The mercurial effects of exercise

An international group of public health researchers found that fitter study participants had better general brain function, could process information faster and had enhanced short-term memory compared to less fit participants. However, these benefits did not extend to individuals who were exposed to high levels of mercury before they were born. But don’t take this research, reported in the journal Environmental Health Perspectives, as an excuse to lay off the cardio.

Scientists gave the study participants, a group of young adults from the Faroe Islands, several cognitive tests, then measured how much oxygen they took in during aerobic exercise as a test of their physical fitness. They also looked up how much mercury had been in the blood of their umbilical cords, which scientists carefully recorded in 1992.

The Faroese are at higher risk of mercury exposure than most of us because they eat a lot of seafood. Ocean fish and mammals at the top to the food chain, such as whales, sharks and swordfish, are more likely to contain elevated levels of mercury, according to a 1998 study in the journal Environmental Research. The scientists who worked with the Faroese mothers in 1992 noted that “frequent ingestion of whale meat dinners during pregnancy” increased the chances that the women’s hair and their children’s umbilical cord blood would contain high levels of mercury.

Those of use who live elsewhere should also be cautious about mercury exposure. Even low doses of mercury can still have negative health effects, according to a study in the journal Environmental Toxicology and Pharmacology. Shark, swordfish, and tilefish all contain elevated levels of mercury — the average person shouldn’t eat more than about six ounces a week, according to the U.S. Environmental Protection Agency. Pregnant women should probably avoid these fish completely.

Scientists have linked mercury exposure to heart disease, reproductive issues, nerve disorders, and even neurological problems such as Alzheimer’s and Parkinson’s disease.

But even if mom craved seafood while pregnant, that’s not a reason to throw your running shoes in the dumpster just yet. The point of exercise is not only to improve cognitive function — it helps prevent obesity, diabetes, and heart disease, too.

So even though eating the meat of large fish isn’t a good idea for pregnant women, it’s still worth emulating how much the fish exert themselves. Swordfish can swim 50 miles an hour, for example, and humpback whales travel nearly halfway around the world each year. “You are what you eat,” as the saying goes — but you don’t have to eat fish in order to work out like they do.