Fish accounted for just 7 percent of the mercury measured in a group of pregnant women’s blood, found a new British study, whose authors argue that the benefits of eating fish during pregnancy appear to outweigh the costs.
And while those conclusions have received a fair dose of media attention with pro-fish headlines, other researchers continue to urge caution.
Among the study’s shortcomings, said environmental epidemiologist Jaymie Meliker, the women included in the sample had relatively low levels of mercury overall. The study also failed to separate out the contribution of different species of fish, even though some varieties are known to contain more mercury than others.
“In essence, these researchers are saying that because they saw low levels of blood mercury in their population, mercury in fish is not a large problem,” said Meliker, of Stony Brook University in New York. But, he added, “there is strong evidence to the contrary from many studies in other populations.”
“It’s pretty clear that people who eat more fish, especially more high-mercury fish, have higher levels of mercury in them,” he said. “That’s been well established for at least 20 years.”
Mercury gets into the environment from coal-burning power plants, cement plants, steel production and other industrial sources. Once the environmental contaminant gets into oceans and rivers, according to the National Resources Defense Council, it accumulates in fish, including many that we eat.
In our bodies, mercury targets the nervous system and possibly the cardiovascular system, and developing fetuses are particularly vulnerable. Case studies have linked high levels of mercury exposure to infertility and miscarriage in pregnant women. Babies exposed in the womb can develop serious disabilities, including trouble with memory, attention and other thinking tasks.
Based on what we know so far, the United States Environmental Protection Agency has set safe mercury blood levels at 5.8 micrograms per liter. Still, there are many unknowns, including questions about the source of mercury in our bodies and the effects of long-term, low-dose exposures.