A report quantified the effects of comorbid depression and diabetes on mortality from cancer and on other causes of death not including circulatory disease. A prospective cohort study included 499,830 people, who were 40 to 69 years old at baseline and enrolled at any of 22 UK sites during 2006-2010 with follow-up by linkage to national datasets.
The risks of all-cause mortality, death due to cancer, and death from other causes each exceeded the sum of the risks due to diabetes and depression alone, suggesting an interaction on the additive scale. However, statistical evidence of an additive interaction only existed for all-cause and cancer mortality. The synergistic effect of depression on all-cause mortality exceeded the expected additive effect due to either disorder alone and was largely driven by cancer and by causes other than circulatory disease and cancer.
People with depression and diabetes are at an increased risk for all-cause death, including death due to cancer, circulatory disease, or other causes. Depression and diabetes appeared to act synergistically in their effect on all-cause mortality even after adjustment for potential confounders. The combined effect on death appears largely driven by cancer and other causes but not by circulatory diseases.