Evidence-Based Reviews

The link between schizophrenia and diabetes

Author and Disclosure Information

Vigilant metabolic monitoring informs treatment decisions



Discuss this article at www.facebook.com/CurrentPsychiatry

Although diabetes and schizophrenia are common companions, it is unclear how this association should influence our practice. What do we need to know about diabetes, and what are the key intervention points for psychiatrists?

This article is informed by my experience monitoring >1,000 patients with schizophrenia in a large urban mental health facility using an electronic metabolic monitoring system and consulting on hundreds of individuals with comorbid schizophrenia and diabetes in a mental health metabolic clinic.

A significant link

The association between schizophrenia and diabetes has been recognized for more than a century.1 The prevalence of diabetes is increased 2- to 3-fold in patients with schizophrenia.2,3 This relationship is specific to type 2 diabetes mellitus (T2DM); type 1 diabetes mellitus, an autoimmune disease, is less common in patients with schizophrenia.4 Factors that contribute to comorbidity between schizophrenia and T2DM include:

  • illness susceptibility: the mechanisms remain unclear but include the thrifty phenotype hypothesis,5 autonomic hyperactivity,6 and potential cellular and genetic links7,8
  • lifestyle: diet, physical inactivity, and cigarette smoking9-12
  • antipsychotic use13
  • social health determinants, such as income, housing, and food insecurity.14
The relative contribution of factors underlying this association is unknown; it is likely that they all contribute. Nevertheless, based on information from our facility’s metabolic monitoring database, depending on demographic variables, such as ethnicity and cigarette smoking, 20% to 30% of patients with schizophrenia will develop diabetes or prediabetes during the course of psychiatric treatment.

When evaluating a patient’s risk for a cardiac event, we consider having a diabetes diagnosis equivalent to having had a myocardial infarction.15 Likely, the high prevalence of T2DM among schizophrenia patients and challenges in managing diabetes and prediabetes underlies these patients’ reduced life expectancy.16 Self-care, a cornerstone of diabetes management, is challenging for patients with schizophrenia because of deficits in executive functioning, working memory, and motivation, coupled with negative symptoms and social and economic disadvantages that often accompany schizophrenia.

How diabetes impacts practice

What psychiatrists need to know. Insulin resistance—reduced biologic effectiveness of insulin—is the precursor of T2DM. Insulin is required to move glucose from the blood into cells. Weight gain, particularly abdominal adiposity, is the principal driver of insulin resistance. The body responds by producing more insulin (hyperinsulinemia) to maintain glucose homeostasis. Hyperinsulinemia underlies metabolic syndrome, an important risk marker for developing T2DM. Diabetes usually develops after many years when the pancreas fails to compensate for insulin resistance.

In most cases the development of diabetes in patients with schizophrenia follows this course. Weight gain, a consequence of lifestyle factors as well as antipsychotics and other psychotropics that promote obesity, leads to progressive insulin resistance. Consequently, metabolic syndrome is twice as prevalent among patients with schizophrenia compared with matched controls.17,18

Occasionally patients develop T2DM within a few weeks or months of starting antipsychotic treatment—usually with clozapine or olanzapine—before they gain weight, which suggests a second mechanism may be involved. Animal studies have documented rapid development of insulin resistance after a single subcutaneous injection of antipsychotics that have high metabolic liability, possibly through a direct effect on insulin signaling.19 This phenomenon has been difficult to demonstrate in humans.20

Psychiatrists need to know how to diagnose diabetes (Table 1)21-23 and the signs and symptoms of diabetes and diabetic ketoacidosis (Table 2).24,25 Hemoglobin A1C diagnostic testing often is the preferred test because it does not require fasting.

Managing diabetes is complex and ideally involves a range of health practitioners who work with patients to provide education, promote self-care behaviors, and direct complex health care. These services are outside the scope of psychiatric practice, but given the functional deficits in seriously mentally ill patients, it is important to have an overview of diabetes care (Table 3).

In addition to diagnosing diabetes, psychiatrists should be able to identify patients at risk for developing diabetes and initiate prevention strategies. Interventions are focused on lifestyle—weight reduction, increased physical activity, diet, and smoking cessation—as well as pharmacologic strategies such as metformin.

Diagnostic criteria and strategies to manage prediabetes and metabolic syndrome are outlined in Table 4.21,26,27 Prediabetes and metabolic syndrome predict development of T2DM. Additional risk factors include ethnicity (Hispanic, black, Native American, and South Asian), family history, gestational diabetes, and cigarette smoking.28

What patients need to know. Similar to schizophrenia, a diabetes diagnosis may be difficult for patients to accept. Initially, a patient may have no manifestations or symptoms. However, untreated diabetes has serious long-term health consequences—including blindness, amputations, kidney disease, and early death from heart attacks.

Next Article: