Is Mercury in Fish Really an Issue?


If you're like me, you face a bit of a conundrum when deciding whether or not to eat ocean fish. On the one hand, fish is a very healthy source of essential fatty acids and protein. On the other, we are routinely told to avoid certain species and not over-eat because of contamination with highly toxic mercury. I would like to let you in on some very interesting research that I came across, recently. As it turns out, there's a little more to the story - even if a fish does contain mercury, it may still be worth eating while on your teatox. Read on to find out why. 

What's up with Mercury?
First, let's just go over why mercury contamination exists and why it's bad for you. Mercury is a natural element found in very low concentrations in the natural environment and living organisms. It has not really been a problem until the last few centuries of human industrial activity (e.g., coal-fired electricity generation, smelting and the burning of waste), which pumps mercury into the air. This eventually falls into lakes, rivers and the ocean, where it is consumed by fish and other marine life. Fish store mercury in their bodies and it becomes more concentrated as you move up the food chain - bigger fish store more than smaller fish.

Mercury can be problematic for humans in many ways. It's especially dangerous for developing babies since it can interfere with brain and nerve development, leading to lower brain function. In adults, it can affect fertility and blood pressure regulation and can cause memory loss, tremors, vision loss and numbness of the fingers and toes as well as other neurological disorders. In short, mercury poisoning is a serious problem. 

Should we Avoid Fish?
General consensus in recent years has been that ocean fish contain mercury and we (especially pregnant women) should avoid consuming it more than once a week or so. However, such concerns are unfounded and not supported by the science most of the time. In fact, we could say that the benefits of eating cold ocean fish far outweigh the risks for mothers to be. Omega 3 fatty acids are crucial for the development of the infant brain and nervous system. And, eating plant sources of omega-3 like flax or walnuts doesn’t cut it, because only a very small percentage of the omega 3 fatty acids are taken up by the mother's body. 

But what about the mercury? The worry for mercury came from a few scientific studies. They saw that people in cultures who ate a lot of fish tended to have higher mercury buildup in their tissues, and concluded that this was directly the result of consuming a lot of mercury-containing fish. However, what was missing from these conclusions was the fact that not all "fish" are made equal. Some have more selenium than others.

What does selenium has to do with this? Well, it's another naturally occurring element that is abundant in the ocean, and it happens to be crucial for fighting oxidation (damage) in our tissues. It also happens to help prevent damage that may be caused by mercury. So, as long as you are getting enough selenium, you should be able to counteract mercury toxicity. 

What's important to know is that the selenium to mercury ratio in aquatic food varies. Most ocean fish have more selenium than mercury, which means that they are safe to eat. Larger ocean animals, such as sharks and whales have more mercury than selenium, which means they are not safe to eat. Remember the studies on fish consumption and mercury buildup I referred to above?  It turns out that these populations typically ate a lot of shark or whale meat. This is really why they had higher mercury wasn't the fish. The safety of fresh water fish can be a little harder to determine. It really depends on how much selenium and mercury is available in the surrounding environment. For example, lake fish in an area rich in selenium and little industrial activity will likely have a favourable selenium to mercury ratio. The opposite is also true and, as you can imagine, it takes a lot of scientific measurements to determine if one lake is healthy while another is not.

Is mercury in fish really an issue?

Yes - it is an issue in the sense that human industrial activity is polluting the environment and adding another toxic chemical that is undermining the resilience of nature. It is also a health issue if you eat some large predatory ocean animals (e.g., whales and sharks) as well as some fresh water fish. This is because of the unfavourably low selenium to mercury ratios in their tissues.

No - Mercury is not a major health issue if the fish in question is an ocean fish with a favourably high selenium to mercury ratio. So, go ahead and eat cold water ocean fish. The health benefits far outweigh the potential costs according to scientific study. However, be a little more cautious eating fresh water fish, and avoid shark and whale meat!

This blog post only scratches the surface. If you want to learn more, I strongly recommend listening to a leading expert,  Dr. Nicholas Ralston on this podcast. You can also watch this video by the Energy & Environmental Research Center 


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