Inflammation has long been associated with increased risk of Alzheimer’s disease and other types of dementia. Now a study in JAMA Network Open suggests that the increased risk may be tied specifically to inflammation from infection more than general systemic inflammation such as that caused by autoimmune disorders.
Janet Janbek, Ph.D., of Copenhagen University Hospital–Rigshospitalet and colleagues examined data amassed between 1978 and 2018 from nearly 1.5 million adults in Danish national population registries. The individuals were born from 1928 to 1953, were alive and living in Denmark on January 1, 1978, and were included in the study upon their 65th birthday. None of the individuals had a record of diagnosed dementia upon enrollment.
The researchers defined exposure as inpatient, outpatient, or emergency hospital contacts with a primary or secondary discharge diagnosis of an infection or autoimmune disease beginning at age 50.
During the study period, 45% of the individuals had infections and 9% had autoimmune diseases. Five percent developed dementia after age 65.
The researchers found that over the study period, dementia occurred about 1.5 times as often in people who had infections than in people without infections. Furthermore, the more infections people had, the higher the rate of dementia. In contrast, dementia occurred in people who had autoimmune diseases at about the same rate (1.04 times) as people without autoimmune diseases; being diagnosed with multiple autoimmune diseases did not appear to increase the rate of dementia.
“Our data and the observational nature of our study do not directly support or refute any proposed mechanism, nor can we make firm conclusions about the role of inflammation in dementia on the basis of our findings,” the researchers wrote. However, the findings “may point toward a role for infection-specific processes rather than general systemic inflammation.”
For related information, see the Psychiatric News article “History of Severe Infection Linked to Substance-Induced Psychosis.”
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