“Eat fish! It is an excellent source of protein, it is great for heart health and is high in much needed Omega 3 oils.” How many times have you heard this? It is true that fish has wonderful health benefits but it can often harbour a secret that ought to make you think twice about how much you consume.
The reason for caution is that fish is often high in mercury, in the form of methyl-mercury. It is a contaminant found in varying level between fish species due to factors such as type, size, location, habitat, diet and age.
A friend of mine once spent time in Hong Kong and told me that common Hong Kong folk law said that there was so much mercury in Hong Kong harbour that the fish took their own temperature. It gave us a laugh, but there is truth behind the humour.
How does mercury get into the fish in the first place?
Mercury occurs naturally in the ocean sediment but can also occur as contamination as a result of human activities. Micro-organisms transform the mercury in methyl-mercury and it bio-accumulates in aquatic organisms. What bio-accumulation actually means is that when a larger fish eats a smaller fish, it accumulates the level of methyl-mercury that the smaller fish contained. When it eats another smaller fish, it accumulates some more methyl mercury. The more small fish it consumes, the more methyl-mercury it accumulates and the level does not drop. Then along comes an even bigger fish and eats the fish that ate the smaller fish and that larger fish accumulates all the mercury of the fish it just ate and so the vicious circle continues.
Fish not only accumulate mercury from consuming smaller fish. All fish absorb methyl-mercury from the water that passes through their gills. The longer the fish lives, the more methyl-mercury it will bio-accumulate. Fish that are not predatory and are short lived are not going to contain as much methyl-mercury as their predatory and long living relatives so these are the fish we want to be including in our diet.
Why should we be concerned about mercury in fish?
Just as the methyl-mercury bio-accumulates in fish, it bio-accumulates in humans. Our biological systems are not adequately designed to cope with this type of contaminant so it bio-accumulates in our bodies. As it bio-accumulates, it needs to be stored somewhere and it is stored in our fat tissue, brain and bones. It contributes to what I call the toxic load on our bodies which increases daily contributing to the general loss of vitality that affects the general population.
Over time, our bodies can remove the methyl-mercury. However, it is difficult for the body to remove the methyl-mercury when it is faced with more methyl-mercury entering the body faster than it can remove it. Our bodies were never designed to cope with the toxic load it is presented with every day in our current environment. The toxicity our bodies cannot remove today, it will store with the idea that perhaps tomorrow it will be able to deal with it — but tomorrow never comes. It is why looking at simple, everyday detox solutions to help your body is so important. If you want more information in this area, my contact details are listed below.
The major concern with methyl-mercury is related to the potential affect on the nervous system and especially the developing foetus. Raised mercury levels in the mother can be passed through the placenta to the developing baby.
The foetus appears to be most sensitive to the effects of mercury during the third and fourth months of a pregnancy. The effects on the brain and nervous system may not be noticed until developmental milestones – such as walking and talking – are delayed. Memory, language and attention span may also be affected.
Should we limit the amount of fish we eat?
The answer to this question is ‘definitely’. This is especially important for anyone who is pregnant, or wanting to conceive, especially within the next six months.
Avoid the following fish that are known to contain higher levels of mercury:
- Shark (flake in the fish and chip shops)
- Orange roughy
- Southern bluefin tuna
Limit other fish, such as tuna steaks, to one portion per week or two 140g cans of tuna per week (smaller tuna contain less mercury). Salmon, including canned salmon, can be consumed more frequently.
Breastfeeding, Infants and Children
The official line is that mercury levels in mother’s milk are not high enough to pose a risk. As you will read in the last paragraph, I have my personal concerns regarding this statement. I prefer the cautionary approach and recommend adhering to the same guidelines as those for pregnancy.
As for infants and children, avoid the high mercury fish. Their developing systems can do without the burden of having to detox or store methyl-mercury.
My personal opinion on mercury in fish
This is where I stick my neck out and tell you what I actually believe. I may not have real scientific evidence for my beliefs, but an absence of scientific evidence doesn’t mean that all is OK, it just means there is an absence of scientific evidence.
As I mentioned before, I question methyl-mercury levels in breast milk. I don’t care much for the line that the levels are not high enough to be at risk. I want to give babies the best chance and any way we can reduce their toxic load gets a big thumbs up from me. Keep to the pregnancy option if you need to eat fish.
On the side of extreme caution, I have friends in the natural health field that remove all seafood from the diet of women who want to conceive or who are pregnant. They get their omega 3 from flaxseed oil.
I personally do not think that canned tuna is all that safe for women who want to conceive and especially those who are pregnant. Who really knows what sort of tuna is in the can to start with?
I do not believe methyl-mercury only affects fish, it is all seafood. Perhaps we all need to think just a little more about what we eat.
On a totally different, yet related subject, I also query the health benefits of salmon as freshwater fish may contain more mercury than saltwater fish.
Fish that is farmed also concern me as I don’t believe they are fed a diet in keeping with what they should be eating naturally. It seems to me a bit like battery hens versus free range chickens.
When all is said and done, lets not go overboard in the other direction and give up seafood forever. If we help our body every day, it can lower its toxic load then the methyl-mercury can be removed and it will not bio-accumulate. We cannot stop eating, drinking and breathing. Not eating what we enjoy is not fun. Just become more aware of what you put into your body and explore the possibilities that can help your body reduce its toxic load.
For those who want to conceive, are pregnant, breastfeeding, feeding infants and children, keep to the guidelines of avoiding predatory and long living fish as indicated above.
For the rest of the population, be aware of how much seafood you do consume and implement some detox solutions to help the body cope with the methyl-mercury.
Resources and further information
- Too much mercury in freshwater fish
- Mercury in fish – Australian and New Zealand food standards
- Mercury in fish — Better Health Channel
- EWG’s Fish List
- EWG’s tuna calculator