"The rates of dementia in those with schizophrenia in the study were twice that of non-schizophrenic patients," said lead researcher Hugh Hendrie, a Regenstrief Institute investigator and a scientist at the Indiana University Centre for Ageing Research.
On the other hand, while those with schizophrenia were also more likely to develop other health problems, they were less likely to get cancer.
Diagnosis and treatment improved
The study is published in the American Journal of Geriatric Psychiatry.
As the diagnosis and treatment of schizophrenia have improved, those with the mental illness are living longer, researchers noted. But there has been little information about how they fare with other conditions, such as heart problems and dementia, as they age.
So Hendrie's team, from the Regenstrief Institute and Indiana University, looked at the medical records of over 31 000 older adults, average age 70, who received care from an urban public health system, including a mental health centre, from 1999 to 2008.
Over the 10-year span, they zeroed in on 757 adults who had a diagnosis of schizophrenia from a mental health centre. (In all, 1 635 had schizophrenia, but some of those diagnoses were not confirmed at a mental health centre).
Schizophrenia, a mental illness marked by hallucinations and delusions, is typically diagnosed in adolescence or early adulthood. About 1% of the US population is affected, according to the American Psychiatric Association.
Rate of dementia
The researchers evaluated the rates of common conditions, health use costs and death rates.
They found that those with schizophrenia had higher rates of congestive heart failure: 45% versus 38% in others. They also had more serious lung problems and more instances of low thyroid function.
However, they also had lower rates of cancer, with 30% of them diagnosed with a cancer compared to 43% of other patients.
The big surprise, Hendrie noted, was the rate of dementia. Dementia was twice as common in those with schizophrenia, diagnosed in 64% of those with the mental illness compared to 32% of others.
Those with schizophrenia were also more likely to die during the follow-up period.
"The good news is those with schizophrenia are living longer; the bad news is, they are getting more of the serious physical illnesses than other people," Hendrie said.
Misinterpretation of information
Health care use was higher in those with schizophrenia, which wasn't a surprise, the researchers found. But it was surprising that those patients' admissions to hospital were almost always for physical illness, not the mental illness, Hendrie said.
He can't explain the differences. As for the dementia, he asked: "Does this really mean dementia rates are double in those with schizophrenia? Or is it that the doctors are misinterpreting the information?"
When an older person goes to a doctor who has trouble understanding what they are saying, he said, the doctor may think the person is demented, when actually the communication issues may be related to the schizophrenia.
Another possibility, Hendrie said, is that there could be a unique form of dementia that develops in a schizophrenic patient.
Hendrie also can't explain the finding of lower cancer rates. Previous studies have found lower rates of gastrointestinal cancers in those with schizophrenia, he said, and researchers have speculated that the antipsychotic medicines they take may somehow help protect against those cancers.
Integration of services
What is needed, Hendrie added, is a health care system that integrates the mental health and physical health services needed by someone with schizophrenia.
The new finding ''highlights the relationship between the brain and the rest of the body," said Dr Jeff Borenstein, president and CEO of the Brain & Behaviour Research Foundation in New York City.
Experts have known that those with schizophrenia die from medical causes at a much earlier age than those who don't, he added, but the large numbers in the study add strength to the findings. That emphasizes the need to be sure that those with schizophrenia "get treatment not only for schizophrenia, but for physical conditions as well," Borenstein said.
But, he said, "if you are not in a place where that model is in place, you can still have the benefit by making sure the physicians [for mental and physical health services] are talking with each other."