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Analysis shows higher risk for dementia among individuals with schizophrenia

Results from a population-based cohort study indicate individuals with schizophrenia, particularly those aged younger than 65 years, had increased relative risk for dementia that was not explained by dementia risk factors.

“The association between schizophrenia and the risk of subsequent dementia remains unclear. Four prior studies have compared the risk of dementia among persons with vs. those without schizophrenia using clinical dementia diagnoses, and their findings ranged from a 2.4-fold to a 16-fold higher risk of developing dementia,” Anette Riisgaard Ribe, MD, of Aarhus University, Denmark, and colleagues wrote. “However, those studies were limited because they did not include individuals with onset of schizophrenia before the age of 30 years … or had an insufficient duration of follow-up for the cohort to display a clinically significant risk of developing dementia.”

Researchers analyzed data from six nationwide registers in Denmark for more than 2.8 million individuals aged 50 years of older. Of these, 20,683 had schizophrenia. Researchers followed study participants from January 1995 to January 2013.

During 18 years of follow-up, 944 individuals with a history of schizophrenia developed dementia.

After adjusting for age, sex and calendar period, schizophrenia was associated with more than 2-fold higher risk for all-cause dementia (IRR = 2.13; 95% CI, 2-2.27).

This effect did not change when adjusting for medical comorbidities such as cardiovascular diseases and diabetes (IRR = 2.01; 95% CI, 1.89-2.15) but slightly decreased when adjusting for substance abuse (IRR = 1.71; 95% CI, 1.6-1.82).

Researchers found that individuals aged younger than 65 (IRR = 3.77; 95% CI, 3.29-4.33), males (IRR = 2.38; 95% CI, 2.13-2.66), individuals living with a partner (IRR = 3.16; 95% CI, 2.71-3.69), those without cerebrovascular disease (IRR = 2.23; 95% CI, 2.08-2.39) and those without substance abuse (IRR = 1.96; 95% CI, 1.82-2.11) had higher risk ratios for dementia.

Cumulative incidence proportions for developing dementia by age 65 years was 1.8% (95% CI, 1.5-2.2) for individuals with schizophrenia and 0.6% (95% CI, 0.6-0.7) for those without schizophrenia.

“It is clear that individuals with schizophrenia develop dementia at a higher-than-expected rate and at younger ages than those without schizophrenia. The majority do not undergo cognitive decline, suggesting that this heterogeneous syndrome belies a subgroup with a condition that is both neurodevelopmental and degenerative,” Constantine G. Lyketsos, MD, MHS, and Matthew E. Peters, MD, of Johns Hopkins Bayview Medical Center, Baltimore, wrote in an accompanying editorial. “Ultimately, understanding schizophrenia will require breaking apart its etiologic heterogeneity. Focusing on the individuals who develop progressive dementia could be a successful approach that will provide clues to the etiology of this diverse condition.” – by Amanda Oldt

Disclosure: Riisgaard Ribe and colleagues report no relevant financial disclosures. Lyketsos reported receiving grant support (research or continuing medical education) from the NIMH, the National Institute on Aging, Associated Jewish Federation of Baltimore, Weinberg Foundation, Forest, GlaxoSmithKline, Eisai, Pfizer, AstraZeneca, Lilly, Ortho-McNeil, Bristol-Myers, Novartis, the National Football League (NFL), Elan, and Functional Neuromodulation; serving as a consultant or advisor to AstraZeneca, GlaxoSmithKline, Eisai, Novartis, Forest, Supernus, Adlyfe, Takeda,Wyeth, Lundbeck, Merz, Lilly, Pfizer, Genentech, Elan, the NFL Players Association, the NFL Benefits Office, Avanir, Zinfandel, Bristol-Meyers Squibb, AbbVie, Janssen, Orion, Otsuka, Servier, and Astellas; and receiving honoraria or travel support from Pfizer, Forest, GlaxoSmithKline and Health Monitor.