Do risk of dementia increase substantially when depression and diabetes occur together? JAMA Psych. June, 2015.

16 06 2015

Diabetes (DM) affects up to 14% of Western population. 25% of women and 16% of men will have  depression during their life time. Depression and diabetes  often co occur . The link between DM and depression is bidirectional. It is also known that both disorders contribute to an increased risk for vascular complications.

Depression and DM – both are  strong independent risk factors for dementia. DM increase risk for all cause dementia by 47%. Depression  doubles the subsequent risk for all-cause dementia. What about the combination of DM and depression?
Studies on patients with DM have shown that those who also have depression are at a high risk of dementia. Further clarity on this would be gained if large cohorts of individuals could be studied for risk for all-cause dementia among persons with DM, depression, or both compared with persons who had neither illness.

A Danish study ( by researchers from Seattle and Copenhagen) using national cohort of 2.4 million people has done just this.All living Danish citizens 50 years or older who were free of dementia at January 2007  were followed up until  December, 2013 .Danish psychiatric central register identified individuals with a diagnosis of depression or who have been prescribed with antidepressants. National diabetes register identified those diagnosed with DM .

Results

19 % had a diagnosis of depression. 9 % received a diagnosis of DM, and 4%  had  comorbid depression and DM.The mean age at the initial diagnosis of DM was 63  years. Mean age  at the initial diagnosis of depression was 59  years. 2.4% developed  dementia, of this, 26% had depression alone,11% had DM alone, and 7%  had comorbid depression and DM.

Depression alone, contributed  83% greater risk of dementia. DM alone was associated with a 20% greater risk for all-cause dementia.  Depression and DM the risk was higher:  a 117% greater risk. This combined effect is more pronounced  in younger people. The combined effect of these two  illness exposures on all-cause dementia risk was larger than the sum of the 2 individual diseases.

One  limitation is  the lack of information on possible confounders such as health-risk behaviors ( smoking, obesity, and sedentary  lifestyle) .These can well be mediators of the association.

Comments: Depression alone is associated with the highest relative risk for all-cause dementia. Individuals with depression and DM need to consider engaging in neuro protective activities.  Physical activity is  increasingly well established as an effective strategy. It have  anti-inflammatory effects and it promotes  neurovascular health.

Summary of the article:

Effect of depression and diabetes mellitus on the risk for dementia: a national population-based cohort study.

Katon W, Pedersen HS, Ribe AR, Fenger-Grøn M, Davydow D, Waldorff FB, Vestergaard M.

JAMA Psychiatry. 2015 Jun 1;72(6):612-9

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