April Bonus Edition 2005
Discussion of the relationship between glucose metabolism and psychiatric illness has occurred for at least three centuries. The eminent English physician Thomas Willis, M.D., first documented an interaction between psychiatric illness and diabetes mellitus (DM) in the late-17th century. Willis, who coined the term diabetes mellitus, made the following statement: "Sadness, or long sorrow, as likewise convulsions, and other depressions and disorders of the animal spirits, are used to generate or foment this morbid disposition."
Diabetes mellitus is a common, chronic condition affecting approximately 6.3% of the population (Centers for Disease Control and Prevention, 2003). Rather than a single disease entity, DM is a group of metabolic illnesses with hyperglycemia as the central feature. It is important to distinguish between type 1 and type 2 DM. Type 1 DM, formerly called insulin-dependent DM, is a juvenile-onset disease involving autoimmune destruction of insulin-secreting pancreatic b cells. Type 2 DM, formerly called non-insulin-dependent DM, is an adult-onset disorder that begins with resistance to the effects of insulin. Age, obesity and lack of physical activity are major risk factors for type 2 DM, and there is a strong genetic predisposition to the illness. Approximately 90% to 95% of individuals with diabetes have type 2 DM (American Diabetes Association [ADA], 2004).
Epidemiology and Pathophysiology
Multiple investigators have studied the relationship between depression and DM. Although published reports vary by method of diagnosing depression and reported prevalence of depression in DM, Anderson et al. (2001) completed a comprehensive meta-analysis of 42 studies demonstrating that the presence of diabetes consistently doubles the odds of comorbid depression. Furthermore, when depression and diabetes coexist, the severity of diabetes increases. A meta-analysis demonstrated the association of depression with hyperglycemia (Lustman et al., 2000a), as well as diabetic complications including retinopathy, nephropathy, neuropathy, sexual dysfunction and macrovascular disease (de Groot et al., 2001). Black et al. (2003) found additionally that comorbid depression predicts greater mortality in patients with type 2 DM.
This relationship may not be unique to unipolar depression. Most studies of depression and DM do not distinguish between unipolar and bipolar depression. Several reports show that hospitalized patients with bipolar disorder also have increased rates of diabetes compared to general populations (Cassidy et al., 1999; Lilliker, 1980; Regenold et al., 2002). These studies have been criticized, however, for the potential ascertainment bias inherent in studying a sample of hospitalized patients whose frequent contact with health care professionals may increase their chance for diabetes diagnosis.