A prospective study of prenatal mercury exposure from maternal dental amalgams and autism severity

By David A. Geier, Janet K. Kernand and Mark R. Geier

Introduction

The practice of using amalgams (which generally contain 50% mercury) in dentistry has existed for over 150 years. As of mid-2008, the US Food and Drug Administration (FDA) has declined to classify the medical-device safety of amalgams used in dentistry. The American Dental Association maintains that the mercury in amalgam is safe and that the mercury does not leak (Edlich et al. 2007).

Yet, the research evidence suggests that there is significant amount of elemental leaching and mercury vapor release from amalgams (Cohen and Penugonda 2001) and that this liberated mercury is absorbed by several body tissues (Mutter et al. 2004, Edlich et al. 2007). As a result, dental amalgams are a significant source of mercury body burden, as studies in animals and humans show (Mutter et al. 2007). For example, Guzzi and coworkers (2006) found that, on autopsy, total mercury levels were significantly higher in subjects with a greater number of amalgam surfaces (>12) compared with those who had fewer (0–3), in all types of tissue. These authors also reported that the greater the number of amalgams, the greater the likelihood that mercury would be found in the brain. In regard to amalgam bearers, other investigators have reported an approximate 2- to 5-fold increase of the mercury level in blood and urine as well as a 2- to 12-fold increase of the mercury concentration in several body tissues (Mutter et al. 2007). Also, mercury from maternal amalgam fillings leads to a significant increase of mercury concentration in the tissues and the hair of fetuses and newborn children. Furthermore, placental, fetal, and infant mercury body burden correlates with the numbers of amalgam fillings of the mothers (Mutter et al. 2007, Palkovicova et al. 2008). Finally, mercury levels in amniotic fluid and breast milk correlate significantly with the number of maternal dental amalgam fillings (Mutter et al. 2007).

The overall importance of dental amalgams, particularly maternal dental amalgams, significantly contributing to fetal and early infant mercury body-burden stems from the fact that recent studies have postulated that mercury exposure can cause immune, sensory, neurological, motor, and behavioral dysfunctions similar to traits defining or associated with autism spectrum disorders (ASDs), and that these similarities extend to neuroanatomy, neurotransmitters, and biochemistry (Mutter et al. 2005, Kern and Jones 2006, Maya and Luna 2006, Austin 2008, Geier et al. 2008b). In addi­tion, investigators from the US National Institute of Environmental Health Sciences (1999) and the National Institute for Occupation Safety and Health of the Centers for Disease Control and Prevention (Nelson 1991) have described a role for mercury exposure in the pathogenesis of autism. Mercury poisoning has also sometimes been presumptively diagnosed as autism of unknown etiology until mercury poisoning has been established (Chrysochoou et al. 2003) and other investigators have reported on a case-series of patients diag­nosed with mercury-induced ASDs (Geier and Geier 2007a). Further, Faustman and others (2000) reporting on the effects of mercury on neuronal development stated: “(…) mercury exposure altered cell number and cell division; these impacts have been postulated as modes of action for the observed adverse effects in neu­ronal development. The potential implications of such observations are evident when evaluated in context with research showing that altered cell proliferation and focal neuropathologic effects have been linked with specific neurobehavioral deficits (e.g., autism).” Finally, the Collaborative on Health and the Environment’s Learning and Developmental Disabilities (2008) recently published a consensus statement reporting that there is no doubt mercury exposure may produce ASDs.

Based upon the foregoing, it was hypothesized that mercury exposure from maternal dental amalgams during pregnancy may significantly impact the severity of ASD diagnoses. In order to evaluate this hypothesis, the present prospective, blinded study was designed to examine the relationship between mercury exposure from maternal dental amalgams during pregnancy and the severity of subjects diagnosed with an ASD. Further, the purpose of the analysis was to determine if there were a threshold number of maternal dental amalgams during pregnancy above which there was an increase in the severity of subjects diagnosed with an ASD.

CONCLUSIONS
The present study is the first prospective, blinded epidemiological study to evaluate the relationship between mercury exposure from maternal dental amalgams during pregnancy and its relationship with the severity of diagnosed ASDs. This study helps to demonstrate that elevated mercury exposure from maternal dental amalgams during pregnancy is associated with an elevated risk of being diagnosed with autism (severe clinical symptoms), in comparison to an ASD (mild clinical symptoms), and that the risk of increasing autism severity became apparent at the threshold of 6 or more maternal dental amalgams during pregnancy. The observations made in the present study are consistent with recently emerging evidence showing that there is a significant relationship between mercury exposure, particularly in the fetal and early infant temporal periods, and the subsequent risk of patients being diagnosed on the autism spectrum. Evidence from the present study, combined with other published research, suggests that policies on the use of dental amalgams should carefully consider the issue of mercury exposure in women before and during the child-bearing age and the possibility of subsequent fetal exposure and adverse outcomes. Future studies should be conducted to further evaluate the critical relationship between mercury exposure from dental amalgams during fetal and early infant temporal periods and the subsequent risk of these children developing neurodevelopmental disorders.

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First published 2009

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