In a new study, higher maternal mercury levels were associated with more ADHD-related behaviors among children. However, fish consumption was protective against these behaviors.
In the past research has shown maternal levels of polychlorinated biphenyl (PCB) and p,p'-dichlorodiphenyl dichloroethylene were both associated with higher risks for ADHD babies being born to those mothers (Am J Epidemiol. 2010;171:593-601). There was a dose-response effect noted between concentrations of maternal PCBs and the risk for ADHD among children.
These same researchers now turn their attention to the association between maternal mercury exposure and the risk for ADHD among children. Because many individuals are exposed to mercury as a result of consuming fish, the authors examined maternal fish intake as a separate variable in their analysis.
Eating certain types of fish with even low levels of mercury while pregnant can increase the risk for ADHD in offspring, whereas consumption of several other types of fish during pregnancy may protect against the disorder, new research suggests.
A cohort study of almost 400 children showed that the risk for inattention and impulsivity at the age of 8 years was significantly associated with maternal mercury levels of at least 1 μg/g. In addition, as the mercury levels increased, so did risk.
However, when the mothers ate at least 2 servings of fish a week, the risk for ADHD symptoms decreased.
The study was published October 8 in the Archives of Pediatrics and Adolescent Medicine.
Dose-Dependent Effect
Between 1993 and 1998, 788 infants from Massachusetts were enrolled in this study, which was designed to assess a possible link between exposure to PCBs and neurodevelopment.
Soon after birth, hair samples were collected from the mothers and analyzed for mercury levels. The mothers also filled out a questionnaire regarding fish consumption during pregnancy.
At 8-year follow-up, 421 of these children were assessed for possible ADHD behaviors through the use of the Connors Rating Scale–Teachers, the Neurobehavioral Evaluation System 2 Continuous Performance Test, and 2 subscales of the Weschler Intelligence Scale for Children–Third Edition.
Results showed not only that mercury exposure associated with inattention and impulsivity/hyperactivity but also that the risk for these behaviors increased with maternal hair mercury levels.
The threshold for first association with ADHD symptoms appeared to be at least 1 μg/g or more of mercury.
In addition, these associations were more notable in boys than girls.
Protection of Fish
However, offspring of mothers who consumed at least 2 servings of fish a week, which is more than the current recommended amounts from the US Food and Drug Administration and the Environmental Protection Agency, had a decrease in ADHD-related behaviors, especially in impulsivity/hyperactivity (relative risk [RR], 0.4 vs 2 servings or fewer of fish per week).
Although the researchers did not assess which fish are worst and best to consume while pregnant, they noted in a release that previous studies have shown that shark, fresh tuna, and swordfish should be avoided by pregnant women, whereas fish such as haddock, salmon, and flounder are good because of their low levels of mercury and their nutritional value.
Most countries want to ban the use of mercury in dentistry (silver fillings). However, the United States refuses to be a part of this ban so far. I personally would suggest much of our mercury contamination is from dentistry practices. I would also suggest you go to a dentist that uses composites and not mercury amalgams (silver fillings).
