Around 90% of autistic adults over 40 are undiagnosed in UK, researchers find

Some 89 to 97 per cent of autistic adults aged over the age of 40 are undiagnosed in the United Kingdom, the largest report of its kind has found.

While autism is now commonly recognised and diagnosed in childhood, many older adults grew up without the same awareness or assessments available today, leaving them to navigate middle and later life without the support that a diagnosis can bring.

The review, published this week in the Annual Review of Developmental Psychology, found that older autistic adults consistently face higher rates of physical and mental health conditions, as well as challenges around employment, relationships and life events such as menopause and retirement.

Dr Gavin Stewart, co-lead of the Re: Spect Lab at King’s College London and lead author of the review, told Euronews Health:

“Autism in older age is often overlooked. Over the past decade or so, there’s been rapid interest in what happens to autistic people as they age”.

The hidden health risks of autism in adults

The review collated evidence showing that middle-aged and older autistic adults have higher rates of immune diseases, cardiovascular disease, neurological disorders, gastrointestinal disorders, anxiety and depression. They are also more likely to develop conditions typically linked with ageing, such as Parkinson’s disease, osteoporosis, and arthritis.

Some of the findings are particularly alarming. Data showed that older adults with high autistic traits are six times more likely to experience suicidal thoughts or self-harm, and four times more likely to be diagnosed with early-onset dementia.

Life expectancy was also found to be lower: autistic people in the UK live to an average age of 75 compared to 81 for non-autistic people. The authors caution, however, that these figures may be skewed by high levels of underdiagnosis.

"Part of this may be genetic, since many conditions share common genetic factors. But a large part comes from external challenges: stigma, barriers to education and employment, social isolation, and even difficulties accessing physical exercise," Stewart explained.

"All of these create a knock-on effect that worsens both mental and physical health”.

Why so many cases go undiagnosed

Autism was first clinically described in the 1920s and 1940s, but not formally included in diagnostic manuals until the 1960s. Stewart said this historical lag explains why so many older adults were missed.

Today, autism spectrum disorder is defined as "a neurological and developmental disorder that affects how people interact with others, communicate, learn, and behave," according to the National Institute of Mental Health research organisation.

“Autism is still a relatively new diagnostic label. So a lot of young people who were born in the 1960s were overlooked under the very narrow, very stringent criteria that autism once had. It’s really just a case of our improved understanding and recognition of autism,” it adds.

Although autism rates have risen sharply in recent decades – in 2022, one in every 31 American children under eight was diagnosed – researchers say this is largely due to better awareness and wider diagnostic criteria rather than a genuine increase.

A 2021 study in the United Kingdom, meanwhile, found that between 1998 and 2018, there had been a 787 per cent increase in autism diagnoses.

Calls for better support

Research into ageing in autistic populations has increased almost fourfold since 2012, but just 0.4 per cent of all autism research since 1980 has focused on people in midlife or older age.

Stewart warned that more investment is urgently needed in support and services.

“The support offerings are a really important area that needs a lot more research. We need to know what kind of support people want, how best to implement it, and how to make sure people aren’t falling through the cracks – whether that’s healthcare access or wider issues like social isolation".

He added that there’s also a big piece of work needed around awareness and identifying undiagnosed autistic people.

"If we’re looking at around 90 per cent of people over 40 being undiagnosed, that’s a huge population not getting the support they need," Stewart said.