People diagnosed with attention deficit hyperactivity disorder may die up to 11 years earlier than those without the condition, a study suggests.
Researchers at University College London (UCL) found a reduction in life expectancy in men with ADHD of between four and a half and nine years, and in women between six and a half and 11 years.
Although the reason is unclear, experts say those diagnosed often engage in unhealthy habits and struggle to access health care.
"It is deeply concerning that some adults with diagnosed ADHD are living shorter lives than they should," said Prof Josh Stott, of the department of psychology & language sciences at UCL.
"People with ADHD have many strengths and can thrive with the right support and treatment.
"However, they often lack support and are more likely to experience stressful life events and social exclusion, negatively impacting their health and self-esteem," he added.
Around 2.6 million people in Britain are thought to have ADHD - 694,000 children, and 1.9 million adults - but many remain undiagnosed.
Those with the condition struggle to focus on mundane tasks, leading to impulsiveness, restlessness and time management problems which make it harder to succeed in education.
ADHD often occurs alongside learning disorders, anxiety and depression and it can raise the risk of obesity, substance abuse and heart problems.
Philip Asherson, professor of molecular psychiatry at King's College London, who was not connected with the study, said: "We know that ADHD is associated with higher rates of smoking, obesity, cardiovascular disease and cancer among other health problems.
"Adults with ADHD are more likely to engage in unhealthy habits such as binge eating or smoking and risk-taking behaviour.
"Services to support adults with ADHD and improve physical and mental health outcomes lag behind those for other common conditions such as anxiety, depression, hypertension and obesity.
"Of particular concern are limited access to diagnosis and treatment including psychosocial support. Until this is addressed the shorter life expectancy demonstrated in this study is likely to continue."
A previous survey of British adults aged 16 to 64 found that a third of those with ADHD traits needed medication or counselling for a mental health problem, compared with 11 per cent of people without ADHD.
However, eight per cent those diagnosed said they had struggled to get mental health treatment, compared with one per cent of those without the condition who had requested help.
"Although many people with ADHD live long and healthy lives, our finding that on average they are living shorter lives than they should indicate unmet support needs," said Dr Liz O'Nions, of UCL.
"It is crucial that we find out the reasons behind premature deaths so we can develop strategies to prevent these in future."
For the new study, researchers looked at the health records of more than 30,000 Britons who had been diagnosed with ADHD and compared them with 300,000 people without a diagnosis.
Although the study found an increased risk of dying earlier they had no information about the cause of death.
Oliver Howes, professor of molecular psychiatry at King's College said: "These findings highlight the need for much more investment in mental health services so people can get the help they need.
"The study adds to lots of other evidence that people with other mental illnesses die sooner than people without mental illness to show this for ADHD as well."
The research was published in The British Journal of Psychiatry.