Double Trouble: Depression Plus Diabetes Boosts Dementia Risk

Megan Brooks

April 16, 2015

Depression and diabetes each independently raise the risk of developing dementia, and having both conditions poses the greatest risk, particularly in people younger than 65 years, according to a Danish population-based study.

In this subgroup, a quarter of all cases of dementia may have been directly attributable to the combination of diabetes and coexisting depression, investigators led by the late Wayne Katon, MD, Department of Psychiatry and Behavioral Sciences, University of Washington School of Medicine, Seattle, note.

"Our findings are very important for both patients and their healthcare providers," Dimitry S. Davydow, MD, MPH, also of the Department of Psychiatry and Behavioral Sciences, University of Washington School of Medicine, told Medscape Medical News.

"Arguably, the best treatment available for dementia is to prevent it from developing. If it turns out through future research that what we have found in our study documents a true, causal link between diabetes, depression, and dementia, then there is the potential that successfully treating these illnesses could prevent future cases of dementia and improve quality of life for millions of individuals worldwide," Dr Davydow said.

The study was published online April 15 in JAMA Psychiatry.

Double Whammy

Diabetes and depression are both known to be potential risk factors for developing dementia, but until now it was unclear to what extent each independently raised the risk of developing dementia and to what extent having both conditions increased an individual's subsequent risk of dementia. "We sought to answer these questions with this study," Dr Davydow said.

The researchers examined health data for more than 2.4 million Danish citizens aged 50 years or older, including 477,133 (19.4%) with depression, 223,174 (9.1%) with diabetes, and 95,691 (3.9%) with both. During 13,834,645 person-years of follow-up, 59,663 adults (2.4%) developed dementia.

Compared with adults who did not have diabetes or depression, the risk for dementia was 20% higher in those with diabetes alone (hazard ratio [HR], 1.20; 95% confidence interval [CI], 1.17 - 1.23), 83% higher in those with depression alone (HR, 1.83; 95% CI, 1.80 - 1.87), and 117% higher in those with both conditions (HR, 2.17; 95% CI, 2.10 - 2.24), after adjustment for age, sex, calendar period, and marital status. The estimates decreased only slightly after further adjustment for chronic diseases.

Among adults younger than 65 years, the HRs for dementia were 2.93 (95% CI, 2.71 - 3.16) with depression alone, 1.71 (95% CI, 1.49 - 1.97) with diabetes alone, and 4.84 (95% CI, 4.21 - 5.55) with comorbid depression and diabetes.

Among all cases of dementia diagnosed in Denmark in adults aged 50 years or older from 2007 through 2013, 6% were potentially due to the combination of having both diabetes and depression, the researchers report. And for individuals younger than 65 years, 25% of all cases of dementia may have been directly attributable to the combination of diabetes and coexisting depression, they say.

Early Diagnosis Critical

"Diabetes and depression are both diagnosable and treatable conditions, and both can improve significantly with the right treatments. However, we don't do a very good job of diagnosing either diabetes or depression early," said Dr Davydow.

"Too frequently, diabetes isn't found until patients have already had complications, and depression isn't addressed until it is interfering with care for medical conditions, causing problems with relationships and/or work/school, and/or resulting in suicide," he added.

Dr Davydow believes the observed risks for individuals younger than 65 years who have both diabetes and depression are "particularly concerning in light of the rates of obesity and associated chronic illnesses in the United States and further highlight the need to improve recognition and treatment of medical conditions and coexisting psychiatric conditions, such as depression, in order to help prevent a potential tsunami of dementia over the next several decades."

In an invited commentary, Charles F. Reynolds III, MD, of the University of Pittsburgh Medical Center, in Pennsylvania, writes that the study "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. 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."

The study was funded by the Lundbeck Foundation and the National Institutes of Health. The authors report no relevant financial relationships.

JAMA Psychiatry. Published online April 15, 2015. Abstract, Commentary

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