David Levy, MD, FRCP
Associations with depression in type 2 diabetes
In the Look AHEAD study, about 15% had symptoms of mild–moderate depression, about 17% were current users of antidepressant medication, and about 4% both . Other studies in the USA have described higher rates, up to 25%, of more severe depression, with all ethnic groups (white, African-American, Latinos and others) recording similar rates. Not surprisingly, depression in diabetes is associated with non-adherence to diabetes self-care (this applies to type 1 as well); although a wide variety of behaviors has been studied (including diet, medication and glucose monitoring), the most consistent association is with missed medical appointments, and impaired interpersonal functioning in depressed people may be an important mediator of this behavior. Once again, there is difficulty in ascribing a causal association (though it might seem self- evident) between depression and impaired diabetes self-care, never mind a direction of causality, but a longitudinal study found that worsening levels of self-care and depression were associated with baseline depression in type 2 diabetes.
In Look AHEAD, depression scores and use of antidepressant medication were independently associated with:
- hypertension and use of antihypertensive medication;
- current smoking;
- lower peak exercise activity.
Again, the management corollary of these unspectacular findings is important: identification of clusters of these factors should be an alert to the presence of depression. In established neuropathy, neurological disability predicts increased depressive symptoms; slightly more counter-intuitively, depression was most strongly linked with the symptom of unsteadiness, an important factor limiting a wide spectrum of activities and resulting in diminished self-worth.
There are clearly barriers to identifying depression in those who are most likely to suffer it, namely those with more chronic complications. Biomedical priorities and targets steer the time-limited agenda of a medical consultation, and in primary care (and possibly even more likely in secondary care) the greater the number of medical comorbidities, the less likely depression will be recognized.
Interventions in depression in type 2 diabetes
Many psychological interventions have been described (especially group cognitive behavior therapy, but also stress management, relaxation therapy and individual cognitive behavior therapy). A meta-analysis of 12 trials that measured HbA1c over a period of usually up to 6 months found that intervention was associated with a significant fall in HbA1c of 0.76%, but it was not possible to determine which intervention method was most successful nor how the various treatments exerted their effect. Psychological treatments seem to be of real value, and about twice as effective as antidepressants in inducing remission in a major depressive illness, though long-term effects are not known . Inevitably, not all studies have found that glycemic control improved with even enhanced antidepressant therapy (psychological or pharmacological), but improved glucose control cannot reasonably be required to be a primary outcome of a therapy intended to alleviate a psychological problem. There is a hint that interventions designed to manage depressive symptoms may be more effective in improving self-care than those that reduce distress. Patients report a high degree of satisfaction (60–80%) with all modalities of treatment (antidepressants, mental health provider, alternative healers) .
In the short-term, antidepressant treatment (e.g. tricyclics, SSRIs and SNRIs) is reasonably effective, but increases the likelihood of recovery from the index episode of depression by only 20–30%; sertraline has no effect beyond placebo in those over 55 years old, and those with higher pain scores had a particularly poor response. The long-term outlook is poor. Fewer than 50% of patients remained well in the year after treatment, about 15% develop chronic depression resistant to current treatments, a high proportion relapse as often as once a year, and very few remain free of depression in the following 5 years. Depression treated with antidepressants seems to correspond reasonably well with glycemia, improving with treatment and deteriorating with relapse, and maintenance antidepressant treatment is more effective than placebo in deferring relapse.
The important Pathway study (2006) found that patients (nearly all type 2) with two or more chronic complications of diabetes benefited over a year with a comprehensive depression care pathway compared with usual care. The intervention was intensive, involving primary care physicians, nurse specialists in depression management, and an initial strategy (according to patients’ wishes) of either antidepressant therapy or sessions of problem-solving therapy. Routine and intensive input were equally effective in those with fewer complications, but patients with one or more macrovascular complications seemed to do especially well . The forthcoming TEAMcare study will further explore a comprehensive biopsychosocial intervention programme in patients with depression, and poor diabetes control with or without coronary heart disease.
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