This older group exhibited the highest rates of missed diagnoses, with 96.29% of autistic men and 97.19% of autistic women over 60 not receiving a proper diagnosis.

The 40 to 59 age group followed closely, with 91.45% of autistic men and 79.48% of autistic women not diagnosed. In the 20 to 39 age category, diagnostic rates significantly improved, with only 53.17% of autistic men and 49.27% of autistic women not recognized.

The study concluded that autistic adults beyond 40 years old are 89% undiagnosed overall.

Dr. Gavin Stewart, British Academy Postdoctoral Research Fellow at the IoPPN and lead author of the review, commented: “These extremely high underdiagnosis estimates indicate that many autistic adults have never been recognized as autistic and have not been offered appropriate support. This could make them more vulnerable to age-related issues, such as social isolation and poorer health.

“The high rates of underdiagnosis also suggest that much of our research has systematically overlooked a large portion of the autistic population, potentially distorting our understanding of how autistic people age and leaving crucial gaps in policy and services.”

The research revealed that middle-aged and older autistic people experience higher rates of nearly all physical and mental health conditions compared to non-autistic adults.

These include immune diseases, cardiovascular disease, neurological disorders, gastrointestinal disorders, anxiety and depression, alongside conditions linked to advancing age, including Parkinson’s disease, cognitive disorders, osteoporosis and arthritis.

Older adults displaying high autistic traits were also six times more prone to experiencing suicidal ideation, thoughts of self-harm and self-harm.

The results further indicated these adults were four times more likely to receive an early onset dementia diagnosis than non-autistic people. Autistic adults experienced worse outcomes in employment before retirement, relationships and overall quality of life, owing to high levels of social isolation.

The review also discovered they encountered obstacles to accessing healthcare support because of autistic characteristics such as communication differences, sensory sensitivities, uncertainty about service access and limited knowledge of autism in adulthood among medical professionals.

Professor Francesca Happé, Professor of Cognitive Neuroscience at the IoPPN and co-author of the review, added: “Understanding the needs of autistic people as they age is a pressing global public health concern. 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 ageing autistic people can live happy and healthy lives.”

The researchers called for more studies and investigations to better understand the experiences of autistic people in midlife and older age. This can help improve outcomes for autistic people as they age.

If you believe you have signs of autism, the NHS recommends speaking to a health professional such as a GP and ask about being referred for an autism assessment. This is conducted by autism specialists who may ask about problems you are having, speak to people you know or observe how you interact with other people.

Receiving a diagnosis can provide clarity on why your perception and experiences of the world differ from others, enable you to access support and potentially even financial benefits. It can also assist in explaining to others why you perceive and experience the world differently.