It’s known that lead causes cognitive deficits, but how?

Ever since dangerously high lead levels in the drinking water in Flint, Michigan, made national headlines, there’s been heightened interest in the risk of this toxin — not only in water, but also in the much larger problem in Pittsburgh of lead exposure in old housing stock and neighbourhoods near industrial sites. But what exactly does lead do to the body, and who is most at risk? Lead causes a multitude of cognitive deficits, from attention problems and learning disorders to disruptive behaviours, impulsivity and increased aggression. Lead is most detrimental to children because their brains are still developing — in fact they absorb 4 to 5 times as much ingested lead as adults from a given source, according to the World Health Organization. There is no safe level of lead, according to the Centres for Disease Control and Prevention, and damage is irreversible. Not all is understood on its impact, but one thing is clear — the best treatment is prevention and abatement. “When a child has already been chronically lead poisoned, they often present with a form of neurodevelopmental disability,” said Scott Faber, the director of developmental paediatrics at The Children’s Institute. “We are much better off as a culture if we do proactive work with community and governmental stakeholders to upgrade our infrastructure and eliminate lead in the older homes and water systems.” Dr. Faber said lead burdens the metalloprotein detoxification system, a system meant to naturally purify the body of heavy metals. The system, which is reliant on zinc, is already stressed in cities such as Pittsburgh, which provides high exposure to heavy metals. An overworked system can lead to the body being depleted of zinc levels, which are important for brain functioning. In addition, lead poisoning can cause calcium deficiency. The elevated blood lead levels and low zinc levels are also associated with iron deficiency, he said. When lead enters the body, it mimics the calcium ion, according to Anthony Pizon, a toxicologist at the Pittsburgh Poison Centre. About 90 percent of lead is stored in the bones, while the other 10 percent takes advantage of its similarity in shape and charge to the calcium ion and uses the body’s natural pathways to reach the brain. Once inside the brain, the calcium ion (or in this case, lead) plays a role in the release of neurotransmitters, the electrical connections that allow communication within the brain and body. Dr. Pizon said it is “theorised that lead causes inappropriate release of neurotransmitters.” “Your body intentionally prunes or cuts back some of the connections to make it more efficient,” Dr. Pizon said. “In a child’s brain, this lead behaving like calcium causes a lot of neurotransmitters to fire so your brain doesn’t know what to prune.” Researchers say the lead may cause both too much pruning and too little pruning, which Dr. Pizon said would be “like a short circuit. Too much wiring isn’t always better than too little.” While the lead is disturbing the neurotransmitters, it is also at work destroying the myelin sheath, the protective coating around the pathways that neurotransmitters travel, which slows the connections down. The destruction of the myelin sheath causes problems with connections in the brain as well as connections from the brain to the rest of the body, slowing some movements and impulses, Dr. Pizon said. In a 2008 study of adults with childhood lead exposure, Kim Cecil, a researcher at the Cincinnati Children’s Hospital Medical Centre, and her colleagues found that participants had decreased brain volume in the regions of the brain responsible for executive functions, such as decision making, aggressiveness and impulsivity. More men than women had greater deficits in grey matter, which she called the “action centres,” meaning they are involved in muscle control and sensory perception. On the other hand, women had greater deficits in white matter, which makes up the “highway system that connects” the brain to the rest of the body. With so many different impacts on the brain, it is not surprising that lead poisoning manifests itself differently in each child. Dr. Faber said the reasons for symptoms are usually a mixture of genetic and environmental factors. “Whenever there’s exposure to any heavy metal in a family, the person that detoxifies the worst is the canary in the coal mine,” he said. “That person is usually a child, whose blood or urine levels of the heavy metal will be elevated, signalling the need to check other family members for significant exposure to the same heavy metal.” Gary Swanson, a child and adolescent psychiatrist with the Allegheny Health Network, said it is difficult to tell if a child’s cognitive deficits are a result of lead poisoning or a developmental disability that would have already been a problem. Regardless of cause, he treats developmental disabilities from lead poisoning with medicines and behavioural therapies used for treatment of other disabilities. With the therapies, Dr. Swanson said it is possible that the brain can rebuild some of the connections that were lost. “You’re hoping the brain will fix itself, hoping the brain will bounce back,” he said. However, because the treatments were designed for a different problem, he said he cannot expect the same high response rate that he sees in children with similar disabilities caused by different factors. Behavioural intervention and psychiatric medications are used only for children who have high blood lead levels and also display symptoms of cognitive deficits. For those who don’t, treatment procedures depend on how high their blood lead levels are. Blood lead levels of 5 micrograms per decilitre are used as a reference point for an unusually high level. Doctors might treat children with a series of micronutrients, including zinc, iron and a probiotic to help the gut bacteria better absorb lead so it can be eliminated from the body. Close monitoring is important. For those children with blood lead levels above 45 micrograms per decilitre, some doctors consider chelation therapy. Generally, Basil Zitelli, chief of the Paul C. Gaffney Diagnostic Service at Children’s Hospital of Pittsburgh of UPMC, said he will use an oral drug called succimer that acts as a “metabolic sponge,” binding to the lead so it doesn’t travel from the blood to the bones or the brain and is removed from the body by the kidneys. The drug is taken usually for 14 days and can require several rounds. Dr. Zitelli said he continues to prescribe the drug until he is sure the child is removed from the source of lead and the blood lead levels continuously fall. “If we don’t have to use the drug, I would prefer not to. First and foremost is to get rid of the source [fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][of lead],” he said. “You should not have lead in your body. Period.”

Pittsburgh Post Gazette, 19 July ;http://www.pittsburghlive.com ;[/fusion_builder_column][/fusion_builder_row][/fusion_builder_container]