Infections more likely indicator of dementia than autoimmune disease

Key takeaways:

• A Danish population-based study examined records of more than 1.4 million residents from 1978 to 2018.
• Researchers found that infections, rather than autoimmune conditions, were better predictors of dementia.

Infection-specific processes, rather than general systemic inflammation, may play a role in the development of dementia among those with hospital-diagnosed infections, according to research from JAMA Network Open.

“There has been extensive debate about whether infections might be causally linked to dementia, particularly Alzheimer’s disease,” Janet Janbek, PhD, of the Danish Dementia Research Center, department of neurology, Copenhagen University Hospital in Denmark, and colleagues wrote. “A large body of literature supports a role for systemic inflammation in increased dementia risk and includes epidemiological studies of diseases that induce a proinflammatory state.”

Janbek and fellow researchers aimed to investigate the associations of infections diagnosed in hospital and autoimmune diseases with incidence of dementia incidence and to examine the possibility of concurrence within the immune system among both conditions.

They conducted a retrospective cohort study examining records from population-based Danish national registries from the years 1978 to 2018 that included 1,493,896 Danish residents (51% female; 45% with infections; 9% with autoimmune diseases; 5% with dementia) born from 1928 to 1953, alive and in the country on Jan. 1, 1978, and again at the time of their 65th birthday. Among individuals with infections, 343,504 (51%) were men, whereas among those with autoimmune diseases, 77,466 (61%) were women.

The study’s primary outcome was incidence of all-cause dementia, indexed as a first diagnosis after an individual within the registry reached 65 years of age. Janbek and colleagues utilized Poisson regression with person-years at risk as an offset variable to measure time to initial diagnosis of dementia.

Results showed that the dementia incidence rate ratio following any infection was 1.49 (95% CI, 1.47-1.52) and increased consistently with rising numbers of infections in a dose-dependent manner. Dementia rates were also shown to increase for all infection sites in the short term, but in the long term, this increase was not consistent.

Data additionally showed dementia IRR following any incidence of autoimmune disease was 1.04 (95% CI, 1.01-1.06), but no dose-dependent increase was observed, with few autoimmune conditions demonstrating increased IRRs for dementia.

“To our knowledge, this study is the first to assess all sites of infection, the long-term and short-term risks across all sites, and the burden of infection and autoimmune disease using multiple measures,” Janbek and colleagues wrote.