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Mercury in Seafood

U.S. Fish Advice May Expose Babies to Too Much Mercury

March 16, 2016

Mercury in Seafood: Findings

Since 2010 federal agencies have recommended that all adults eat eight to 12 ounces of fish and shellfish per week. In 2014 the FDA and EPA issued a draft recommendation that pregnant women eat the same amount.1 Currently, the average American adult eats 3.5 ounces of seafood a week.2

The recommendation to eat more seafood during pregnancy is primarily based on the benefits of two long chain omega-3 polyunsaturated fatty acids in fish and shellfish, referred to as DHA+EPA (docosahexaenoic acid and eicosapentaenoic acid). A diet rich in these omega-3s during pregnancy has been shown to boost babies’ brain development and improve their vision.3 Seafood is also a good source of high-quality protein and vitamins B and D, iodine and selenium.

The amounts of omega-3s and mercury in seafood vary widely depending on species. Women who increase the amount of fish in their diets without choosing the right species may not only fail to get the omega-3s they need but also risk ingesting too much mercury.

To investigate the implications of the federal seafood recommendations for pregnant women, we recruited online almost 300 women of childbearing age. We asked them to fill out a detailed questionnaire about the seafood they ate recently. From this information we chose 254 women in 40 states who ate as much as or slightly more than the FDA and EPA recommend. For comparison, we chose another 29 women who ate seafood rarely or not at all.

We collaborated with the University of Southern Denmark to measure the concentration of mercury in samples of the participants’ hair. The lab analyzed a small strand of hair taken closest to the scalp (two centimeters, about three-fourths of an inch) which reflects mercury ingested in the previous one to three months.

The hair of almost 30 percent of the women who reported eating seafood often had more mercury than EPA’s outdated exposure guideline of one part per million, a level that has now been associated with clear risks to a developing fetus. Nearly 60 percent of the women exceeded 0.58 part per million, the level Grandjean and other researchers say is a more protective upper limit for pregnant women.4 (A part per million is equal to one drop of water in 50 liters, or about 13 gallons, underscoring how tiny amounts of mercury are harmful.)

Mercury levels in the 254 women who frequently eat fish were six times higher than the median level found in a representative sample of all American women in 2004 by the National Health and Nutrition Examination Survey of the Centers for Disease Control and Prevention.5 They had an average of 11 times more mercury than the 29 women who eat seafood rarely, clearly indicating that the high mercury levels came from the fish rather than other sources.

Too many study participants have high mercury or low omega-3s


Source: EWG , from 2015 survey and tests of 254 U.S. women of childbearing age
Women with hair mercury levels +/- 1 ppm and estimated omega-3 intake +/- 250 mg of DHA+EPA per day.

Mercury levels in participants’ hair ranged from well below the EPA exposure guideline to 8.8 parts per million – almost nine times as high as the exposure guideline. Mercury levels were greater in those participants who ate higher mercury species frequently, suggesting that the type of fish women eat is more important than how frequently they eat fish and shellfish. (See Methodology Section in report PDF for detailed results.)

The government recommends that adults get an average of 250 milligrams of DHA+EPA daily.6 One study estimates that on average American women of childbearing age get only a third of the recommended amount of omega-3s,7 because most Americans don’t eat much fish and shellfish, and the most popular seafoods are very low in omega-3s.

Even though our study participants eat a lot of seafood, we estimate that six in 10 do not get the recommended amount of omega-3s to support an optimal pregnancy. The median omega-3 our participants got was 230 milligrams per day from seafood alone.

Just over one-fourth of our participants had both enough omega-3 intake and mercury levels below the EPA exposure guideline of 1 part per million. About one in six had higher levels of mercury and lower than optimal omega-3s, a particularly unhealthy combination.