Why are autism rates increasing?

The UK health secretary, Wes Streeting, has told Brits to ignore what Donald Trump says about medicine after the US president claimed a link between taking paracetamol and autism.

Speaking at the White House this week, flanked by his own vaccine-sceptic health and human services secretary Robert F. Kennedy Jr, Trump said use of the painkiller Tylenol – an American brand of paracetamol – by pregnant women led to a higher risk of autism in their children.

“I trust doctors over President Trump,” Streeting told ITV’s Lorraine programme, and the claims have been widely condemned and countered by medical experts around the world, amid ongoing debate about rising rates of the neurodevelopmental disorder in the US, UK and elsewhere.

Does paracetamol cause autism?

The connection between paracetamol use and autism “has not come out of the blue”, said The Times: a “potential association between paracetamol exposure in the womb and autism had been identified in small, observational studies over the past 10 years”.

But “larger and more rigorous studies have disproved a causal link and reputable scientists are confident” the popular painkiller does not increase the risk of autism, attention deficit hyperactivity disorder (ADHD) or learning disabilities.

The largest of these studies, and the one cited by Streeting to directly dismiss Trump’s claims, was published last year and looked at 2.5 million children born in Sweden between 1995 and 2019. By comparing rates of autism between siblings where only one had been exposed to paracetamol in the womb, scientists concluded paracetamol use “was not associated with children’s risk of autism” and that previous links were likely the result of unrelated underlying factors.

Medical bodies and regulators in the US, UK and Australia have been quick to rally behind the scientific evidence, with Steven Fleischman, president of the American College of Obstetricians and Gynecologists, calling Trump’s comments “highly concerning to clinicians but also irresponsible”.

What other debunked theories have circulated?

Trump has announced a wide-ranging effort to study the causes of autism including “long-debunked claims that ingredients in vaccines or timing shots close together could contribute to rising rates of autism in the US”, reported The Telegraph.

“Without evidence”, the president claimed “that hepatitis B vaccines should not be given until children are 12 years old, and that the measles, mumps and rubella (MMR) jab should be taken ‘separately’”.

Numerous studies on hundreds of thousands of children have consistently found no link between vaccinations and autism.

This has not stopped Kennedy, who has repeatedly said the US is in the grip of an “autism epidemic” fuelled by “environmental toxins”, from singling out the Amish community – whose use of prescription drugs and rates of autism are well below average – as proof of his unsubstantiated theories.

What’s really behind the rise in numbers?

It is true that autism is being diagnosed at higher rates among children in many richer countries over recent decades, but experts say it is likely due to increased awareness, testing and the broadening definition of the neurological disorder.

Over the past 25 years autism prevalence in the US has increased from one in 150 to one in 31, according to a report on the US Centers for Disease Control and Prevention website. The trend has also been observed in other high-income countries, including the UK, Denmark, South Korea and Japan but there are “several reasons” to think this is linked to a “rise in diagnoses”, said Nature.

Since 1980, when it was first recognised as a separate mental health condition in the Diagnostic and Statistical Manual of Mental Disorders (DSM), “the diagnostic criteria for autism have broadened”, said BBC Future. Another “big shift” occurred in 2013 when “the DSM brought subcategories including Asperger’s syndrome under the umbrella of autism spectrum disorder”, meaning “people who wouldn’t previously have received an autism diagnosis now are more likely to meet the criteria”.

Diagnostic disparities have also “narrowed in groups that were historically overlooked” while the “gradual lessening of stigma is also thought to have led to more autism evaluation in children and adults”, as has a greater awareness of autism’s “many manifestations” among both members of the public and health professionals.

“More than anything”, said Nature, “research has shown that the drivers of autism are fiendishly complicated”.

“There will never be a sound-bite answer to what causes autism,” said Helen Tager-Flusberg, a psychologist who studies neurodevelopmental conditions at Boston University, Massachusetts.