By some estimates people with schizophrenia will die, on average, 15 to 20 years earlier than the general population. Although schizophrenia is associated with several age-related disorders and considerable cognitive impairment, studies comparing the risk of dementia among people with schizophrenia versus those without have produced mixed results.
Using nationwide registers in Denmark, researchers from Aarhus University in Denmark and the University of Washington tracked the outcomes of more than 2.8 million people aged 50 and older—20,683 of whom had or developed schizophrenia over the course of the study—for up to 18 years. Overall, 136,012 individuals developed dementia, including 944 individuals with a history of schizophrenia.
After adjusting for age and sex, schizophrenia was found to be associated with a more than two-fold higher risk of dementia when compared with persons without schizophrenia. The relative risk of dementia was almost four-fold higher among individuals younger than 65 years. In absolute numbers, 7.4 of 100 people with schizophrenia developed dementia before the age of 80 years compared with 5.8 of 100 people without schizophrenia.
The risk of dementia in people with schizophrenia was only slightly reduced when adjusting for substance abuse disorder but was unaffected by adjustment for medical comorbidities including cardiovascular disease and diabetes.
“It is clear that individuals with schizophrenia develop dementia at a higher-than-expected rate and at younger ages than those without schizophrenia,” wrote Constantine Lyketsos, M.D., M.H.S., and Matthew Peters, M.D., both of Johns Hopkins University in a related editorial. Still, they noted, “[t]he majority do not undergo cognitive decline, suggesting that this heterogeneous syndrome belies a subgroup with a condition that is both neurodevelopmental and degenerative. … Focusing on the individuals who develop progressive dementia could be a successful approach that will provide clues to the etiology of this diverse condition.”
For related information, see the Psychiatric News article “Neuropsychiatric Symptoms Implicated in Conversion From MCI to Dementia.”
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