There is a global acceleration in the incidence of neurodevelopmental disorders. Numbers of children affected by an autism spectrum disorders (ASD) in the United States has reached 1 in 88 (1 in 56 boys), and even more have attention-deficit/hyperactivity disorder (ADHD). The cost of these disorders to the individual and society is enormous: ASD alone costs the United States a staggering 130 billion US dollars annually. Genetic causes cannot account for these increases. Surges in incidence must implicate environmental factors. Environmental chemicals interfering with thyroid hormone signaling ... More

There is a global acceleration in the incidence of neurodevelopmental disorders. Numbers of children affected by an autism spectrum disorders (ASD) in the United States has reached 1 in 88 (1 in 56 boys), and even more have attention-deficit/hyperactivity disorder (ADHD). The cost of these disorders to the individual and society is enormous: ASD alone costs the United States a staggering 130 billion US dollars annually. Genetic causes cannot account for these increases. Surges in incidence must implicate environmental factors. Environmental chemicals interfering with thyroid hormone signaling are potential culprits. This argument is substantiated by four facts. First, thyroid hormone is essential for brain growth; second, lack of thyroid hormone causes intellectual deficiency; third, many chemicals found in the environment have thyroid hormone–disrupting properties; and finally, many women enter pregnancy with insufficient iodine. Chemical pollution and iodine deficiency can also decrease the overall IQ of the population. Just a 5% decrease in overall IQ can have serious socioeconomic consequences, decreasing the numbers of gifted people and increasing those with IQs below 70. The author provides an historical overview of cases documenting environmental pollution causing IQ losses across populations, explains the physiology of thyroid hormone action, the importance of iodine and selenium for thyroid hormone signaling and brain development, why thyroid hormone is such a sensitive target of environmental pollution, and the role of gene × environment interactions in neurodevelopmental disorders. What can and is to be done by individuals, associations, and decision makers to staunch these epidemics is also detailed.