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How Heavy Metals Affect Neurotransmitters Production and Balance

by Manuela Malaguti Boyle and Geoff Beaty(more info)

listed in environmental, originally published in issue 174 - September 2010

The human brain forms and develops over a long period compared to other organs, with neuron proliferation and migration continuing in the postnatal period. The blood-brain barrier is not fully developed until the middle of the first year of life. Similarly there is postnatal activity in the development of neuronal receptors and transmitter systems, as well as in the production of myelin. The foetus has been found to get significant exposure to toxic substances through maternal blood and across the placenta, with foetal levels of toxic metals often being higher than that of maternal blood.[3,6] Likewise infants have been found to get significant exposure to toxics, such as mercury and organochlorine compounds that their mother is exposed to, through breast-feeding.

A recent report by the National Research Council found that 50% of all pregnancies in the US are now resulting
in prenatal or postnatal mortality, significant birth
defects, developmental neurological problems, or otherwise chronically unhealthy babies.

The incidence of neurotoxic or immune reactive conditions such as autism, schizophrenia, ADD, dyslexia and learning disabilities have been increasing rapidly in recent years. A recent report by the National Research Council found that 50% of all pregnancies in the US are now resulting in prenatal or postnatal mortality, significant birth defects, developmental neurological problems, or otherwise chronically unhealthy babies.[6] Not all children are equally affected by a given level of toxic exposures, and susceptibility factors such as immune reactivity, genetic factors affecting ability to excrete toxic metals, and other toxic exposures have major influences on toxicity effects.

Studies and clinical experience at treatment clinics have found consistently that gastrointestinal, immunological and metabolic problems are found in children with ADHD, that are related to prenatal and neonatal exposure to toxic substances with much of these being related to vaccinations.[3,7,9] In fact, lower GI dysfunction, enzyme deficiencies and impairments of hepatic detoxification pathways are very common. Many ADHD/autism patients have 'leaky gut' syndrome, and inability to digest wheat, gluten and milk casein, resulting in neurotoxic substances being dumped in the blood with significant adverse behavioural impacts.[10]
According to the US Census Bureau, exposure to toxic chemicals or environmental factors appear to be a factor in at least 28 percent of the 4 million US children born each year, with at least 1 in 6 having one of the neurological conditions previously listed. It is estimated that over 3 million of these are related to lead or mercury toxicity, with approximately 25% of US kids getting mercury exposure at dangerous levels. Evidence indicates that over 60,000 children are born each year with neurodevelopmental impairment due to methyl mercury, with even higher levels of exposure and impairment from two other sources, vaccines and mother's amalgam dental fillings.[2,3]
The toxic metals lead, mercury, and arsenic are the top 3 toxins having the most adverse health effects on the public based on toxicity; current exposure levels with cadmium, chromium and nickel also highly listed. According to the American Academy of Child and Adolescent Psychiatry, an estimated one out of every 6 children in the US have blood levels of lead in the toxic range, and studies estimate that over 12 million children suffer from learning, developmental, and behavioural disabilities including ADD, autism, schizophrenia, and mental retardation.[4,8] Large numbers of people have been found to have allergic conditions and immune reactive autoimmune conditions due to the toxic metals, especially inorganic mercury and nickel. These metals have also been found to diminish the cellular ATP energy function and be related to chronic fatigue.
The level of exposure in most infants to mercury thimerosal has been found to be many times higher than the federal limits for mercury exposure. The largest increase in neurological problems has been in infants, with an increase in autism cases to over 500,000, an over 500% increase to a level of almost 1 per 300 infants in the last decade, making it the 3rd most common chronic childhood condition, along with similar increases in ADD.[7,11] According to the American Academy of Pediatrics, between 4 to 12 % of all school age children are affected by ADHD and a similar number have some degree of dyslexia. However large surveys of elementary level student records finds much higher levels - with over 20% of elementary school boys in some areas being treated for ADD. Similar levels of children have been found to have mood or anxiety disorders.[6,7] Studies have found that long term use of stimulant drugs commonly are not effective in the long run, and causes significant adverse neurological and health effects. There are more effective options available to deal with such conditions without such adverse effects, including dealing with the underlying causes and diet, exercise, and supplement options that deal with underlying deficiencies.

The heavy metals (lead, mercury, cadmium, nickel) tend to concentrate in the air and in the food chain along with other toxic metals such as aluminium, facilitating metal poisoning which is the most widespread environmental disorder in the US.[5] Mercury and cadmium from combustion emissions are also accumulating in coastal estuaries and inland water body sediments, and are widespread in shellfish and other organisms. Mercury and cadmium are extremely toxic at very low levels and have serious impacts on the organisms in water bodies that accumulate them. These heavy metals have also been found to be endocrine system-disrupting chemicals and have been found to be having effects on the endocrine and reproductive systems of fish, animals, and people, similar to the reproductive and developmental effects of organochlorine chemicals.[1]

Studies have found that heavy metals such as mercury, cadmium, lead, aluminium, and tin affect chemical synaptic transmission in the brain and the peripheral and central nervous system.[9,2,4] They also have been found to disrupt brain and cellular calcium levels that significantly affect many body functions, such as cognitive development and degenerative CNS diseases, which results in depressed levels of serotonin, norepinephrine, and acetylcholine; cellular calcium-sodium ATP pump processes affecting cellular nutrition and energy production processes and causing skeletal osteodystery . Toxic metals have also been found to affect cellular transfer and levels of other important minerals and nutrients that have significant neurological and health effects such as magnesium, lithium, zinc, iron, Vitamins B6 and B12[1, 3,4] Based on thousands of hair tests, at least 20 % of Americans are deficient in magnesium and lithium, with zinc and iron deficiencies also common. The resulting deficiency of such essential nutrients has been shown to increase toxic metal neurological damage. Cerebrospinal magnesium was found to be significantly lower in both depression and adjustment disorder and in those who have attempted suicide.[6,7]

Much of the developmental effects of mercury and other toxic metals are due to prenatal and neonatal exposures damage to the developing endocrine system. A recent study found that prenatal Hg exposure is correlated with lower scores in neurodevelopmental screening, but more so in the linguistic pathway. Prenatal and neonatal toxic metal exposure to mercury, lead, arsenic, cadmium, nickel, and aluminium have been documented in medical publications and medical texts to cause common and widespread neurological and psychological effects, including depression, anxiety, obsessive compulsive disorders, social deficits, other mood disorders, schizophrenia, anorexia, cognitive impairments, ADHD, autism, seizures, etc. Children with autism had significantly higher levels of mercury in baby teeth, but similar levels of lead and similar levels of zinc.[2, 5] Children with autism also had significantly higher usage of oral antibiotics during their first 12 months of life. Baby teeth are a good measure of cumulative exposure to toxic metals during foetal development and early infancy.

Studies have also found heavy metals to deplete glutathione and bind to protein-bound sulfhydryl groups, resulting in inhibiting SH-containing enzymes and production of reactive oxygen species such as superoxide ion, hydrogen peroxide, and hydroxyl radical. In addition, toxic metals exert part of their toxic effects by replacing essential metals such as zinc at their sites in enzymes. An example of this is mercury's disabling of the metallothionein protein, which is necessary for the transport and detoxification of metals. Another large study found a high percentage of autistic and ADD children are especially susceptible to metals due to the improper functioning of their metallothionein detoxification process, and that with proper treatment most recover.[4, 11]

Mercury has also been found to play a part in neuronal problems through blockage of the P-450 enzymatic process. Mercury induced reactive oxygen species and lipid peroxidation has been found to be a major factor in mercury's neurotoxicity, along with leading to decreased levels of glutathione peroxidation and superoxide dismutase. This research has been found to be significant because it establishes a direct connection in neurological and immune damage caused by the heavy metals, including damage to mitochondria and DNA, as well as chronic autoimmune conditions and diseases. Turmeric (curcumin) has strong antioxidant effects and has been shown to counteract lipid peroxidation and toxicity effects of metals and to reduce the toxic effects of metals such as copper, lead and cadmium.

The effects on DNA are a factor in several of the toxic metals such as arsenic, beryllium, cadmium, chromium, and nickel being known carcinogens, but chronic exposure to other toxic metals such as mercury are also known to promote cancer through their DNA effects and suppression of the immune system.

Although vaccinations appear to be the largest source of mercury in infants, mercury has been found to be transmitted from the mother to the foetus through the placenta and accumulate in the foetus to higher levels than in the mother's blood. Breast milk of women who have amalgam fillings is the second largest source of mercury in infants and young children, but eating a lot of fish has also been found to be a significant source of methyl mercury.[3] Milk increases the bioavailability and retention of mercury by as much as double, and mercury is often stored in breast milk and the foetus at much higher levels than that in the mother's tissues. Mercury is transferred mainly by binding to casein.[1,8,10]

High lead, copper, manganese, or mercury levels have been found to be associated with attention deficit hyperactivity disorder(ADHD), memory deficits, impulsivity, anger, aggression, inability to inhibit inappropriate responding, juvenile delinquency, and criminality. Mercury has been found to be a factor in anger, aggressive behaviour, depression, obsessive compulsive behaviour (OCD), ADD, autism, schizophrenia, suicidal behaviours, learning disabilities, anxiety , mood disorders, and memory problems. It has been found that excess levels of copper can cause violent behaviour in children.[2,9] A study that investigated the effects of zinc and copper on the behaviour of schizophrenic patients by comparing blood zinc and copper levels in criminal and non-criminal schizophrenic patients found criminal subjects have significantly lower zinc levels and higher copper levels than non-criminal subjects.


1. ATSDR/EPA Priority List for 2003: Top 20 Hazardous Substances, Agency for Toxic Substances and Disease Registry U.S. Department of Health and Human Services,  ; United States Environmental Protection Agency, Office of Water, June 2003, The National Listing of Fish and Wildlife Advisories: Summary of 2002 Data, EPA-823-F-00-20,  ; Toxicological Effects of Methylmercury pp. 304-332. 2000. Risk Characterization and Public Health Implications, Nat'l Academy Press 2000.  ; and (d) U.S. Centers for Disease Control, Mar 2001, Blood and Hair Mercury Levels in Young Children and Women of Childbearing Age - United States, 1999.  ; and U.S. CDC, Second National Report on Human Exposure to Environmental Chemicals,
2. Assessment, Cincinnati, Ohio webpage EPA spokesman, US. News & World Report, "Kids at Risk", 6-19-2000; & U.S. EPA, Region I, 2001,  
3. J.O. Nriagu, Global Metal Pollution- Poisoning the Biosphere, Environment, Vol. 32, No. 7, Sept. 1990; and Shukla GS, Singhal RL. The present status of biological effects of toxic metals in the environment: lead, cadmium, and manganese. Can J Physiol Pharmacol. 62(8):1015-31. Aug 1984; Science News, Nov 6 P327. 1986.
4. Agency for Toxic Substances and Disease Registry, U.S. Public Health Service. Toxicological Profile for Mercury. March 1999. and Media Advisory, New MRLs for toxic substances, MRL: elemental mercury vapor/ inhalation/chronic & MRL: methyl mercury/oral/acute. Jan 2003.  
5. Goyer RA, National Institute of Environmental Health Sciences. Toxic and essential metal interactions. Annu Rev Nutr 17:37-50. 1997. and Nutrition and metal toxicity. Am J Clin Nutr 61 (Suppl 3): 646S-650S. 1995. and Goyer RA et al, Environmental Risk Factors for Osteoporosis, Environmental Health Perspectives, 102(4): 390-394; & Michael Wentzel, UR links childhood lead to osteoporosis. Democrat and Chronicle. Feb. 25 1994.
6. Marlowe M, Cossairt A, Moon C. Errera J. Main and Interactive Effects of Metallic Toxins on Classroom Behavior, Journal of Abnormal Child Psychology 13(2): 185-98. 1985.
7. Pihl RO, Parkes M. Hair element content in learning disabled children. Science 198(4313):204-6. 1977.
8. Moon C, Marlowe M Stellem J, Errera J. Main and Interactive Effects of Metallic Pollutants on Cognitive Functioning, Journal of Learning Disabilities 18(4):217-221. 1985.
9. Lewis M, Worobey J, Ramsay DS, McCormack MK. Prenatal exposure to heavy metals: effect on childhood cognitive skills and health status. Pediatrics 89(6 Pt 1):1010-15. 1992.
10. Capel ID, Pinnock MH, Dorrell HM, Williams DC, Grant EC. Comparison of concentrations of some trace, bulk, and toxic metals in the hair of normal and dyslexic children. Clin Chem Jun; 27(6):879-81. 1981.
11. Marlowe M, Errera J, Jacobs J. Increased lead and cadmium burdens among mentally retarded children and children with borderline intelligence. Am J Ment Defic Mar;87(5):477-83. 1983 and Journal of Special Education 16:87-99. 1982.


  1. Lajos Lakatos MD, DSc said..

    I don't find my comment I was writing yesterday here.
    Best wishes,
    L. Lakatos

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About Manuela Malaguti Boyle and Geoff Beaty

Manuela Malaguti Boyle ND is a Naturopath and Clinical Nutritionist, trained in Australia. Her area of expertise is nutritional therapy as a viable treatment for mental illness. She continuously researches how nutrition impacts the nervous system function and brain cognition. Manuela firmly believe that 'junk food gives rise to junk thoughts' and she seek to help patients improve their state of mind and coping abilities. Nutritional interventions safely complement standard drug treatments. Manuela's articles have appeared in several publications both in United Kingdom and Australia. Manuela may be contacted on  

Geoff Beaty DN MNHAA is a Medical Herbalist trained by a third generation Herbalist and Naturopath in Perth, Western Australia. He has broad experience over 20 years and his highly successful reputation is built on his excellent ability to diagnose and treat the underlying causes of disease and thus get lasting results. Geoff is a well renowned Kinesiologist and Orthodynamics and Bowen technique specialist. He may be contacted on


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