I was watching TV last night when a program about mercury levels in tuna came up. I eat a lot of tuna here so I was really interested in what they had to say. They had some interviews with Americans and Japanese people and their experiences in their own countries with Mercury poisoning. One American woman did some unscientific research for a news station. She ate one can of tuna every day for twenty days. After 10 days the mercury levels in her blood stream were elevated and by day 17 her blood mercury level had already reached a point where, if she had been pregnant, she could have been putting the baby at risk for birth defects. Her doctor urged her to end her little experiment.
Just eating tuna for 17 days straight to get mercury poisoning is a little frightening. They had another man who was a bicycle racer. Because of his lifestyle he needed to eat a lot of protein. He ate tuna often because it was cheap and easy. Then he started to have health issues like fatigue and dizziness and he fell off his bike while riding. His doctors diagnosed him with mercury poisoning.
After that they showed some Japanese people who had suffered from high levels of mercury from their mother's womb. The mercury caused severe developmental defects.
They showed some graphs (in Korean) about levels of certain fish. Large tuna was among the highest, since they are very high up the food chain. But, the program told worried Koreans not to worry about Korean canned tuna. The tuna that Koreans use to make canned tuna is generally from smaller tuna, which are not as high up the food chain, and therefore containing less mercury.
Now, if this is true, it makes me feel a little better about eating the amount of tuna that I do... I would say I eat tuna 1-2 times per week, sometimes more here in Korea. But, on the other hand, it makes me wonder about the fishing practices of Korean fishing vessels. If they are fishing for young tuna, they are not letting them get to reproductive stages and therefore contributing to lowering the tuna population.
American canned tuna, on the other hand is generally made from fully grown tunas. These tuna generally have dangerously high levels of mercury and, like the woman I mentioned, if you eat tuna often, you are putting yourself at risk of mercury poisoning. And if you are pregnant you would be putting your baby at serious risk for developmental problems.
More information here from PBS
Wish I could find more info about Korean canned tuna, but I would expect that info to be in Korean on the web...
Top photo was taken by me in the Tsukiji Fish Market in Tokyo