In the past few years, numerous publications have suggested that serious mental illnesses are associated with an increased prevalence of type 2 diabetes. In 2004, Dixon et al. published a study titled “A Comparison of Type 2 Diabetes Outcomes among Persons With and Without Severe Mental Illnesses” that compared the glycosylated hemoglobin (HbA1c) levels of patients who had type 2 diabtes and schizophrenia with those patients who had type 2 diabetes and major mood disorders and those who had type 2 diabtes but who did not have severe mental illness.
The authors hypothesized that “persons with schizophrenia would have worse (higher) HbA1c values than the other two groups “(Dixon 893). This critique is intended to review the article written by Dixon et al. and to assess both its strengths and weaknesses based on the objectives stated. The objective of the study by Dixon et al. was to compare the HbA1c levels in diabetic patients with severe mental illnesses to those without severe mental illness. The study was done by recruiting a sample of 300 patients with type 2 diabetes: 100 w/ schizophrenia, 101 w/ major mood disorders, and 99 had no identified severe mental illness.
The proposed hypothesis was not supported by the data collected in this study. Results found that although all three groups had mean HbA1c values that exceeded the recommended levels, the patients who had schizophrenia had significantly lower HbA1c levels than among patients who did not have severe mental illness. Results were not significantly different from those patients who had major depressive disorders. One of the strengths of this article is the abundance of information provided and its organization.
The introduction provides a history of the topic, education on HbA1c levels, and previous research results done using primary evidence. Most importantly, the objectives, purpose, and hypothesis are all clearly stated. This study focused on outcomes rather than the usual studies that focus on incidence and prevalance of disease. Another strength of the study is that it looked at many different characteristics of all three groups including demographics, self-care variables, number of hospitalizations, BMI, adherence to medications, and many more.
The study used multiple statistical tests and frequency-matched the different variables between groups. When the results rejected the hypothesis, the authors gave numerous possible explanations and recommendations for future studies. The major problem with this cross-sectional study is that it only reports data on the 300 patients at that exact moment in time. The study design tells us how long the patient has had diabetes, but not how long they have had a mental illness.
So the question is how do we know what came first: schizophrenia, an antipsychotic treatment, or diabetes? This design is good to assess the burden of diabetes on each group, but it gives no causal pathway to examine. In agreement with the authors future recommendations, further research should consider following cohorts of patients over an extended period of time. Another weakness noted is the sample of patients with schizophrenia were recruited from mental health centers and patients without mental illness were recruited from primary care centers.
The patients with schizophrenia may be receiving mental health services regularly which contributes to stability and adherence to diabetes treatment. Another weakness is the wide range of ages (18 to 65 years old) which may play a role in severity of the illness and adherence to treatment regimens. The patients with schizophrenia were younger than the patients in the other two groups partly because all of the patients with schizophrenia who declined to participate were of older age (avg. = 62. 7 y. o).
Further research should also include data about concurrent medications being used. This study only looked at olanzapine and failed to assess the patients use of any other anti-psychotic drugs, anti-hypertensives, etc. Furthermore, the study did not assess the length of time over which medications were prescribed, and the overall level of adherence. Due to the many risk factors associated with diabetes, it is hard to pin-point one specific aspect of schizophrenia that is contributing to the high prevalance of diabetes.
The results of this study are not consistent with other research and more detailed, extensive studies need to be done in the future. Although the published article was well-written and very educational, it wasn’t enough to support the hypothesis. Primary care givers need to be aware of the diabetes risk among those with severe mental illness and provide the education necessary to promote adherence to the treatment plan. References Dixon, Lisa B et al. A Comparison of Type 2 Diabetes Outcomes among Persons With and Without Severe Mental Illnesses. 2004. Pyschiatric Services. 55; 892-900.