparable findings on its beneficial effects on inflammation and oxidative stress.

One issue with krill however, is that they contain enzymes within their digestive tracts that cause them to deteriorate rapidly once caught, so processing must occur at sea which comes with potential logistical and financial implications. There have also been potential ethical concerns related to the harvesting of krill because of their position as a primary food source in the aquatic food chain.

While in an ideal world we would obtain the Omega-3s we need from eating more fish, individual preferences as well as heavy metal contamination may mean that a high quality fish or krill oil supplement could provide an important boost to our levels without the risks associated with metal exposure.

References

  1. Scientific Advisory Committee on Nutrition (2004) Advice on Fish Consumption: Benefits and Risks. London, FSA
  2. Scientific Advisory Committee on Nutrition (2004) Advice on Fish Consumption: Benefits and Risks. London, FSA
  3. R. Dallinger, F. Prosi, H. Segner, H. Back (1987) Contaminated food and uptake of heavy metals by fish: a review and a proposal for further research.Oecologia. Volume 73, Issue 1, pp 91-98.
  4. D. Bahnick, C. Sauer (1994) A National Study of Mercury Contamination of Fish, Chemosphere, 29, pp. 537–546.
  5. Oehlenschläger, J., (2002): Identifying heavy metals in fish. In: H.A.Bremner (ed.): Safety and quality issues in fish processing. 95-113.
  6. F. Zahira (2005) Low dose mercury toxicity and human health. Environmental Toxicology and Pharmacology. Volume 20, Issue 2, pp351–360.
  7. Harris, W (2004) Fish oil supplementation: Evidence for health benefits. Cleveland Clinic Journal of Medicine vol. 71 3 208-210.
  8. Consumer Reports, 2003
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