Autism diagnoses have increased sharply in recent decades, leading to speculation that the condition is new or triggered by modern environmental factors. But a comprehensive review of research on autistic adults over the age of 40 paints a very different picture, showing that autism spans older generations, with as many as 90% of cases going undiagnosed.
Researchers from King's College London (KCL) have unearthed the startling figure in a new study focused on what we know about autism in midlife and older age. They found that the vast majority of autistic people over 40 remain undiagnosed, which has significant consequences for health, wellbeing and quality of life. Studies have found that autistic individuals have a four times higher risk of early dementia, six times higher risk of suicidal ideation and a life expectancy that falls six years short of their non-autistic peers (in the UK, 75 years compared to 81 years).
In the study, UK health record analyses revealed that around 89% of autistic adults aged 40-59 years – and a massive 97% of those over 60 – do not have a formal diagnosis. Essentially, nine out of 10 older autistic adults may be living with the condition without any acknowledgement of it or help.
"These very high underdiagnosis estimates suggest that many autistic adults will have never been recognized as being autistic, and will have not been offered the right support," said lead author Dr Gavin Stewart, a researcher from KCL. "This could make them more susceptible to age-related problems, for example being socially isolated and having poorer health."
In addition to mental health challenges, older autistic adults have higher rates of a suite of serious conditions, including immune diseases, cardiovascular disease and gastrointestinal disorders, as well as age-related issues like Parkinson’s disease, osteoporosis and arthritis.
In the UK, there was a 787% increase in autism spectrum disorder (ASD) diagnoses between 1998 and 2018, though this was largely made up of children, teens and younger adults. While the study is focused on the UK, there's a similar pattern across the globe. According to the Centers for Disease Control and Prevention (CDC), one in 150 children born in 1994 had a diagnosis when data was assessed in 2000. Now, around one in 31 kids born two decades later, in 2014, had received an autism diagnosis (data assessed in 2020).
"In the US, ASD diagnosis rates increased substantially between 2011 and 2022, particularly among young adults, female children and adults, and children from some racial or ethnic minority groups," noted scientists in a 2024 study. "Diagnosis prevalence trends generated using health system data can inform the allocation of resources to meet the service needs of this growing, medically complex population."
However, despite the rise in awareness and diagnoses around the world, older adults remain unrecognized in the statistics. And a leading reason lies in how autism was historically defined. For much of the 20th century, ASD was narrowly described as “infantile autism,” now an outdated term, and often linked to intellectual disability. And like attention-deficit/hyperactivity disorder (ADHD), the psychiatric focus was on males. Diagnostic criteria for ASD gradually broadened from the 1980s onwards, capturing a more accurate picture of the spectrum. This means that today’s rise in autism prevalence is largely explained by changes in recognition, criteria and awareness.
“The high rates of underdiagnosis also mean that much of our research has systematically overlooked a large proportion of the autistic population, potentially skewing our understanding of how autistic people age, and leaving critical gaps in policy and services," said Stewart.
In a US study, researchers found that 35.1% of autistic adults aged 64 and older also had a dementia diagnosis. In the general population, about 10% of people over 65 years have dementia, with rates rising to roughly one-third among those over 85. Scientists don't yet fully understand why people with ASD have such a higher risk of cognitive decline.
In this latest study, the researchers found that in addition to poorer health outcomes compared with the general population, older adults faced challenges with access to healthcare and support, with diagnosis and treatment still skewing towards children. They also had a higher rate of issues when it came to later-life employment and relationships. Around 20% of autistic adults over the age of 40 report being socially isolated, compared with 4% of non-autistic peers.
While there remains a sizable gap in research when it comes to ASD among older individuals, this study makes a serious case for better understanding of the experiences of autistic people in midlife and beyond in order to improve health and quality of life outcomes for people across their lifespan.
It also serves as a timely reminder that claims of an “autism epidemic” ignore the hidden generations of older adults who were simply never diagnosed and remain largely invisible to clinicians and policymakers.
"Understanding the needs of autistic people as they age is a pressing global public health concern," said co-author Francesca Happé, Professor of Cognitive Neuroscience at KCL. "As autistic people age, the nature of the challenges they face changes. We must adopt a lifespan approach that funds long-term research, integrates tailored healthcare, and expands social supports so that aging autistic people can live happy and healthy lives."
The research was published in the Annual Review of Developmental Psychology.
Source: King's College London
