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Autism, also known as autism spectrum disorder, is a broad range of conditions that affect communication and behavior, usually appearing by age 2. The Centers for Disease Control and Prevention (CDC) reports that autism affects 1 in 36 children.

Introduction

Photo of a child with autism

Autism

Autism, also known as autism spectrum disorder, is a broad range of conditions that affect communication and behavior, usually appearing by age 2. The Centers for Disease Control and Prevention (CDC) reports that autism affects 1 in 36 children. 1 This data reflects in part an increased ability to recognize and diagnose characteristics of autism spectrum disorder earlier in a child's life.

People with autism may have difficulty with communication and social interaction; restricted interests and repetitive behaviors; that may result in challenges at school, work, and other areas of life.
 

What Causes Autism?

Studies indicate the rate of autism is rising, but causes are not well-understood. Scientists have found rare gene changes, or mutations, as well as small common genetic variations in people with autism, implying a genetic component. Some factors that indicate genetic influences on the development and diagnosis with autism include:

  • A twin or sibling with autism
  • Older parents
  • Certain genetic conditions, such as Down, fragile X, and Rett syndromes

A growing area of research focuses on the interaction of genetic and environmental factors. For example, the impact of exposure to a harmful contaminant may be influenced by a pregnant person’s or fetus’ genetic background.. No link has been found between autism and vaccines, including those containing thimerosal, a mercury-based compound.

What Environmental Factors May Be Associated With Autism?

Progress has been made toward understanding different environmental contributors, and the clearest evidence involves events before and during birth, such as:

  • Advanced parental age at time of conception
  • Prenatal exposure to air pollution or certain pesticides
  • Maternal obesity, diabetes, or immune system disorders
  • Extreme prematurity or very low birth weight
  • Any birth difficulty leading to periods of oxygen deprivation to the baby’s brain

But these factors alone are unlikely to cause autism. Rather, they appear to increase a child’s likelihood for developing autism when combined with genetic factors.

  1. CDC (U.S. Centers for Disease Control and Prevention) 2018. Data and Statistics on Autism Spectrum Disorder. [accessed 7 March 2019]. [Available CDC (U.S. Centers for Disease Control and Prevention) 2018. Data and Statistics on Autism Spectrum Disorder. [accessed 7 March 2019].]

What is NIEHS Doing?

For more than two decades, NIEHS has explored environmental contributions to autism, supporting collaborations in the U.S. and abroad through a dedicated extramural funding program. The first projects received funding in 2002. Some highlights from that research are described below.

Exploring biomarker based predictors of diagnosis - Researchers have developed tests that analyze patterns of environmental exposures in hair strand growth associated with autism diagnosis, using as little as one month of hair growth. Earlier diagnosis of autism, allows for earlier behavioral and social interventions, which studies show can dramatically improve outcomes for children on the spectrum.

Air pollution – Researchers found early-life exposure to air pollution may be a risk factor for autism.

  • Children of mothers living near a freeway, and traffic-related pollution, during the third trimester of pregnancy were twice as likely to develop ASD. A distance of 1,014 feet, or a little less than 3.5 football fields, was considered near a freeway.2
  • Children with a mutation in a gene called MET, combined with high levels of exposure to air pollution, may have increased risk.3

Prenatal conditions and maternal factors – Problems with a mother’s immune system, certain metabolic conditions, or inflammation during pregnancy may be linked with higher rates of autism diagnosis for her children.

  • Some mothers of autistic children have antibodies, or proteins in the body that fight infection, that may interfere with their children’s brain development, possibly leading to autism.4
  • Maternal diabetes or obesity are linked to increased likelihood of having a child with autism or other developmental disability.5
  • Fever during pregnancy was associated with increased autism in offspring.6

Metals, pesticides, and other contaminants – Prenatal and early childhood exposure to heavy metals, like mercury, lead, or arsenic; altered levels of essential metals like zinc or manganese; pesticides; and other contaminants cause concern.

  • For people in the Republic of Seychelles, fish consumption is high and a primary way they are exposed to mercury. But a study there found no association between this type of prenatal, dietary mercury exposure and autism.7
  • Researchers found that after adjusting for dietary and other mercury sources, children with autism had similar mercury levels in blood as those without.8
  • A study of twins used baby teeth to determine and compare levels of lead, manganese, and zinc in children with autism to their twin without the condition. Autistic children had lower levels of essential metals, manganese and zinc, but had higher levels of lead, a harmful metal during specific developmental time periods studied.9
  • Researchers further found that  zinc-copper cycles, which regulate metal metabolism in the body, are disrupted in ASD cases compared to their twins not diagnosed with ASD.10
  • Maternal exposure to the insecticide DDT during early pregnancy was associated with higher risk of autism in their children.11
  • Researchers are also studying contaminants such as Bisphenol A, phthalates, flame retardants, and polychlorinated biphenyls to see if they affect early brain development and possibly play a role in autism.

Nutrition – NIEHS-funded studies have found taking prenatal vitamins may help lower autism likelihood of autism diagnosis. Furthermore, research suggests taking vitamins and supplements might provide protective effects for those exposed to certain environmental contaminants during pregnancy.

  • Women were less likely to have a child with autism if they took a daily prenatal vitamin during the three months before and first month of pregnancy, compared to women not taking vitamins. This finding was more evident in women and children with genetic variants that made them more susceptible to developing autism.12
  • Folic acid is a source of the protective effects of prenatal vitamins. Women who took the daily recommended dosage during the first month of pregnancy had a reduced likelihood of having a child with autism.13
  • Pregnant mothers who used multivitamins, with or without additional iron or folic acid, were less likely to have a child with autism and intellectual disability.14
  • Folic acid intake during early pregnancy may reduce the impact on autism diagnosis of high exposure to air pollution15 , and pesticides during pregnancy.16
  • Maternal prenatal vitamin intake during the first month of pregnancy may also reduce ASD recurrence in siblings of children with ASD.17

Notable NIEHS-funded, epidemiology studies– NIEHS-funded scientists are working to better understand the environmental contributors to ASD through their continued work on the Childhood Autism Risk from Genetics and the Environment (CHARGE) study, the Markers of Autism Risk in Babies - Learning Early Signs (MARBLES) study, and The Early Autism Risk Longitudinal Investigation (EARLI) study.  

CHARGE, with more than 1,800 children enrolled, seeks to clarify the roles of genetics and environmental exposures in autism. Results indicate a variety of exposures may be associated with autism, including pesticides, air pollution, and maternal metabolic or immune conditions

MARBLES, with more than 400 mother-child pairs, is a unique study in that it obtains information about how exposures before, during, and after pregnancy may contribute to autism. Recent research has included work studying the effect that prenatal exposure to phthalates and prenatal vitamins may have on autism development.18

EARLI is another study that enrolled a large group of pregnant mothers of children with autism. The newborn child – the sibling to the child with ASD – was subsequently followed through three years of age to see if he or she was diagnosed with ASD. While the study enrollment has ceased, the investigators continue to use data and biospecimens from the study to  examine possible environmental risk factors for autism and possible links between genes and the environment, known as gene-environment interactions.

Federal Collaboration

Interagency Autism Coordinating Committee (IACC) – IAAC is a federal advisory committee that coordinates federal efforts and provides advice to the secretary of the U.S. Department of Health and Human Services on issues related to autism spectrum disorder. NIEHS partners with members of IACC to summarize advances in autism research and participate in strategic planning for research needs. The committee works closely with the public, to hear their concerns and recommendations for research.

  1. Volk HE, Hertz-Picciotto I, Delwiche L, Lurmann F, McConnell R. 2011. Residential proximity to freeways and autism in the CHARGE study. Environ Health Perspect 119(6):873-877. [Abstract Volk HE, Hertz-Picciotto I, Delwiche L, Lurmann F, McConnell R. 2011. Residential proximity to freeways and autism in the CHARGE study. Environ Health Perspect 119(6):873-877.]
  2. Volk HE, Kerin T, Lurmann F, Hertz-Picciotto I, McConnell R, Campbell DB. 2014. Autism spectrum disorder: interaction of air pollution with the MET receptor tyrosine kinase gene. Epidemiology 25(1):44-47. [Abstract Volk HE, Kerin T, Lurmann F, Hertz-Picciotto I, McConnell R, Campbell DB. 2014. Autism spectrum disorder: interaction of air pollution with the MET receptor tyrosine kinase gene. Epidemiology 25(1):44-47.]
  3. Jones KL, Van D Water J. 2018. Maternal autoantibody related autism: mechanisms and pathways. Mol Psychiatry. 24(2):252-265. [Abstract Jones KL, Van D Water J. 2018. Maternal autoantibody related autism: mechanisms and pathways. Mol Psychiatry. 24(2):252-265.]
  4. Krakowiak P, Walker CK, Bremer AA, Baker AS, Ozonoff S, Hansen RL, Hertz-Picciotto I. 2012. Maternal metabolic conditions and risk for autism and other neurodevelopmental disorders. Pediatrics 129(5):e1121-e1128. [Abstract Krakowiak P, Walker CK, Bremer AA, Baker AS, Ozonoff S, Hansen RL, Hertz-Picciotto I. 2012. Maternal metabolic conditions and risk for autism and other neurodevelopmental disorders. Pediatrics 129(5):e1121-e1128.]
  5. Brucato M, Ladd-Acosta C, Li M, Caruso D, Hong X, Kaczaniuk J, Stuart EA, Fallin MD, Wang X. 2017. Prenatal exposure to fever is associated with autism spectrum disorder in the Boston birth cohort. Autism Res 10(11):1878-1890. [Abstract Brucato M, Ladd-Acosta C, Li M, Caruso D, Hong X, Kaczaniuk J, Stuart EA, Fallin MD, Wang X. 2017. Prenatal exposure to fever is associated with autism spectrum disorder in the Boston birth cohort. Autism Res 10(11):1878-1890.]
  6. Van Wijngaarden E, Davidson PW, Smith TH, Evans K, Yost K, Love T, Thurston SW, Watson GE, Zareba G, Burns CM, Shamlaye CF, Myers GJ. 2013. Autism spectrum disorder phenotypes and prenatal exposure to methylmercury. Epidemiology 24(5):651-659. [Abstract Van Wijngaarden E, Davidson PW, Smith TH, Evans K, Yost K, Love T, Thurston SW, Watson GE, Zareba G, Burns CM, Shamlaye CF, Myers GJ. 2013. Autism spectrum disorder phenotypes and prenatal exposure to methylmercury. Epidemiology 24(5):651-659.]
  7. Hertz-Picciotto I, Green PG, Delwiche L, Hansen R, Walker C, Pessah IN. 2010. Blood mercury concentrations in CHARGE Study children with andwithout autism. Environ Health Perspect 118(1):161-166. [Abstract Hertz-Picciotto I, Green PG, Delwiche L, Hansen R, Walker C, Pessah IN. 2010. Blood mercury concentrations in CHARGE Study children with andwithout autism. Environ Health Perspect 118(1):161-166.]
  8. Arora M, Reichenberg A, Willfors C, Austin C, Gennings C, Berggren S, Lichtenstein P, Anckarsäter H, Tammimies K, Bölte S. 2017. Fetal and postnatal metal dysregulation in autism. Nat Commun 8:15493. [Abstract Arora M, Reichenberg A, Willfors C, Austin C, Gennings C, Berggren S, Lichtenstein P, Anckarsäter H, Tammimies K, Bölte S. 2017. Fetal and postnatal metal dysregulation in autism. Nat Commun 8:15493.]
  9. Curtin P, Austin C, Curtin A, Gennings C, Arora M, Tammimies K, Wilfors C, Berggre S, Siper P, Rai D, Meyering K, Kolevzon A, Mollon J, David AS, Lewis G, Zammit S, Heilbrun L, Palmer RF, Wright RO, Bölte S, Reichenberg A. 2018. Dynamical features in fetal and postnatal zinc-copper metabolic cycles predict the emergence of autism spectrum disorder. Sci Adv 30;4(5). [Abstract Curtin P, Austin C, Curtin A, Gennings C, Arora M, Tammimies K, Wilfors C, Berggre S, Siper P, Rai D, Meyering K, Kolevzon A, Mollon J, David AS, Lewis G, Zammit S, Heilbrun L, Palmer RF, Wright RO, Bölte S, Reichenberg A. 2018. Dynamical features in fetal and postnatal zinc-copper metabolic cycles predict the emergence of autism spectrum disorder. Sci Adv 30;4(5).]
  10. Brown AS, Cheslack-Postava K, Rantakokko P, Kiviranta H, Hinkka-Yli-Salomäki S, McKeague IW, Surcel HM, Sourander A. 2018. Association of Maternal Insecticide Levels With Autism in Offspring From a National Birth Cohort. Am J Psychiatry; doi: 10.1176/appi.ajp.2018.17101129. [Abstract Brown AS, Cheslack-Postava K, Rantakokko P, Kiviranta H, Hinkka-Yli-Salomäki S, McKeague IW, Surcel HM, Sourander A. 2018. Association of Maternal Insecticide Levels With Autism in Offspring From a National Birth Cohort. Am J Psychiatry; doi: 10.1176/appi.ajp.2018.17101129.]
  11. Schmidt RJ, Hansen RL, Hartiala J, Allayee H, Schmidt LC, Tancredi DJ, Tassone F, Hertz-Picciotto I. 2011. Prenatal vitamins, one-carbon metabolismgene variants, and risk for autism. Epidemiology 22(4):476-485. [Abstract Schmidt RJ, Hansen RL, Hartiala J, Allayee H, Schmidt LC, Tancredi DJ, Tassone F, Hertz-Picciotto I. 2011. Prenatal vitamins, one-carbon metabolismgene variants, and risk for autism. Epidemiology 22(4):476-485.]
  12. Schmidt RJ, Tancredi DJ, Ozonoff S, Hansen RL, Hartiala J, Allayee H, Schmidt LC, Tassone F, Hertz-Picciotto I. 2012. Maternal periconceptionalfolic acid intake and risk of autism spectrum disorders and developmental delay in the CHARGE (CHildhood Autism Risks from Genetics and Environment) case-control study. Am J Clin Nutr 96(1):80-89. [Abstract Schmidt RJ, Tancredi DJ, Ozonoff S, Hansen RL, Hartiala J, Allayee H, Schmidt LC, Tassone F, Hertz-Picciotto I. 2012. Maternal periconceptionalfolic acid intake and risk of autism spectrum disorders and developmental delay in the CHARGE (CHildhood Autism Risks from Genetics and Environment) case-control study. Am J Clin Nutr 96(1):80-89.]
  13. DeVilbiss EA, Magnusson C, Gardner RM, Rai D, Newschaffer CJ, Lyall K, Dalman D, Lee BK. 2017. Antenatal nutritional supplementation and autism spectrum disorders in the Stockholm youth cohort: population based cohort study. BMJ 359:j4273. [Abstract DeVilbiss EA, Magnusson C, Gardner RM, Rai D, Newschaffer CJ, Lyall K, Dalman D, Lee BK. 2017. Antenatal nutritional supplementation and autism spectrum disorders in the Stockholm youth cohort: population based cohort study. BMJ 359:j4273.]
  14. Goodrich AJ, Volk HE, Tancredi DJ, McConnel R, Lurmann FW, Hansen FL, Schmidt RJ. 2018. Joint effects of prenatal air pollutant exposure and maternal folic acid supplementation on risk of autism spectrum disorder. Autism Res 11(1):69-80. [Abstract Goodrich AJ, Volk HE, Tancredi DJ, McConnel R, Lurmann FW, Hansen FL, Schmidt RJ. 2018. Joint effects of prenatal air pollutant exposure and maternal folic acid supplementation on risk of autism spectrum disorder. Autism Res 11(1):69-80.]
  15. Schmidt RJ, Kogan V, Shelton JF, Delwiche L, Hansen RL, Ozonoff S, Ma CC, McCanlies EC, Bennett DH, Hertz-Picciotto I, Tancredit DJ, Volk HE. 2017. Combined Prenatal Pesticide Exposure and Folic Acid Intake in Relation to Autism Spectrum Disorder. Environ Health Perspect 125(9):097007. [Abstract Schmidt RJ, Kogan V, Shelton JF, Delwiche L, Hansen RL, Ozonoff S, Ma CC, McCanlies EC, Bennett DH, Hertz-Picciotto I, Tancredit DJ, Volk HE. 2017. Combined Prenatal Pesticide Exposure and Folic Acid Intake in Relation to Autism Spectrum Disorder. Environ Health Perspect 125(9):097007.]
  16. Schmidt RJ, Iosif AM, Guerrero AE, Ozonoff S. 2019. Association of maternal prenatal vitamin use with risk for autism spectrum disorder recurrence in young siblings. JAMA Psychiatry; doi: 10.1001/jamapsychiatry.2018.3901. [Abstract Schmidt RJ, Iosif AM, Guerrero AE, Ozonoff S. 2019. Association of maternal prenatal vitamin use with risk for autism spectrum disorder recurrence in young siblings. JAMA Psychiatry; doi: 10.1001/jamapsychiatry.2018.3901.]
  17. Shin HM, Schmidt RJ, Tancredi D, Barkoski J, Ozonoff S, Bennett DH, Hertz-Picciotto I. 2018. Prenatal exposure to phthalates and autism spectrum disorder in the MARBLES study. Environ Health 17(1):85. [Abstract Shin HM, Schmidt RJ, Tancredi D, Barkoski J, Ozonoff S, Bennett DH, Hertz-Picciotto I. 2018. Prenatal exposure to phthalates and autism spectrum disorder in the MARBLES study. Environ Health 17(1):85.]

Further Reading

Stories from the Environmental Factor (NIEHS Newsletter)

Additional Resources

  • A Pioneer in Autism Research, NIEHS Expands Its Commitment (July 2023) – This article from the NIEHS Global Environmental Health Newsletter provides an overview of how NIEHS is at the forefront of funding studies on environment factors and autism.
  • Could A Gut-brain Connection Help Explain Autism? – NIH Director's Blog, January 2020.
  • Environmental Health Perspectives’ Curated Collection (June 2019) of publications covers 20 years of research that explores the potential influence of environmental risk factors on autism spectrum disorders.

  • Temple Grandin, Ph. D., of Colorado State University, gave a lecture on "Developing Individuals Who Have Different Kinds of Minds, 3rd Edition," in 2018 at NIEHS. She is a prominent researcher and author on animal behavior and internationally known speaker on autism. 

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