Diabetes, Depression, and Dementia Link

The diagnosis and treatment of depression in the elderly population with type 2 diabetes are essential for managing dementia risks.  

As health care providers, when we consider our elderly population, we think about renal dose adjustment, hepatic adjustments, cardiovascular diseases, complications in their health, drug interactions, etc. In this case, we are talking about patients with type 2 diabetes who were diagnosed with depression and are at risk of dementia. Some researchers are trying to find the links between these three health conditions that are very important to maintain under control to keep our elderly population healthy as possible. Depression is up to two times as common in patients who have type 1 or type 2 diabetes, and a variety of reasons are behind this. About 20% of patients with type 2 diabetes develop depression at some point. The stresses of managing diabetes can lead to the development of depression; even more, being depressed can alter the way patients eat, their performance, their behavior, and other factors that can change their glycemic control when they are all combined. In the past few years, another link has been found. Some studies have shown an association in patients with type 2 diabetes who have been diagnosed with depression and the incidence of dementia, and examined the role of inflammatory cytokines when managing dementia risks.   

A prospective cohort study evaluated the relationship between type 2 diabetes, depression and dementia, and the role of inflammatory markers in patients from an older cohort study. In 2006 and 2007, the research included 1066 patients from ages 60 to 75 years old and with type 2 diabetes; the researchers evaluated and conducted a follow-up four years and ten years later. This study uses the Hospital Anxiety and Depression Scale (HADS scale) to determine if a patient has depression; specifically, the subdivision HADS-D. A HADS-D score of ≥8 defines depression, whereas a HADS-D score of ≥11 represents severe depression. They identified dementia using the ICD-10 dementia codes, electronic medical records, and death certificates, showing dementia as the primary or secondary cause of death. The inflammatory biomarkers evaluated in the study include CRP, IL-6, TNF-α, and fibrinogen. This study’s statistical tests include the t-test, the Mann-Whitney U test, the X2 test, and Cox proportional hazards models. Data was also adjusted for age, sex, BMI, and other comorbidities.  

The study results included 1002 participants who went to evaluation after finalizing exclusions. Of the 1002 participants, 116 had depression and 24 severe depression. In the 116 participants with depression, there was a statistically significant association with the increase in inflammatory markers, especially CRP, IL-6, and fibrinogen. In the 24 participants with severe depression, the only statistically significant association observed was with CRP. When evaluating the incidence of dementia in these patients, 105 participants developed this condition after a follow-up conducted ten years from screening. The majority of them were older male patients. 21% of these patients were diagnosed with depression, and from the 371 deaths reported in 10 years follow-up, 41 deaths were from patients diagnosed with dementia. After adjustments in data, the study showed that patients with type 2 diabetes who developed depression have a 2.5-fold increased risk of developing dementia with an HR of 2.59 and a 95% CI of 1.62-4.15. There was no association in the inflammatory markers for the development of dementia in these patients.  

The cohort study evaluated showed a variety of strengths. The researchers used the inflammatory markers data from baseline from all the patients with type 2 diabetes. All the patients included in the original cohort study were 65 years and older, limiting data manipulation. Other strengths were that this study was followed-up for years, and most patients participated in the 10-years follow-up. Some weaknesses found in this study include the dementia clinical evaluation in the 371 deaths.  Another limitation of this study is the misdiagnosis of dementia as depression or vice versa due to the similar clinical presentation. The study evaluated depression at baseline and in the follow-up at year four but did not assess the duration of depression.   

In conclusion, this cohort study showed a relationship between depression in patients with type 2 diabetes and the incidence of dementia, with a risk of a 2.5-fold increase in these patients versus patients with no depression. The researchers conclude that there is no association between the inflammatory markers and the incidence of dementia in this group of patients. After evaluating this cohort study, it is vital to identify, diagnose, and treat depression in patients who have been diagnosed with type 2 diabetes to prevent dementia in older adults.  

Practice Pearls:  

• Patients with dementia who have been previously diagnosed with type 2 diabetes have a 2.5-fold increased risk of developing dementia.  
• An increase in inflammatory cytokines is not a definite marker for this association. 
• Diagnosis and treatment of depression in patients previously diagnosed with type 2 diabetes are vital for managing dementia risk.  

Diabetes and Depression: Coping with the Two Conditions. Diabetologia Sept. 3, 2020,  

 Carr, Alistair L et al. “Depression as a risk factor for dementia in older people with type 2 diabetes and the mediating effect of inflammation.” Diabetologia vol. 64,2 (2021): 448-457.  

  Katon, Wayne et al. “Effect of depression and diabetes mellitus on the risk for dementia: a national population-based cohort study.” JAMA psychiatry  

Laura Martínez López, PharmD. Candidate 2021, Lake Erie College of Osteopathic Medicine, College of Pharmacy