In an attempt to gauge just how dangerous the mercury in fish is, writer David Ewing Duncan decided to measure his blood levels of the toxic metal both before and after gorging on various types of fish.
Mercury is a naturally occurring metal, but one that is highly toxic to the nervous systems of vertebrates, including humans. Studies have shown that it can cause damage to brain functioning, including memory, learning and behavior, and that it can also harm the heart and immune system. The developing nervous systems of children and fetuses are particularly susceptible to its effects.
Fish carry high body burdens of the metal because most of the mercury ejected into the air by the burning of coal eventually ends up in the ocean. There it is absorbed by plankton, which is eaten by successively larger forms of sea life all the way up the food chain to many of the animals commonly eaten by humans.
The EPA has set a maximum safe mercury blood concentration of 5.8 micrograms per liter. But critics allege that there is simply not enough understanding of the way that mercury interacts in the body to back this up.
“No amount of mercury is really safe,” said mercury expert Leo Trasande of the Mount Sinai School of Medicine.
Further complicating matters, some people are more likely to absorb mercury into their bodies than others.
“Toxicologists say that ‘the dose makes the poison,’” mercury expert Jane Hightower said, “but it’s clear that some people are more sensitive to even small exposures than others.”
To test his own susceptibility, Duncan carried out two different “fish gorge” experiments, one in 2006 and one a few years later. In the first, he found that eating store-bought fish caused his mercury blood levels to spike from 5 micrograms per liter before the meal to 12 micrograms per liter afterward. In his second experiment, two meals of wild-caught halibut sent his blood levels from 4 micrograms per liter to 13.
Concentrations as low as 5.8 micrograms per liter in can produce lower IQ scores in children.
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