I've heard people say that pregnant women shouldn't eat a lot of fish because of the mercury content. What's so bad about mercury and why is it in fish?
Although fish contain high-quality protein and other essential nutrients, are low in saturated fat, and contain omega-3 fatty acids, nearly all fish and shellfish contain traces of mercury.
Mercury occurs naturally in the environment, and can also be released into the air from pollution. The mercury falls from the air and accumulates in oceans, lakes, and rivers. Fish absorb the mercury since they live and feed in these waters, and the mercury builds up their bodies. That's why larger fish are the ones to watch out for when it comes to mercury, because they've had more time to accumulate it.
Some fish and shellfish contain higher levels of mercury that may harm an unborn baby or young child's developing nervous system. That's why nursing mothers, women who are pregnant, and those who are trying to become pregnant are advised to watch their mercury intake.
For everyone, elevated levels of mercury can lead to nervous system problems with brain or nerve damage. Mercury levels can be measured by blood tests, or tests using hair.
If you regularly eat types of fish that are high in mercury, it can accumulate in your blood stream over time too. The body naturally removes it, but it may take over a year for levels to drop back to normal. That's why it's important for women who are trying to get pregnant to think about their mercury intake beforehand.