RESUMO
BACKGROUND: Treating comorbid depression does not always improve outcomes for people with type 2 diabetes. Evidence is lacking on potential psychological and behavioural intermediaries of the impact of depression on diabetes outcomes. OBJECTIVE: To synthesise evidence on the impact of comorbid depression on self-efficacy, illness perceptions, and self-management in people with type 2 diabetes. DATA SOURCES: We searched PubMed, Embase, PsycINFO, and Global Health databases from inception up to 29th March 2023. STUDY ELIGIBILITY CRITERIA: Only prospective studies (cohort or intervention studies) were included, with no restrictions on language. The outcomes were self-efficacy, illness perceptions, and self-management. PARTICIPANTS: People with type 2 diabetes in community or health settings. EXPOSURE: Comorbid depression or depressive symptoms in people with type 2 diabetes. SYNTHESIS OF RESULTS: A narrative review of heterogeneous studies. RISK OF BIAS: The risk of bias was assessed using the Effective Public Health Practice Project (EPHPP) quality assessment tool for quantitative studies. RESULTS: Twenty-five studies were included, all from high-income countries. Depression was associated with lower self-efficacy (2 studies), poor illness perception (1 study), and poor self-management practices (17 studies) in people with type 2 diabetes. In 6/7 studies, depressive symptoms predicted less adherence to dietary recommendations, 8/10 studies found depressive symptoms were associated with poor medication adherence, 1/3 study found that depressive symptoms were associated with poor weight control, 3/4 with less physical exercise, and 2/3 with general self-care practices. LIMITATIONS: There were no studies from low- and middle-income countries and non-Western settings, and we cannot assume the mechanisms linking comorbid depression with diabetes outcomes are similar. CONCLUSIONS: Comorbid depression was associated with lower self-efficacy, poorer self-management, and less adaptive illness perceptions among people with diabetes.