Association between depression and concurrent Type 2 diabetes outcomes varies by diabetes regimen

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Abstract
Aims Although depression has weak associations with several Type 2 diabetes mellitus (DM) outcomes, it is possible that these associations are concentrated within certain patient subgroups that are more vulnerable to their effects. This study tested the hypothesis that depression is related to glycaemic control and diabetes‐related quality of life (DQOL) in patients who are prescribed injected insulin, but not those on oral glucose‐lowering agents alone. Methods Participants (103 on insulin, 155 on oral glucose‐lowering agents alone) with Type 2 DM were recruited from a large US healthcare system and underwent assessment of glycaemic control (glycated haemoglobin; HbA1c), medication adherence and diabetes self‐care behaviours, DQOL and depression (none, mild, moderate/severe). Results There was a significant regimen × depression interaction on HbA1c (P = 0.002), such that depression was associated with HbA1c in patients using insulin (β = 0.35, P < 0.001) but not in patients using oral agents alone (β = –0.08, P = NS). There was a similar interaction when quality of life was analysed as an outcome (P = 0.002). Neither effect was mediated by regimen adherence. Conclusions The generally weak association between depression and glycaemic control is concentrated among patients who are prescribed insulin. Similarly, the association between depression and illness quality of life is strongest in patients prescribed insulin. Because this is not attributable to depression‐related adherence problems, psychophysiological mechanisms unique to this group ought to be carefully investigated. Clinicians might be especially vigilant for depression in Type 2 DM patients who use insulin and consider its potential impact upon their illness course.