Both diabetes and clinical depression are known to be risk factors for dementia. Now a study that tracked nearly 4000 diabetics over 5 years has found having both increased the risk 2.7-fold. Nearly 8% of the diabetics with major depression (36 of 455) developed dementia over the five years, compared to 4.8% of those with diabetes alone (163 of 3382). Those who developed dementia within 2 years of being diagnosed with depression were excluded. Depression is common among people who have diabetes.
(2010). Comorbid Depression Is Associated with an Increased Risk of Dementia Diagnosis in Patients with Diabetes: A Prospective Cohort Study.
Journal of General Internal Medicine. 25(5), 423 - 429.