Where Is All the Mercury Coming From?

Mercury levels in pregnant women come from other unidentified sources besides seafood

/ Author:  / Reviewed by: Robert Carlson, M.D Beth Bolt, RPh

(RxWiki News) One of the concerns pregnant women may have about their diet is the amount of seafood they can eat. Seafood contains mercury, a substance pregnant women should try to avoid.

Mercury exposure during pregnancy, at very high levels, can have negative effects on the developing brain of an unborn baby.

Yet a recent study found that seafood only accounts for a small portion of the possible sources of mercury a pregnant woman might be exposed to.

In fact, less than one-tenth of the mercury a woman might have in her body appears to come from seafood.

The remaining sources are in a handful of other foods, but most of the mercury sources are unclear.

"Discuss your diet with your OB/GYN."

The study, led by Jean Golding, of the Centre for Child and Adolescent Health at the University of Bristol in the United Kingdom, tried to determine all the different sources where pregnant women may be exposed to mercury.

One place women are exposed to mercury is through eating seafood. The researchers used extensive questionnaires and blood samples to learn other sources.

The researchers collected blood samples from 4,484 women enrolled in a long-term study of parents and children in England.

Then the women filled out lengthy questionnaires regarding their diet and their social and demographic characteristics.

The researchers estimated the extent to which 103 different foods or drinks contributed to mercury exposure in these women.

They also considered how six different social and demographic characteristics of the women contributed to their mercury exposure.

Overall, the researchers found that a woman's diet accounted for 20 percent of the differences in how much mercury was identified in the women's blood samples.

Within this 20 percent, the researchers identified that the amount of seafood the women ate accounted for just under half (44 percent) of the differences in their mercury blood levels.

In other words, the amount of seafood women ate (white fish, oily fish and shellfish) comprised about half of the dietary choices that might influence how much mercury her body got through food.

Other diet choices linked to a higher amount of mercury in women's blood included wine and herbal teas.

Meanwhile, eating more white bread, meat pies and pastries, and french fries was linked to lower levels of mercury in women's blood samples.

But food in general only accounted for one-fifth of the total mercury exposure that a pregnant woman might have or not have.

"Although seafood is a source of dietary mercury, seafood appeared to explain a relatively small proportion of the variation in total blood mercury in our UK study population," the researchers wrote.

"Although we confirmed that seafood was a major dietary contributor to blood mercury levels in our study population, estimated intakes of the three seafood items evaluated in our study (white fish, oily fish, and shellfish) accounted for only 8.75 percent of the estimated variation in log-transformed blood mercury concentrations," they wrote.

They also noted the major question that their study brings up: "Where is the rest of the blood mercury coming from?"

"The dangers of mercury exposure to a developing fetus are well documented," said Sarah Wagner, MD, obstetrician and gynecologist at Loyola Outpatient Center in Maywood and Loyola Center for Health at Oakbrook Terrace. "Obstetrics providers typically address only dietary exposures to mercury, and usually this discussion centers on seafood."

According to Dr. Wagner, "As we learn more about other potential exposures to mercury, this will allow us to go further to protect our patients. Patients should hold a detailed discussion about their diet and lifestyle with their obstetrics provider."

The study was published in the October issue of Environmental Health Perspectives. The authors declared no conflicts of interest.

The research was funded by the UK Medical Research Council, the Wellcome Trust, the University of Bristol, the US Centers for Disease Control and Prevention, the National Oceanic and Atmospheric Administration (NOAA) and the National Institute on Alcohol Abuse and Alcoholism.

Review Date: 
October 23, 2013
Last Updated:
November 4, 2013