One of my patients recently asked me if pregnant women can eat fish. I love fish – low in saturated fats and high in omega 3 fatty acids, it’s a great source of heart-healthy protein. I grew up on the coast and as a child was lucky enough to be able to eat beautiful fresh fish. So no-one is more disappointed than me that so many fish are too contaminated to be safe. However the health benefits outweigh the concerns for me and I do still eat fish. I’m just very careful about the kinds of fish I eat.
So what is mercury and how does it get into the fish? Mercury is an element that occurs naturally in soil, lakes and oceans. Although some mercury is natural, mercury is also released into the environment from man-made sources. These include power plants that burn coal as well as waste incinerators, paper processing factories, mines and smelting operations. The mercury gets into the air as pollution and then goes into the water when it rains. Surface run off can also dump mercury into our lakes and oceans. Once there it settles at the bottom of the ocean where it is converted into methyl mercury by bacteria. It is this methyl mercury that is more toxic unfortunately. Fish absorb the methyl mercury in two ways, both as food and in the water as it passes through their gills. The mercury then binds to proteins in the muscles of the fish.
All fish contain some mercury and there is no way of cleaning the fish that avoids this. The amount of mercury accumulates as you move up the food chain so the bigger, more predatory fish contain much more. There was a 163% increase in mercury advisories issued by the EPA between 1993 – 2003 so its not hard to see that the amount of mercury in fish is going up.
Taking in too much methyl mercury can cause some serious health problems. When we eat fish it is absorbed through the intestines and spreads throughout our bodies. It enters the brain in the blood stream and can effect the nervous system. It can also cross the placenta to effect an unborn child or be passed through breast milk to an infant.