Type 2 diabetes and depression are linked to an increased risk for dementia, with risk being even higher for those with both conditions vs. those without either one, study results published in JAMA Psychiatry indicate.
Both depression and type 2 diabetes are very common in Western populations, with as many as 20% of people with type 2 diabetes also having comorbid depression, according to background information in the study.
To more closely examine the potential relationship between these conditions, researchers compared dementia risk in a national, population-based cohort of more than 2.4 million Danish citizens aged at least 50 years who did not have dementia from 2007 to 2013.
Of all participants, 477,133 (19.4%) had depression, 223,174 (9.1%) had diabetes and 95,691 (3.9%) had both. Average at initial diagnosis of type 2 diabetes was 63.1 years and average at initial diagnosis of depression was 58.5 years, according to the data.
During more than 13 million person-years of follow-up, 59,663 participants (2.4%) developed dementia. Of these, 6,466 (10.8%) had diabetes, 15,729 (26.4%) had depression and 4,022 (6.7%) had both, the researchers reported.
Results revealed that the adjusted HRs for all-cause dementia were 1.83 (95% CI, 1.80-1.87) for those with depression, 1.20 (95% CI, 1.17-1.23) for those with diabetes and 2.17 (95% CI, 2.10-2.24) for those with both conditions, as compared with those without depression or diabetes.
The researchers also found that the excess risk for all-cause dementia in those with both diabetes and depression exceeded the summed risk associated with each condition individually. This was especially true, the researchers noted, for people aged younger than 65 years (HR=4.84; 95% CI, 4.21-5.55).
Data showed that corresponding attributable proportion due to interaction of comorbid depression and diabetes was 0.25 (95% CI, 0.13-0.36) in those aged younger than 65 years and 0.06 (95% CI, 0.02-0.10) for those aged 65 years or older.
“In light of the increasing societal burden of chronic diseases, further research is needed to elucidate the pathophysiologic mechanisms linking depression, [type 2 diabetes] and adverse outcomes such as dementia and to develop interventions aimed at preventing these dreaded complications,” the researchers wrote.
In an invited commentary, Charles F. Reynolds III, MD, of the University of Pittsburgh Medical Center, placed these findings in context and highlights areas of future research.
“The study by Katon and colleagues illustrates the need for convergent scientific approaches to meet the challenge of promoting healthy brain aging and cognitive fitness into the last years of life,” Reynolds wrote. “The convergence of expertise from epidemiology, behavioral and basic science in the biology of aging and brain health are all necessary ‘to move the needle’ in the demographic challenge that confronts the entire globe.”