(AP) -- Some 38 percent of Europeans, or 165 million people, suffer from mental illness or neurological disorders on a broad spectrum ranging from anxiety to dementia, a new study published Tuesday says. Most are not being treated, though some experts said many may not need psychiatric help.
Researchers drew on previous surveys of mental health and applied specific criteria to determine how many people had a disorder. The data covered more than 500 million people in the 27 European Union countries plus Switzerland, Iceland and Norway, according to the study paid for by the non-profit European College of Neuropsychopharmacology.
More than 90 different mental and neurological problems were considered, including those often found in children, such as attention deficit hyperactivity disorder, to those often found in the elderly, such as the dementia in Alzheimer's patients.
Using such a broad definition of mental health and neurological disorders might artificially inflate the problem, some experts said.
"Not all of these people require psychiatric interventions," said Matt Muijen, a mental health expert at the World Health Organization's European office in Copenhagen who was not linked to the research. "The 38 percent is indicative of stress in society, not necessarily psychiatric disorders."
Because researchers in other areas use varying definitions of what constitutes a mental health problem, it is hard to compare European rates to those elsewhere, he said. In the U.S., for example, the National Institute of Mental Health estimates about 26 percent of adults have some type of mental disorder.
The rates of mental and neurological disorders didn't appear to be rising, compared to a similar study in 2005. The most common problems include anxiety disorders, insomnia, depression, alcohol and drug dependence and dementia. Experts estimated only one-third of people receive treatment.
Other experts said the numbers of people with mental health problems appeared higher than what is commonly believed because most patients don't report their illness and because this study includes disorders in children and the elderly.
"Although the figure seems shockingly high, this is the most rigorous study done in Europe," said Graham Thornicroft, a professor of community psychiatry at the Institute of Psychiatry at King's College London. He was not linked to the study.
"The real tragedy is that so few people with mental health problems receive treatment," Thornicroft said.
Hans-Ulrich Wittchen, one of the study's authors, said many patients still face discrimination and limited services when seeking treatment.
"Mental health disorders are Europe's largest health care challenge in the 21st century," he said.
The study was published in the group's journal, "European Neuropsychopharmacology," and presented at its annual meeting in Paris on Tuesday. None of the study's authors reported a conflict of interest.
Explore further: The size and burden of mental disorders in Europe