A literature review of data, published in Systematic Reviews, identified a need for further research on the relationship between subthreshold depression and self-care behaviors in adults with type 2 diabetes. The investigators found that results were generally inconsistent and vulnerable to bias.

Researchers performed a systematic review of the MEDLINE, EMBASE, PsycINFO, Emcare, and CINAHL databases for any observational studies of subthreshold depression in adults (≥18 years) with type 2 diabetes. Specifically, they assessed the effect of depression on diabetes self-care behaviors, including healthy eating, consistent physical activity, blood glucose monitoring, medication adherence, abstinence from smoking, and foot care.

Subthreshold depression was defined as the presence of depressive symptoms that did not meet the diagnostic criteria for major depressive disorder. Data were extracted by 2 independent reviewers, and disagreements were adjudicated by a third author. Extracted data included participant demographic and clinical characteristics, study setting, country of study, metric for subthreshold depression, and measures of self-care. Methodological quality was assessed using the Joanna Briggs Institute (JBI) Critical Appraisal Checklist tool.

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A total of 6408 articles were identified through database screening. However, after full-text review on 47 studies, only 2 met full eligibility criteria. Both studies were hospital-based; 1 was longitudinal and 1 was cross-sectional. The longitudinal cohort comprised 866 primary care outpatients in Germany; the cross-sectional study included 103 outpatients in the United States.

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In the longitudinal study, patients were classified as having subthreshold depression if they had a Depression Screening Questionnaire score between 5 and 7. In the cross-sectional study, a score ≥3 on the Patient Health Questionnaire and diagnosis by a study clinician was considered subthreshold depression. Self-care behaviors were measured by questionnaires in both studies, although only the cross-sectional study used a validated measure.

The 2 studies reported conflicting results. In the longitudinal study, subthreshold depression was associated with nonadherence to self-care behaviors over the course of 12 months of follow-up (P <.001). The relationship remained after adjustments for relevant covariates, including body mass index, smoking, duration of diabetes, and diabetes treatment. The cross-sectional study found that patients with subthreshold depression scored numerically lower on self-care behaviors. However, the association was not significant. Per the JBI checklist, both studies displayed potential sources of bias, including small sample size, lack of use of a validated depression measure, and poor adjustment for confounders.

Although this study represents the first review to examine the literature on subthreshold depression and self-care in diabetes, conflicting results and risk for bias prevent any precise conclusions. Further study is necessary to assess the relationship between sub-clinical depression and self-management in type 2 diabetes.


Shrestha M, Ng A, Al-Ghareeb A, Alenazi F, Gray R. Association between subthreshold depression and self-care behaviors in people with type 2 diabetes: a systematic review of observational studies. Syst Rev. 2020;9(1):45.