Mercury Exposure In The Womb May Cause ADHD
December 9, 2012 by Robert Wascher
Filed under A Cancer Prevention Guide for the Human Race, ADHD, Attentiveness, Fish, Lead, Mercury, Mercury and Fish, Mercury in the Environement, Pregnancy, Weekly Health Update, attention deficit hyperactivity disorder, health, tobacco
Attention deficit/hyperactivity disorder (ADHD) in children may result from maternal exposure to mercury during pregnancy.
MERCURY EXPOSURE IN THE WOMB MAY CAUSE ADHD
Over the past 10 years, there has been a significant increase in the number of children diagnosed with attention deficit/hyperactivity disorder (ADHD). While the reasons behind this rising number of ADHD diagnoses continue to be debated, there is emerging clinical research data suggesting that maternal exposure to specific environmental toxins during pregnancy may significantly increase the incidence of ADHD among the children of these exposed mothers.
Previous studies have linked prenatal (“before birth”) exposure to lead, tobacco and mercury with a higher incidence of ADHD, but these studies have suffered from a significant limitation, in that they have relied upon surrogate measures of exposure to these toxins rather than direct, quantitative measures of exposure. Now, a newly published clinical study in the Archives of Pediatrics & Adolescent Medicine has overcome the limitations of previous studies, and strongly suggests that prenatal exposure to mercury increases the risk of ADHD.
There are multiple sources of potential mercury exposure in the environment around us. Indeed, more than half of all of the mercury introduced into the environment comes from manmade sources, including coal-fired power plants, steel plants, cement plants, mining operations, waste processing plants, battery manufacturing plants, and fluorescent bulb manufacturing plants, among other industrial sources. (Almost half of the mercury in the environment actually comes from naturally-occurring processes including, of all things, volcanic eruptions.) Once released into the environment, mercury then becomes concentrated, or “bio-amplified,” within the plants and animals that we eat, as well as in the water that we drink and the air that we breathe. Once ingested, mercury is a known toxin, with adverse effects on the nervous system (including the brain), lungs, kidneys, and other vital organs. As is the case with many environmental toxins, mercury is especially toxic to the unborn fetus, infants, and small children.
In this innovative new study, two groups of children were evaluated. In the first group (421 children), hair samples collected from the mothers of these children at around the time of their birth were analyzed for mercury content. In the second group (515 children), maternal hair samples were not available for testing, but maternal fish consumption (the most common source of mercury exposure) during pregnancy was evaluated, and this information was used to assess the impact of maternal fish intake on ADHD incidence in this second group of children.
The findings of this study were quite surprising.
The most important finding of this study was that increasing levels of mercury in the hair of mothers were significantly associated with a greater number of ADHD-related behaviors among their children. In particular, impulsive and hyperactive behaviors were 70 percent more common among the children of mothers with hair mercury levels at or above 1 microgram per gram of hair, and attention-deficit (“inattentiveness”) behaviors were 40 percent more common among these same children. Another interesting observation was that the association between maternal hair mercury levels and ADHD symptoms was identified primarily in boys, and was not commonly seen in girls.
Given that the single greatest source of mercury ingestion for most of us is fish consumption, one would expect that higher levels of maternal fish consumption would be associated with an increased risk of ADHD if, indeed, prenatal mercury exposure can lead to ADHD. However, this study actually found the opposite association between maternal fish intake during pregnancy and the risk of ADHD. In this study, maternal fish consumption of more than 2 servings for week during pregnancy was actually associated with a lower incidence of ADHD among the children of these mothers, including a 60 percent lower incidence of impulsive and hyperactive behaviors.
Mercury is a known nerve poison (neurotoxin), and there is data suggesting that the prefrontal cortex of the developing fetal brain is especially sensitive to the effects of even low levels of mercury and other environmental neurotoxins. As the prefrontal cortex (the “executive center” of the brain) is the area of the brain that exerts the greatest control on voluntary behavior, it is entirely reasonable to think that damage to this part of the brain could result in the inattentive and hyperactive behaviors that are the hallmarks of ADHD.
Based upon this study’s findings, it appears that maternal exposure to even relatively low levels of mercury (based upon maternal hair mercury content) during pregnancy may significantly increase the risk of ADHD-related behaviors in affected children. At the same time, the finding of the more subjective half of this study, which assessed maternal fish intake during pregnancy as a risk factor for ADHD-related behaviors, is rather counterintuitive, as fish consumption is thought to be the greatest source of mercury exposure for most humans. If, as this study suggests, increased maternal fish consumption during pregnancy is actually protective against ADHD-related behaviors, then environmental sources of mercury exposure other than fish must be involved in mercury-associated ADHD symptoms.
In my view, the findings of this study are very important, and, as an accompanying editorial notes, short of intentionally exposing children to mercury contamination for the sake of research, the hair analysis utilized in this study is as close as we are going to get to a “perfect” study of prenatal mercury exposure as a risk factor for ADHD.
Fortunately, there is an increasing awareness by public health experts regarding the potentially adverse health effects of environmental mercury. However, the findings of this study suggest that more must still be done to reduce mercury levels in the food that we eat, the water that we drink, and the air that we breathe.
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