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Rachael Zimlich is a freelance writer in Cleveland, Ohio. She writes regularly for Contemporary Pediatrics, Managed Healthcare Executive, and Medical Economics.
A recent study investigates what is causing ASD to drop in wealthy, white California.
A recent study reveals that autism rates are dropping among children living in wealthy white areas of California while rising in poor, minority areas, but the reason why isn’t exactly clear.
The study,1 published in the Journal of Autism and Developmental Disorders, reviewed autism prevalence among children born in different areas of California between 1993 and 2000. Data for the study came from children in the California Department of Development Services system.
Although prevalence increased fairly equally among all the children in the study born between 1993 and 2000, the research noted that prevalence remained steady or declined in children from wealthy white areas in the years that followed. At the same time, autism prevalence continued to increase after 2000 and until the study concluded in 2013 among both white and Hispanic children in low income areas.
However, the downward trend in diagnoses among wealthier white children may not be what is appears. Rather than a natural decrease in cases, the study team suggests that perhaps the decline is more of a result of these families seeking private care for their children—therefore excluding them from the state tracking system—or making other changes that could reduce their autism risk.
“Autism was once considered a condition that occurs mainly among white children of high socioeconomic status, but my current study suggests that ethnic minorities and low income families are increasingly experiencing higher rates of autism spectrum disorder (ASD), particularly severe autism,” says Cynthia Nevison, PhD, lead author of the study and a researcher from the University of Colorado in Boulder. “The logical implication is that the etiology of ASD is primarily environmental and that ASD risk can be influenced by parental choices, behavior, and access to resources.”
Prevalence for autism nationwide is about 1 in 59, or roughly 2% of 8-year-olds in the most recent Autism and Developmental Disabilities Monitoring (ADDM) Network from 2006. In that survey, prevalence had increased from the two previous surveys in 2002 and 2004, when prevalence was 1 in 68. Another survey, the National Health Interview Survey (NHIS), estimated prevalence in 2016 at about 1 in 36 among children aged 3 to 17 years compared to a prevalence of 1 in 45 2 years prior. In comparison, estimates of prevalence in the early 1990s were 1 in 150, and 1 in 2500 in the early 1980s.
Although autism prevalence appears to have increased significantly over the decades, more recent reports have indicated that this trend may be slowing or reversing—particularly among certain socioeconomic and ethnic groups. A 2018 report2 from the Centers for Disease Control and Prevention seems to back this idea, attributing a 15% drop in ASD to a narrowing gap in prevalence between white children and children from minority groups.
Nevison and other researchers examined newer data that confirmed that autism rates were increasing faster among black and Hispanic populations when compared to white children. Historically, prevalence of autism in minority groups had been lower than among whites, but the more recent review found that the rates of autism among black children in particular had not only caught up to that of white children, but had surpassed it in most states.
To investigate further, Nevison and her colleagues examined this newest cohort, breaking down prevalence rates by race and ethnicity, as well as by county. The county-level analysis allowed for an evaluation of autism prevalence by race/ethnicity, as well as specific income groups.
Researchers found that statewide prevalence of autism in California was 1.5% by the 2013 birth year group, with the highest prevalence of 1.8% found in black children, followed by 1.7% in Asian children, 1.4% in white children, and 1.2% in Hispanic children. There was a continuous growth in prevalence throughout the cohort from 1993 to 2013, but a flattened curve was noted in all groups except for Hispanic, and most noticeably among white children. Flattening was short-lived in most of the ethnic groups, the report notes, and was shortest among black children.
In terms of wealth, the research team also noted at growth rates were similar from 1993 to 2000, but after 2000 autism prevalence decreased in the wealthiest California counties. Increases continued but were slower in middle income areas, and were consistent across the study years in low income counties.
The finding in this study that autism prevalence among black children matched and then exceeded that of white children challenges previous theories that increased prevalence is a function of autism awareness and access to care, according to the report. Black and Hispanic children have typically had lower access to care, but increased emphasis on services for low income children may have helped to close these gaps in care.
A number of theories have been proposed to explain the differences in autism prevalence in various socioeconomic areas including, genetics, environments, access to care, and therapy choices. There is also a link to risk factors that could have an impact based on socioeconomic factors including immune inflammation and oxidative stress, diet quality, chronic stress, and more.
“Rising ASD rates among minority children generally are interpreted to suggest that these children have been underdiagnosed in the past and are now catching up to wealthy, white children due to better pediatric screening and awareness. There is likely truth to that view, but it also involves questionable assumptions, such as that there is a natural or genetic level of ASD prevalence in the population, that white ASD rates have more or less stabilized at that level, and that minorities are now catching up thanks to improved screening and will stabilize at a similar level. Those assumptions aren’t supported by data showing that minority ASD rates are surpassing white rates in many states and counties, and that ASD rates among low income whites are continuing to increase.”
Nevison says an alternative explanation is that minority children didn’t experience ASD at the same level as wealthy white children in the past, and that prevalence is genuinely increasing in this population.
“The fact that my study used an age-resolved snapshot from 2019—in which older minority children in that snapshot had lower rates of diagnosed ASD in 2019 than younger children—supports this latter, alternative explanation,” Nevison. “However, pediatricians might consider whether ASD has been missed or underdiagnosed in their older patients, especially among minority children and teenagers.”
This means ASD would join a number of other conditions like diabetes, asthma, and obesity that are more prevalent among the poor as a result of toxin exposure, poor diets, and other factors that lead to chronic inflammation.
The authors lean toward the conclusion that wealthy, educated parents in predominantly white areas likely opted out of public services programs for their children and began making lifestyle and care choices that lowered their likelihood of an autism diagnosis. Nevison says some of the changes observed in those communities as ASD cases fell could be implemented in lower income areas, but it would take a concerted effort to identify the environmental factors that cause ASD.
“Historically about 95% of ASD research funding has gone toward genetics. Many research institutions are still largely following a paradigm that views ASD as a genetic rather than an environmental condition,” Nevison says. “Wealthy parents in California appear to have moved beyond that paradigm and succeeded in lowering their children’s ASD risk. Hopefully the research community can follow their lead and conduct studies to understand what these parents have been doing.”
Nevison says other studies3 have also suggested a breakdown of ASD trends along private versus public insurance lines. She says she hopes her study will motivate more research, and inspire clinicians to examine their own practices and those in their communities.
“This may simply reflect underlying socioeconomic factors, as mentioned above, but may also suggest that children on Medicaid and Children's Health Insurance Program are receiving a lower standard of care than privately insured children,” she says. “Pediatricians in clinical practice might consider whether they are treating lower income and minority children differently than wealthier white and Asian children and move to address those disparities.”
1. Nevison C, Parker W. California autism prevalence by county and race/ethnicity: declining trends among wealthy whites. J Autism Dev Disord. March 19, 2020. Epub ahead of print. doi:10.1007/s10803-020-04460-0
2. Christensen D, Baio J, Braun K, et al. Prevalence and characteristics of autism spectrum disorder among children aged 8 years — Autism and Developmental disabilities Monitoring Network, 11 Sites, United States, 2012. MMWR Surveillance Summaries. 2016:65(3):1-23. doi:10.15585/mmwr.ss6503a1
3. Pearl, M., Matias, S., Poon, V., & Windham, G. Trends in birth prevalence of autism spectrum disorder (ASD) in California from 1990 to 2010, by race-ethnicity and income. Poster presented at: 2019 International Society for Autism Research Annual Meeting; May, 2010; Montreal, Canada.