• Heart Failure
  • Cardiovascular Clinical Consult
  • Adult Immunization
  • Hepatic Disease
  • Rare Disorders
  • Pediatric Immunization
  • Implementing The Topcon Ocular Telehealth Platform
  • Weight Management
  • Monkeypox
  • Guidelines
  • Men's Health
  • Psychiatry
  • Allergy
  • Nutrition
  • Women's Health
  • Cardiology
  • Substance Use
  • Pediatrics
  • Kidney Disease
  • Genetics
  • Complimentary & Alternative Medicine
  • Dermatology
  • Endocrinology
  • Oral Medicine
  • Otorhinolaryngologic Diseases
  • Pain
  • Gastrointestinal Disorders
  • Geriatrics
  • Infection
  • Musculoskeletal Disorders
  • Obesity
  • Rheumatology
  • Technology
  • Cancer
  • Nephrology
  • Anemia
  • Neurology
  • Pulmonology

Diabetes and Mental Illness: Factors to Keep in Mind


Persons with severe mental illnesses (SMI), such as schizophrenia, are at increased risk for comorbid conditions- including type 2 diabetes-independent of therapy. SMI sufferers especially at risk for type 2 diabetes are women, African Americans, and persons older than 45 years. Among the possible causes of increased susceptibility to type 2 diabetes are such schizophrenia-associated conditions as impaired glucose tolerance, overweight, obesity, inadequate nutrition, lack of exercise, and inadequate self-care. Other obstacles to good health care among patients with schizophrenia include impaired communication ability, denial of illness, social withdrawal, and undertreatment because of comorbid conditions. Different antipsychotic medications may also contribute to preexisting insulin resistance or glucose intolerance. Clinicians can optimize care by understanding the most significant barriers for each patient and incorporating this knowledge into an active treatment plan.


Persons with severe mental illness (SMI) (eg, schizophrenia) are at higher risk for medical comorbidities than those in the general population. The presence of SMI affects mortality as well as morbidity. The life span of men with schizophrenia is approximately 10 years shorter than that of men who do not have schizophrenia, while women with schizophrenia live an average of 9 years fewer than normal.1

Explanations for this higher likelihood of coexisting medical conditions and decreased average life span in persons with schizophrenia have focused on the ways schizophrenia or its treatments may predispose patients to greater incidence and severity of medical illness. For example, schizophrenia has been associated with reduced pain sensitivity, a phenomenon that can be exacerbated by antipsychotic agents routinely prescribed for persons with schizophrenia. During the acute phases, schizophrenia may cause patients to misinterpret or deny symptoms of illness. Patients who are socially withdrawn may be reluctant to seek medical care. If they do seek care, physicians may sometimes find it difficult to evaluate these patients appropriately because of their communication and cognitive difficulties. Poor health habits-including smoking, physical inactivity, and an unhealthful diet-may contribute to increased morbidity and mortality. Antipsychotic medications can cause weight gain, elevated serum glucose levels, movement abnormalities, and an apathetic state that intensifies social isolation and self-neglect.

In this article, we address a number of factors-including diabetes and obstacles to appropriate medical care- that increase the health burden of patients with SMI.


As early as the 1950s and 1960s, research findings had suggested that persons who have schizophrenia are at increased risk for type 2 diabetes.2-6 The work of the Schizophrenia Patient Outcomes Research Team (PORT) provides evidence of this association.7-12 In a 3-part study, the researchers found a remarkably consistent prevalence of type 2 diabetes in several clinical samples that used both direct interview and claims data (Table).

The first part of the study was a systematic field survey of 719 persons with schizophrenia in a variety of treatment settings and locations. One hundred seven patients (14.9%) reported having ever been told by a physician that they had diabetes. Seventy-eight of those patients (72.9%) currently had diabetes; of this group, 67 (85.9%) were being treated for it.

In the second part of the study, researchers accessed a database of all patients with a paid Medicaid claim for schizophrenia in a single state in 1990. The sample included 6066 persons who had a diagnosis of schizophrenia on a Medicaid claim in 1991, were not also enrolled in Medicare, and had a consecutive year of coverage. Six hundred sixty-one patients (10.9%) had an outpatient diagnosis of diabetes, and 130 (2.1%) had an inpatient diagnosis. Six hundred seventy-three patients (11.1%) had any diabetes diagnosis.

The third part of the study analyzed Medicare claims among a group of persons that included a random sample (5%) of all patients in the United States with a paid claim for diagnosis of schizophrenia in 1991. Of the 16,480 patients, 11,447 were between the ages of 18 and 64 years. Nine hundred ninety-nine patients (8.7%) had an outpatient diagnosis of diabetes, and 204 (1.8%) had an inpatient diagnosis. A total of 1040 patients (9.1%) had a diagnosis of diabetes.

In all 3 parts of the study, persons with diabetes were significantly more likely to be women, African American, and older than 45 years. These risk factors for diabetes are similar to those observed in the general population.

The prevalence of diabetes in these samples ranged from approximately 9% to 15%. This compares with a prevalence of diabetes of 1.2% in persons aged 18 to 44 years and 6.3% in persons aged 45 to 64 years in the 1994 National Health Interview Survey.6

In a more recent study, investigators found that 10% of a group of 100 randomly selected patients receiving therapy for schizophrenia also had a diagnosis of diabetes. When compared with an age-, sex-, and race-matched group randomly identified from the National Health and Nutrition Examination Survey, persons with schizophrenia had an average risk of diabetes of about 2.07 (1.03 to 4.15) times greater than that of persons without schizophrenia (P < .04).

Other studies have shown that persons with schizophrenia are more likely to have a family history of non-insulin-dependent diabetes than persons who did not have schizophrenia (18% to 30% compared with 4.6%).13 (This correlation is not seen in the case of patients with schizophrenia who have insulin-dependent diabetes.14)

Schizophrenia has been associated with insulin resistance and impaired glucose tolerance,6,15-18 conditions that predispose to diabetes. Ryan and colleagues19 did a cross-sectional study comparing 26 first-episode drug-naive patients with schizophrenia to age- and sex-matched controls. The patients with schizophrenia were more likely to have impaired glucose tolerance and insulin resistance. In addition to causing weight gain, atypical antipsychotic drugs may also contribute directly to hyperglycemia.4,20,21 However, in a 1996 study of the prevalence of diabetes among 95 patients with schizophrenia, diabetes was not found to be related to antipsychotic drug use and was more common in patients not taking neuroleptics than in those who were taking them.3


Weight. Obesity and overweight are well-established risk factors for type 2 diabetes. For a number of reasons, persons with schizophrenia often have difficulty controlling their weight. A recent study compared the distributions of body mass index (BMI) and the prevalence of obesity and overweight among persons who did and did not have schizophrenia in nationally representative samples of the adult US population. The persons who had schizophrenia had significantly higher mean BMIs than those who did not.22 Among the causes of weight gain and obesity in persons with schizophrenia are inappropriate diet, lack of exercise, and the use of atypical antipsychotic medications.

One possible risk factor for obesity is the lack of proper nutrition. In a study of dietary and exercise habits of patients who have SMI, those with major affective disorder or schizophrenia had an elevated BMI (K.W. et al, unpublished data, 2001a). The mean BMI for the schizophrenia group was 29.6. According to the CDC, persons whose BMI is between 25 and 29.9 are considered overweight. Those with a BMI of 30 or higher are classified as obese and are likely to have health problems related to obesity. The mean for the schizophrenia group was in the overweight range, and a large proportion of the participants had BMIs that would classify them in the obese range. Therefore, it is likely that many of these patients would experience other medical problems in addition to their diabetes.

Dietary habits associated with poverty, unstable living situations, and frequent consumption of fast food and high-fat food can contribute to obesity.23 The diets of persons with schizophrenia often are higher in fat and lower in fiber than those of persons who do not have a mental illness. In a study that compared diet and exercise habits of persons with schizophrenia spectrum disorders and major affective disorders, 58% claimed that they had tried to lose weight within the past year (K.W. et al, unpublished data, 2001a). However, only 30% changed their eating habits during that time. Persons with SMI may not understand the connection between weight and diet. Even if they do understand it, they may not know how to improve their eating habits.

A lack of knowledge about nutrition and healthful food choices can contribute to poor eating habits. In a study of 291 patients with diabetes (K.W., unpublished data, 2002), participants who reported lower adherence to their diet had significantly higher levels of glycosylated hemoglobin (HbA1c) (P < .05). Those with greater perceived control of diet and exercise habits had lower levels of HbA1c than persons with less perceived control (F277 = 2.41, P < .01). Those with schizophrenia (F287 = 2.35, P < .10) were less likely to believe they could control their diabetes through diet and exercise than persons with no SMI diagnosis. Lack of knowledge about their illness and ability to control personal health outcomes may greatly confound the medical disorders of patients with schizophrenia.

Exercise. There is some evidence that lack of exercise can exacerbate weight-control problems in patients with schizophrenia. Although few data exist, it appears that these persons are less physically active than their mentally healthy counterparts. Many are sedentary.23 The reasons for this may include poverty, negative symptoms, institutionalization, and the sedative effects of some neuroleptics.

In a study of health behaviors and patterns among persons with SMI, patients reported that they believed they were less active than other persons their age (K.W. et al, unpublished data, 2001a). Persons with schizophrenia and persons with major affective disorders reported taking part in a number of exercise activities, such as walking a mile a day (50% vs 41%), jogging (7% vs 3%), biking (6% vs 12%), and swimming (5% vs 9%). Walking was the most popular form of activity, possibly because it is low cost and accessible. Patients may also need to walk because they lack transportation. This study suggests that outpatients may in fact have a reasonable foundation of activity on which to build an exercise program, but few currently exercise in a systematic, targeted manner.

In a study of persons with diabetes and mental illness, many participants (39%) reported exercising only 1 or 2 days a week (K.W. et al, unpublished data, 2001b). However, 51% of the participants responded "no" to the question, "Do you participate in a specific exercise session?" This demonstrates that many participants may walk or take part in activities but may need assistance in creating a plan or the opportunity for regular exercise.

Numerous studies have demonstrated the benefits of exercise in the general population.24 Physical fitness among persons with mental illness is often overlooked by clinicians, although poor physical fitness clearly affects these patients' health. The few existing studies of exercise programs for persons with mental illness suggest that exercise may be a safe, cost-effective intervention that confers both psychological and physiologic benefits.25,26

In a small interview survey of patients with schizophrenia who were randomly assigned to an aerobic or nonaerobic exercise program, most reported that exercise made them feel less depressed and anxious, raised their energy levels, and led to increased participation in other rehabilitation treatment modalities.26 Aerobic exercise was associated with superior results. Compared with patients in the nonaerobic program, those in the aerobic group had significantly decreased scores on the Beck Depression Inventory and significantly greater improvements in aerobic health. For example, these patients had an increase of 20.9% in their oxygen capacity after 12 weeks in the program. Although it is possible that such a large increase was the result of below-average fitness before the program, some patients in the aerobic group also lost significant amounts of weight (30 to 60 lb), which placed them in the normal range for their height and sex.

Pelham and colleagues26 interviewed 15 participants in their psychiatric rehabilitation program who did not participate in formal exercise therapies. The higher the level of aerobic fitness, the lower the level of depression observed. For persons with mental illness, exercise can provide a number of benefits similar to those in the general population. In addition, exercise can help prevent or decrease weight gain that is often seen in this population, thereby lowering the potential risk of diabetes.


Barriers to good care significantly affect the health status of persons with schizophrenia. These obstacles may be categorized as patient-related, health provider-related, or systems- related.

Patient-related barriers. A recent study showed that veterans with a psychiatric diagnosis sought medical care less frequently than other veterans.27 Specifically, patients with hypertension or diabetes and SMI had fewer medical visits than those with no psychiatric diagnosis. In a study of homeless persons with schizophrenia or depression, those with schizophrenia not only had fewer medical visits and documented medical complaints than those with depression, but they also were less likely to have had a careful physical examination and screenings for cholesterol levels and colon cancer (Figure).28

Some patients may be unable to clearly verbalize physical symptoms through an unfiltered psychotic thought process. In these cases, the clinician may find it difficult to differentiate a real symptom from a somatic delusion. Communication difficulties, dissatisfaction with treatment, fear, poverty, and denial or lack of insight can lead to nonadherence to treatment protocols, which affects both physical and mental health.

Another study of patients with schizophrenia in mental health treatment revealed different findings. Dickerson and colleagues29 compared the use of somatic health care services and perceived barriers to health care among patients with schizophrenia and affective disorders with published data from the general US population. Surprisingly, persons in both mental illness groups were more likely to have reported consulting a physician within the past year than the general US population (odds ratio [OR] for the schizophrenia group, 2.04 [1.26, 3.32]; OR for the affective disorder group, 2.37 [1.37, 4.09]). In this study, the comparison group was matched to the mentally ill group on sex, age, and race/ethnicity.

Does this study contradict the veterans study? It offers a different perspective. In the Dickerson study, the comparison group was matched to the mentally ill group on demographic parameters, not presence or severity of medical illness. The comparison group may have included persons with no illnesses. Greater illness or need in the mentally ill group may partially account for the findings. Still, this study suggests that persons receiving therapy for schizophrenia can access medical care with assistance. Whether the care received is comparable to that received by patients not mentally ill and whether the care is appropriate are unkown.

Dickerson and colleagues29 also noted that persons with SMI report high levels of perceived barriers in accessing health care. Fifty-nine percent of study patients-but only 19% of the general population-reported experiencing at least 1 barrier. These included transportation problems, not being able to get through on the telephone, not being able to get an appointment soon enough, and not being able to get to the clinician's office during regular hours. A number of factors that most people take for granted when accessing health care-such as effective verbal skills and access to telephones and transportation-may prevent persons with SMI from receiving the care they need.

Health provider-related barriers. Health care providers also may contribute to the problem of suboptimal care for patients with SMI. Clinicians may feel uncomfortable engaging patients who are actively psychotic, confused, or uncommunicative and may lack skills to interact with them effectively. They also may not take the extra time necessary to adequately assess a medical concern.

Some clinicians may manifest inappropriately stereotypical views. These clinicians may assume that the physical complaints of patients with SMI are "psychosomatic" and dismiss the patients without proper examination. Practitioners may find it difficult to take an accurate history of the presenting problem because of a patient's cognitive or memory impairment. In addition, inconsistent patterns of care may contribute to difficulties in tracking and treating the somatic illness.

Some psychiatrists are uncomfortable dealing with their patients' somatic problems, even though they may serve as these patients' "prin- cipal" physician. Persons with schizophrenia may avoid engaging with new physicians because of lack of knowledge about how to access new care, fear of being stigmatized, and lack of transportation.

Systems-related barriers. These include the dichotomy between general health care and mental health care delivery systems. Good integration of these areas is rare. This bifurcation fragments treatment and deters coordination and holistic care in a vulnerable population. Poverty and lack of health care coverage can be further barriers to adequate care in this population, as can limited service availability in some regions.

Another barrier to the treatment of a comorbid medical disorder may be the very phenomenon of comorbidity. An intriguing report by Redelmeier and associates30 studied the approximately 1.3 million residents of Ontario, Canada, who are 65 years or older. The nationalized health care system in Canada is one in which access should not be a problem. But researchers found that for 3 different pairs of unrelated medical disorders, treatment of the second disorder was less likely in the presence of the first. Patients with diabetes were 60% less likely than those without diabetes to receive treatment with estrogen replacement therapy. Patients with pulmonary emphysema were 31% less likely than those without pulmonary emphysema to receive lipid-lowering medication. Patients with psychotic syndromes were 41% less likely than those without psychotic syndromes to be treated for arthritis.

These results initially seem counterintuitive, since one might assume that a patient in this system would be treated for all of his or her complaints. There are numerous plausible explanations for this seeming discrepancy; however, the study powerfully suggests the potential for great undertreatment of comorbidity in the setting of chronic disease. Because schizophrenia is a chronic disease, such patients would be vulnerable to undertreatment for medical comorbidity in the same way as persons with other chronic illnesses.

Understanding the most significant barriers for each patient and incorporating this knowledge into active treatment planning can result in better access to medical care and reduced morbidity for persons with SMI.

1. Jeste DV, Gladsjo JA, Lindamer LA, Lacro JP. Medical comorbidity in schizophrenia. Schizophr Bull. 1996;22:413-430.

2. Felker B, Yazel JJ, Short D. Mortality and medical comorbidity among psychiatric patients: a review. Psychiatr Serv. 1996;47:1356-1363.

3. Mukherjee S, Decina P, Bocola V, et al. Diabetes mellitus in schizophrenic patients. Compr Psychiatry. 1996;37:68-73.

4. McKee HA, D'Arcy PF, Wilson PJ. Diabetes and schizophrenia-a preliminary study. J Clin Hosp Pharm. 1986;11:297-299.

5. Dynes JB. Diabetes in schizophrenia and diabetes in nonpsychotic medical patients. Dis Nerv Syst. 1969;30:341-344.

6. Richter D. Biochemical aspects of schizophrenia. In: Richter D, ed. Schizophrenia: Somatic Aspects. London: Pergamon Press; 1957.

7. Dixon L, Weiden PJ, Delahanty J, et al. Prevalence and correlates of diabetes in national schizophrenia samples. Schizophr Bull. 2000;26:903-912.

8. Adams PF, Marano MA. Current estimates from the National Health Interview Survey, 1994. National Center for Health Statistics. Vital Health Stat 10. 1995;10:193.

9. Cantor AB, Krischer JP, Cuthbertson DD, et al. Age and family relationship accentuate the risk of insulin-dependent diabetes mellitus (IDDM) in relatives of patients with IDDM. J Clin Endocrinol Metab. 1995;80:3739-3743.

10. Casparie A. Epidemiology of type II diabetes mellitus and ageing of the population: health policy implications and recommendations for epidemiological research. Int J Epidemiol. 1991;20(suppl 1): S25-S29.

11. Self-reported prevalence of diabetes among Hispanics-United States, 1994-1997. MMWR. 1999;48:8-12.

12. Harris MI. Diabetes in America: epidemiology and scope of the problem. Diabetes Care. 1998;21 (suppl 3):C11-C14.

13. Ryan MC, Thakore JH. Physical consequences of schizophrenia and its treatment: the metabolic syndrome. Life Sci. 2002;71: 239-257.

14. Finney GO. Juvenile onset diabetes and schizophrenia. Lancet. 1989;18:1214-1215.

15. Brambilla F, Guastalla A, Guerrini A, et al. Glucose-insulin metabolism in chronic schizophrenia. Dis Nerv Syst. 1976;37:98-103.

16. Holden RJ. The estrogen connection: the etiological relationship between diabetes, cancer, rheumatoid arthritis and psychiatric disorders. Med Hypotheses. 1995;45:169-189.

17. Holden RJ. Schizophrenia, suicide and the serotonin story. Med Hypotheses. 1995;44:379-391.

18. Holden RJ, Mooney PA. Schizophrenia is a diabetic brain state: an elucidation of impaired neurometabolism. Med Hypotheses. 1994;43:420-435.

19. Ryan MC, Collins P, Thakore JH. Impaired fasting glucose tolerance in first-episode, drug-naive patients with schizophrenia. Am J Psychiatry. 2003; 160:284-289.

20. de Boer C, Gaete HP. Neuroleptic malignant syndrome and diabetic keto-acidosis. Br J Psychiatry. 1992;161:856-858.

21. Kamran A, Doraiswamy PM, Jane JL, et al. Severe hyperglycemia associated with high doses of clozapine. Am J Psychiatry. 1994;151:1395.

22. Allison DB, Fontaine KR, Heo M, et al. The distribution of body mass index among individuals with and without schizophrenia. J Clin Psychiatry. 1999; 60:215-220.

23. Masand P, ed. Weight gain and antipsychotic medications. Journal of Clinical Psychiatry Visuals. Memphis: Physicians Postgraduate Press; 1999. Theme issue.

24. Layman E. Psychological effect of physical activity. In: Exercise and Sport Sciences Reviews. American College of Sports Medicine Series. New York: Academic Press; 1974:33-70.

25. Pelham TW, Campagna PD. Benefits of exercise in psychiatric rehabilitation of persons with schizophrenia. Can J Rehab. 1991;4:159-168.

26. Pelham TW, Campagna PD, Ritvo PG, et al. The effects of exercise therapy on clients in a psychiatric rehabilitation program. Psychosocial Rehab J. 1993; 16:75-84.

27. Cradock-O'Leary J, Young AS, Yano EM, et al. Use of general medical services by VA patients with psychiatric disorders. Psychiatr Serv. 2002;53:874-878.

28. Folsom DP, McCahill M, Bartels SJ, et al. Medical comorbidity and receipt of medical care by older homeless people with schizophrenia or depression. Psychiatr Serv. 2002;53:1456-1460.

29. Dickerson F, McNary S, Brown C, et al. Somatic healthcare utilization among adults with serious mental illness who are receiving community psychiatric services. Med Care. In press.

30. Redelmeier DA, Tan SH, Booth GL. The treatment of unrelated disorders in patients with chronic medical diseases. N Engl J Med. 1998;338:1516-1520.



  • Dixon L, Wohlheiter K, Thompson D. Medical management of schizophrenia. In: Lieberman J, Murray R, eds. Comprehensive Care of Schizophrenia. London: Martin Dunitz Publishers; 2000.
Related Videos
New Research Amplifies Impact of Social Determinants of Health on Cardiometabolic Measures Over Time
Where Should SGLT-2 Inhibitor Therapy Begin? Thoughts from Drs Mikhail Kosiborod and Neil Skolnik
Related Content
© 2024 MJH Life Sciences

All rights reserved.