A well-developed literature has investigated the comorbidity between Type 1 diabetes mellitus and depression, and the relationship of depression to medical outcomes among those with Type 1 diabetes mellitus. It has been shown that individuals with diabetes mellitus have a disproportionately higher rate of psychiatric disorders, with affective and anxiety disorders being more commonly diagnosed than in the general population. In one study of Type 1 diabetes mellitus and type 2 (type 2 diabetes mellitus) inpatients, 52% presented with at least one lifetime psychiatric disorder, and 41.3% presented with a diagnosis within the past 6 months. In this sample, affective and anxiety disorders represented 83% of the psychiatric diagnoses. Another study of Type 1 diabetes mellitus outpatients showed rates of anxiety and depressive disorders at 44% and 41.5%, respectively.
Some individual studies have found that depression among those diagnosed with diabetes was vastly elevated, compared to the individuals without diabetes, with depression as high as six times higher for those with diabetes mellitus. In an epidemiological study of depression in individuals with Type 1 diabetes mellitus and type 2 diabetes mellitus, findings revealed that depression was three to four times more prevalent in this population than in the general population. These results suggest that 15% to 20%, or approximately one in five individuals with either Type 1 diabetes mellitus or type 2 diabetes mellitus are afflicted with depression. Furthermore, approximately 40% of individuals with diabetes mellitus have significantly elevated levels of depressive symptomatology, but are not clinically depressed.
The literature has developed enough to permit meta-analytic studies. Taken together, the evidence from 42 studies regarding rates of depression among those with Type 1 diabetes mellitus or type 2 diabetes mellitus indicates a 2.0 odds ratio for depression among those with diabetes. While these studies include both Type 1 diabetes mellitus and type 2 diabetes mellitus populations, the data did not suggest a difference between Type 1 diabetes mellitus and type 2 diabetes mellitus. For those with Type 1 diabetes mellitus, there appeared to be twice the rate of depression as among those without diabetes. There were, however, differences related to gender. Rates of depression were 28% among women with diabetes, and 18% among men with diabetes, but due to different base rates for depression among men and women without diabetes, the 2.0 odds ratio was consistent for both genders. A more recent review, investigating depression among only samples with Type 1 diabetes mellitus, and including rive additional studies since the Anderson and colleagues study, reported that 12% of those with Type 1 diabetes mellitus exhibited comorbid depression, compared with only 3.2% of the comparison group without diabetes. These data suggest that, among individuals with Type 1 diabetes mellitus, the rates of depression may be above three times the rate as those without diabetes mellitus. Indeed, 27% of children and adolescents diagnosed with Type 1 diabetes mellitus developed a major depressive episode during the 10 years after the diagnosis of Type 1 diabetes mellitus. These series of studies and the resulting meta-analytic reviews demonstrate that regardless of the exact degree of increased risk and prevalence, depression appears elevated in prevalence among those with Type 1 diabetes mellitus.
Given the elevated prevalence of depression among individuals with diabetes mellitus, a few studies have attempted to characterize the disorder further. In a study by Peyrot and Rubin, elevated depressive symptoms varied according to two factors: (/) nondiabetes specific (generic) factors and (//) diabetes-related factors. The researchers found higher rates of depression among women, individuals who were unmarried, and those with less education. Higher rates of depression were also found in individuals with three or more medical complications secondary to their diabetes (i.e., retinopathy, neuropathy, kidney disease, etc). Other studies have examined the relationship between social problems and depression in individuals with diabetes mellitus. Roy found that social problems are reported more often among individuals with Type 1 diabetes mellitus. Wilkinson and colleagues found that individuals reporting major social problems had significantly higher levels of psychiatric morbidity.
Relationship of Depression to Medical Outcomes
Of further concern is the relationship between comorbid depression and medical outcomes among those with Type 1 diabetes mellitus. Several studies have investigated the influence of depression on glycemic control and other adherence measures. Studies have found that individuals with diabetes mellitus and a history of depression showed significantly worse glycemic control as measured by glycosylated hemoglobin. Additionally, afew meta-analytic studies now exist and have shown a significant relationship between depression and poorer metabolic control among those with both Type 1 diabetes mellitus and type 2 diabetes mellitus. Not surprisingly, depression has also shown a relationship to greater complications of persistent hyperglycemia. Inquiry continues regarding the exact nature of this relationship between depression and hyperglycemia. One study sought to determine whether depression induced a decrease in diabetes self-care and whether changes in self-management mediated the relationship between depression and hyperglycemia. Although the inclusion of the score from the summary of diabetes self-care activities in regression analyses attenuated the relationship between depression and glycosylated hemoglobin among individuals with Type 1 diabetes mellitus, it did not account for a significant mediation of the depression -> hyperglycemia relationship. As such, continued investigation of this relationship is necessary, to determine the strength of the depression -> reduced self-management -> hyperglycemia mechanism, or evaluate other psychological and psychophysiological mechanisms for this relationship.
The course of depression in the diabetes mellitus population is chronic and severe, and the presence of depression in individuals with diabetes mellitus may significantly worsen the course of both disorders. There is sufficient data in the literature demonstrating the (0 increased prevalence of depression in the Type 1 diabetes mellitus population, (ii) deleterious impact of depression on medical outcomes, and (Hi) evidence that effective treatments exist. However, depression continues to be underdiagnosed and undertreated. In a study of nine primary care practices, 49% of patients with a diagnosis of either Type 1 diabetes mellitus or type 2 diabetes mellitus, reporting clinically significant depression in a systematic screening, were not diagnosed or treated. Only 43% of those patients who were appropriately diagnosed with depression were receiving antidepressant pharmacotherapy, and only 6.7% received four or more psychotherapy sessions during the previous year. This suggests that not only were many patients with depression not initially diagnosed, but those who were diagnosed were not adequately treated.
Treatment for Comorbid Depression and Diabetes
A few studies have examined the influence of psychopharmacology and psychotherapy on the treatment of depression in this population; however data remain scarce. Although the prevalence of major depression and diabetes is well established, there are no large-scale, randomized controlled clinical trials. Both antidepressant medications and cognitive behavioral therapy have demonstrated short-term effectiveness in the treatment of depression among diabetes mellitus individuals. The results seem promising with improvement towards a reduction in depressive symptoms, as well as improved glycemic control. As previously stated, data is available showing that depression has been shown to worsen medical outcomes for those with diabetes. Many of the treatment data for depression and diabetes show improvements in medical outcomes (i.e., improved metabolic control); however, depression treatment for those with comorbid depression and diabetes have not consistently shown improvement in patients’ self-management or glycemic control.
Pharmacological management of depression may be necessary for long-term or resistant depressive symptoms. Monoamine oxidize inhibitors and tricyclic antide-pressants are not commonly used to treat depression in persons with diabetes due to potential adverse side effects (e.g., short-term hyperglycemia, hypoglycemic unawareness, postural hypotension). Notably, a randomized clinical trial of nortriptyline revealed significant reductions in depression; however, there was an adverse effect on glucose control. Selective serotonin reuptake inhibitors appear to be the preferred antidepressant of choice for those with diabetes mellitus. However, Selective serotonin reuptake inhibitors are not without side effects. This class of drugs may alter the metabolism of certain oral hypoglycemics and certain drugs can be associated with weight gain. Effectiveness data suggest that Selective serotonin reuptake inhibitors are associated with both improved depressive symptoms and metabolic control. The SSRI, fluoxetine, has been evaluated for its efficacy on reducing depressive symptoms in both Type 1 diabetes mellitus and type 2 diabetes mellitus patients. An 8-week, randomized clinical trial found that fluoxetine significantly reduced depressive symptoms compared to placebo and trended towards better glycemic control.
Lack of statistical power is an important note of caution in interpreting the data on antidepressants on depressive symptoms in persons with diabetes. Most of the pharmacotherapy studies have too few participants to robustly measure symptom reduction and symptom burden from diabetes, and no long-term data are available.
Cognitive behavioral treatment has been shown useful in the treatment of depression in persons with diabetes; however, data is scant. This therapeutic approach modifies dysfunctional thinking, reduces negative emotions, trains stress reduction, and provides skill building in areas of deficit. Improvements in mood, quality of life, and coping were demonstrated in the only large-scale randomized clinical trial to date in type 2 diabetes mellitus adults. However, other data from less statistically robust studies exists. Cognitive behavioral therapy has shown effects through improved glycemic control and quality of life, and evidence suggests that cognitive-behavioral therapies techniques may prove beneficial in improving compliance to diabetes regimen.
Combined treatment of pharmacotherapy and psychotherapy has been found to be significantly more efficacious in reducing depressive symptoms than placebo alone .
Overall, with the limited data available, it appears that both psychopharmacological and psychotherapeutic approaches have beneficial effects on depression reduction in persons with diabetes, and may promote improvement in medical outcomes.