David Levy, MD, FRCP
Type 2 diabetes
Much of the literature concerns the important problem of type 2 diabetes and depression and, in comparison with type 1 diabetes, little about the psychological disturbances associated with specific phases of type 2 diabetes. However, we are entering an important phase of research in which detailed and validated measures of psychological function are being incorporated into large-scale longitudinal studies investigating earlier phases of diabetes (e.g. Look AHEAD, Diabetes Prevention Program) with much more reliable quantitative outcome data.
Causal link between depression and type 2 diabetes
There has been much debate over whether type 2 diabetes causes depression or, more intriguingly, whether the reverse applies. Until recently the bidirectionality was appreciated but there was no strong evidence to support one model over the other (Table 13.1). Several meta-analyses of longitudinal studies have now concluded that there is a stronger link between baseline depression and incident type 2 diabetes than vice versa (about 40–60% increased risk in the former direction compared with about 15–20% in the latter) . In the period leading up to the diagnosis of type 2 diabetes, patients were twice as likely to be taking antidepressants as control subjects. This finding, that depression itself is a risk factor for the development of type 2 diabetes, is partly, but only partly, supported by the Diabetes Prevention Program (see Chapter 1), in which the diagnosis of diabetes was precisely defined. Elevated depression scores at study entry were not associated with the progression of IGT to diabetes, but in the intensive lifestyle and placebo metformin groups, baseline antidepressant use and continuous antidepressant use during the study was associated with a marked (2–3.5-fold) increased risk of developing diabetes, independent of other risk factors. This suggests that antidepressants themselves may contribute to the development of diabetes, and that metformin treatment prevents it. However, it may be that more severe depression, for which antidepressant use is a marker, is associated with developing diabetes, as found in the meta-analysis . Details apart, the message for clinicians is that diagnosed and treated depression are strong risk factors for diabetes. The diagnosis of type 2 diabetes does not appear to have a severe psychological impact, other than short-lived anxiety, and a transient rise in the use of antidepressant medication in the year after diagnosis.
Other emotional problems in type 2 diabetes
Emerging after diagnosis, generalized anxiety disorder is common in type 2 (and type 1) diabetes, estimated at about 40% in both conditions, significantly more frequent in women. The relationship between anxiety and poor glycemic control is statistically significant. Diabetes- specific emotional problems are common (notably worry about the future, the possibility of serious complications, guilt or anxiety when straying from recommendations about management, and concern that mood or feelings are related to blood glucose levels). These concerns, particularly perception of disease severity and worry about the burden of self-care, are more common among insulin-treated patients than in non- insulin-treated patients, but there are no differences between tablet- and diet-treated patients. It will be interesting to see what impact the concerns about insulin treatment itself have in comparison with the new injected GLP-1 analogues. The prevalence of diabetes-specific distress increases with severity of depression.
There is a disconnection between the frequently reported improvement in quality of life seen with insulin treatment in type 2 diabetes and the finding that patients report greater distress with insulin treatment than with either diet alone or oral hypoglycemic agents. The difference is explained by the improvement in symptoms with initiating insulin treatment compared with the long-term distress of insulin-treated patients. However, much of the difference is explained by more advanced disease associated with insulin treatment and greater expected burden of self- care. Nevertheless, other treatment modalities carry their own sources of distress, especially acceptance of the condition in those treated with diet and oral hypoglycemic agents; diet-treated patients are distressed by unclear management goals .
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