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Critical Appraisal Of Epidemiological Study

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Schizophrenia is a serious mental disorder that interferes with the ability of a person to think, make decisions, manage emotions and relate to others. It manifests commonly in the form of hallucinations or delusions. Cognitive issues such as, disorganized thinking, struggling to remember things and lack of insight (anosognosia) are often observed. Clozapine is one of the most commonly used atypical antipsychotics to treat schizophrenia (Leutwyler et al., 2014). It leads to a decrease in suicidal ideation. However, there are some serious side effects associated with its administration. One such effect is weight gain (Gressier et al., 2016). People under this medication report significant weight gain. This drug-induced weight gain is identified as a major risk factor for disorders that can increase morbidity and mortality rates of schizophrenic patients (Sagy, Weizman & Katz, 2014). This report aims to critically appraise a study that was conducted to evaluate the effects of physical activity and diet control on obese schizophrenic patients, under clozapine treatment (Wu et al., 2007).

The paper focuses on a randomized, controlled study that was conducted to evaluate the effects of regular physical activity and continuous dietary control, for six months, on obese patients who were suffering from schizophrenia. These patients were being administered clozapine to reduce their mental disorder. The study tried to establish an association between clozapine use and weight gain among schizophrenia patients.

It assessed biochemical and anthropometric parameters such as, triglyceride, serum glucose, insulin, cholesterol, prolactin, cortisol, and growth hormones for three months and six months.

The study was a novel research as no other study had been conducted prior to this research that investigated the effects of dietary control among the target population, who were under clozapine medication (Wu et al., 2007).

The study recruited 753 hospitalized patients who had been diagnosed with DSM-IV schizophrenia (McLean et al., 2014). The age of the participants ranged between 18-65 years. Respondents who were under administration of 300mg oral clozapine per day, for at least one year and had a BMI higher than 27 kg/m2 were included in the study.

A registered dietitian implemented dietary control among the respondents and restricted the caloric intake to 1,600-1,800 kcal per day for men and 1,300-1,500 kcal per day for women. Minimum dietary requirements for men and women were 1,500 kcal and 1,200 kcal per day respectively (Dipasquale et al., 2013). The types of foods consumed by the participants were assessed, which included an evaluation of the vegetable, fruits, sugar free drinks and, artificial sweeteners (Kim et al., 2017). The calorie intake was measured.


A minimum of 30 minutes of moderate intensity physical activity like brisk walking is recommended for people belonging to all age groups for most days of the week.  The intervention involved performing physical activities for six months, three days a week. The patients were made to take part in activities that involved 1.62 km level walking for 40 minutes and walking up and down the stairs for 20 minutes, under supervision (231 steps upstairs and 330 steps downstairs). The speed and distance of these activities were maintained at a constant level, throughout the intervention period.  The participants were encouraged to complete them in an hour.

The guidelines proposed by the American College of Sports Medicine were used to estimate the rate of energy expenditure per week (Thompson et al., 2013). The effects of the interventions were assessed by anthropogenic measurements, which included measuring the body fat percentage, weight, height, hip and waist circumference and BMI (Lau et al., 2016). Serum glucose, insulin, cholesterol, cortisol, triglyceride and prolactin levels were measured by ELISA tests.

On comparing the result values of the sample and control group using ANCOVA and SPSS software version 10.0, no significant difference was observed among the two groups at baseline.  No significant changes in body fat percentages were observed between men and women or during the 3 month and 6 month intervention period. However, significant reduction (p<0.05) was observed in body weight, waist circumference in the study group, after 3 months. Waist circumference showed significant reduction after 6 months. Metabolic analysis and ELISA failed to show any reduction at baseline or during the 3 month intervention period. However, triglyceride levels were significantly lower in the control group after 6 months (p<0.05). A high IGF-1 to IGFBP-3 molar ratio was observed in the study group than the control group, after 6 months.

The study found out that physical activity and dietary are responsible for normalizing metabolic abnormalities, attenuating neuroleptic side effects and minimizing hormonal changes. However, the researchers found presence of low motivation among psychiatric patients for weight reduction, in absence of supervision (Vancampfort et al., 2015). They also proposed that it is difficult to suppress appetite for a long period of time. Therefore, they suggested that long-term adherence to such lifestyle modification programs are necessary for putting these interventions to practice.


Bias and Confounding variables

Randomised control studies are generally less susceptible to sample bias, when compared to other study designs that assess the effect of several therapeutic interventions. The study avoided bias on the basis of baseline prognostic variables. Randomisation ensured that the treatment groups were balanced and as similar as possible. This was supported by the fact that all 53 participants selected from 753 hospitalised patients had a DSM-IV schilzophrenia diagnosis, were 18-65 years of age, had BMI higher than 27 kg/m2 and was under the medication of 300 mg oral clozapine intake for more than a year. No patients were included in the study if they were found to suffer from organ failure, abnormal ambulatory functions, and severe mental retardation or presented vented walking. Neither of the sample or control group included patients who were under medication of antipsychotics apart from clozapine.

Moreover, bias due to presence of confounding variables was also removed by performing the two way mixed designs ANCOVA. This eliminated the influence of any external factors on the measured outcomes.  The results obtained were therefore least likely to get affected. However, one major bias associated with the study was the recruitment of participants from inpatient settings. The rates of compliance to the 6 month intervention and the success rate of the study would have been different if the sample was selected from outpatient settings. Thus, it can be stated that the randomized controlled study did not remove bias with respect to selection of participants from a larger population.

Chance variations are inherent errors in predictive statistical models. They are defined as the difference between actual and predicted values of the variable being investigated. Similar to other epidemiological studies, this research also included participants from a larger population. There was a chance of the small sample differing from the wider patient population (Nuzzo, 2014). To show that the difference in results between the sample and the control group reflected a real difference in the parent population, a statistical test was performed. The p

Causal association between exposure and outcome

The primary goal of most epidemiological studies is assessment of a particular disease cause. However, owing to the concept that most epidemiological studies are based on observation, rather than experiment, several possible explanations are considered before drawing inference for any cause and effect relationship. Causal relationships are more likely to demonstrate a stronger association between the cause and outcome in a particular study. Plausibiity establishes the cause-effect relationship between a biological factor and an adverse health outcome or effect. In this research study, a relationship was established between use of clozapine and weight gain among patients with schizophrenia. The study was built on the basis of several scientific researches that proposed that clozapine and olanzapine induced mean weight gain among patients who were under administration of these drugs for more than 6 months (Samara, & Leucht, 2016). The research was based on other findings that such increase in mean weight, induced by the action of antipsychotics like clozapine often leads to noncompliance (Olfson et al., 2016). This results in treatment discontinuation and relapse of psychotic symptoms. Furthermore, scientific evidences suggest that weight control is effective in reducing health risks among schizophrenia patients who are overweight.

The presence of existing biological research on the use of clozapine among such patients and their subsequent weight gain explains the association of interest of this research. Demonstrating the plausibility of causal relationships is complex since a particular health outcome is the result of balance and interplay between different factors. The study showed consistency with other findings, which indicated that schizophrenia patients who were treated with clozapine, reported a gain in weight (McNamee et al., 2013). These patients also demonstrated an increase in body fat deposits and BMI. A marked increase in the waist-to-hip ratio and central adiposity was reported by other studies. These outcomes were consistent with the findings of the current epidemiological research (Rosenbaum et al., 2014).

Moreover, the results are also consistent with other studies that indicate a loss in weight among inpatients who took clozapine. The study also showed agreement with several other findings in the low levels of IGFBP-3 and high IGF-1 to IGFBP-3 molar ratio after six months of intervention. These results were consistent with research that displayed a reduction in IGFBP-3 levels with exercise.

The special mechanism illustrated in the study focused on the effect of IGF-1 on the cardiovascular system. IGF-1 is a peptide hormone predominantly produced by the liver, in response to pituitary growth hormone. Several studies have elaborated on the role of low levels of IGF-1 in increasing the likelihood for cardiovascular diseases (Arcopinto et al., 2014). Low levels have been shown to promote atherosclerosis and stroke. This in turn increases the mortality rates.

An increase in the level of IGF-1 in macrophages works to removed the plaques from clogged arteries and prevents the incidence of cardiovascular diseases (Troncoso et al., 2014). This study therefore elaborated on the fact that IGFBP-3 (insulin-like growth factor–binding protein-3) is the most abundant protein that carries the maximum amount of IGFs that circulate in the bloodstream.  The study performed an ELISA test to investigate the molar ratio of IGF-1 to IGFBP-3, to determine the risk of cardiovascular diseases among the participants taken from inpatient settings, who were under clozapine treatment for schizophrenia. Although, previous studies did not investigate the role of IGF-1, IGFBP-3 and growth hormones among schizophrenic patients, this research illustrated the effects of long term clozapine therapy on the factors.


Appraising external validity

External validity measures the validity of the inferences obtained from the particular study to wider population. A research study is considered to be externally valid if the relevant results can be extrapolated to a larger population with similar characteristic features. The population, setting, interventions and treatment outcomes of this study can be applied to the source population of schizophrenia patients who adhered to clozapine medication. The interventions followed in this study could therefore be followed in the source population. The effects of dietary control and physical exercise could be applied to monitor the health effects of obese inpatients with schizophrenia, who were subjected to clozapine drugs (Mizuno et al., 2014).

However, the external validity cannot be completely established before the interventions are applied to outpatient settings. Participants belonging to outpatient settings have a less likelihood of showing adherence to the interventions and following a strict dietary and exercise regime. The results of the intervention on such participants are therefore most likely to get altered. Such patients would show less success rate of the proposed intervention. Furthermore, other metabolic effects of the interventions were not diagnosed before the 6 month period. Therefore, before being applied to a larger population, the study parameters should be tested on outpatients and the secondary metabolic effects of the lifestyle modifications should be measured.  

Quality of the study

The discussions prove that the study was successful in measuring the effects of physical activity and dietary control on the 53 participants, randomly distributed in the sample and control group. It effectively demonstrated the benefits of a 3 month and 6 month intervention that consisted of regular physical activity and integrated dietary control on obese patients, who suffered from schizophrenia and were subjected to clozapine treatment. The interventions were successful in showing significant reduction in body fat percentage, BMI and waist and hip circumference (Amiaz et al., 2016). In addition, the study effectively measured the insulin, triglyceride, cortisol, serum glucose, prolactin, IGF-1 and IGF-3 levels and their molar ratio among the participating patients. The results showed significant improvement in their metabolic profiles. In contrast, negligible or no improvement in the control group results for anthropometric measurements established the fact that the interventions were effective in managing weight gain in the sample.


It can also be suggested that the study was of a good quality owing to the fact that the dietary control intervention was applied on the participants by following dietary guidelines.  Approximately 200-300 fewer kilocalories were present in the diet of the participants during the 6 month intervention period and they were made to spend 600-750 kcal more energy per week by regular physical activity. The study chose these levels for calorie consumption or energy expenditure to minimize occurrence of adverse effects due to diet changes. These adverse events could be manifested in the form of emotional and mental instability among inpatients that were given fewer calories. Moreover, the study was of a good quality in selecting physical activities that were suitable for the patients. The activities chosen were uncomplicated and did not pose any danger. Furthermore, it utilized the role of efficient health professionals to evaluate and ensure the proper application of the weight management techniques among the patients. A minimum body weight reduction by 5% to 10% produces significant health benefits among the patients (Manu et al., 2015). The results showed that there was a significant reduction in for obese patients with schizophrenia who are taking clozapine, the intervention resulted in body weight (5.4%), BMI (5.4%), hip circumference (3.3 cm) and waist circumference (3.3 cm) after the 6 month intervention period.

The research was effective in lowering BMI and improving other outcome measures by the end of the intervention period. A reduction was observed in some of the parameters just after 3 months of intervention, while others showed significant changes in results after 6 months. These discussion state that the research considered appropriate intervention strategies to evaluate the intended outcomes. Moreover, the study focused on regular monitoring the anthropometric measurements, dietary behavior and physical activity of the sample group, by the ward staff and the investigators. At the end of the 6 month period, none of the participants displayed worsened conditions. Female patients with schizophrenia under clozapine medications are likely to get affected with cardiovascular diseases. The findings provided evidence for low IGFB-3 levels after the 6 month intervention but, failed to show any alteration of the levels of IGF-1. Therefore, it can be stated that the exercise intensity used in the intervention was inadequate to create changes in the levels of the growth hormone.


Thus, it can be concluded that the study helped to establish the benefits of regular physical activity and dietary control among the target population. The intervention showed significant improvements among obese, schizophrenia inpatients that were treated with clozapine.  However, a strong health monitoring and lifestyle modifications are required to observe the long term effect of the interventions.



Amiaz, R., Rubinstein, K., Czerniak, E., Karni, Y., & Weiser, M. (2016). A diet and fitness program similarly affects weight reduction in schizophrenia patients treated with typical or atypical medications. Pharmacopsychiatry, 26(03), 112-116.

Arcopinto, M., Isgaard, J., Marra, A. M., Formisano, P., Bossone, E., Vriz, O., ... & Cittadini, A. (2014). IGF-1 predicts survival in chronic heart failure. Insights from the TOS CA.(Trattamento Ormonale Nello Scompenso CArdiaco) registry. International journal of cardiology, 176(3), 1006-1008.

Dipasquale, S., Pariante, C. M., Dazzan, P., Aguglia, E., McGuire, P., & Mondelli, V. (2013). The dietary pattern of patients with schizophrenia: a systematic review. Journal of psychiatric research, 47(2), 197-207.

Gressier, F., Porcelli, S., Calati, R., & Serretti, A. (2016). Pharmacogenetics of clozapine response and induced weight gain: a comprehensive review and meta-analysis. European Neuropsychopharmacology, 26(2), 163-185.

Kim, E. J., Lim, S. Y., Lee, H. J., Lee, J. Y., Choi, S., Kim, S. Y., ... & Kim, S. W. (2017). Low dietary intake of n-3 fatty acids, niacin, folate, and vitamin C in Korean patients with schizophrenia and the development of dietary guidelines for schizophrenia. Nutrition Research, 45, 10-18.

Lau, S. L., Muir, C., Assur, Y., Beach, R., Tran, B., Bartrop, R., ... & Caetano, D. (2016). Predicting weight gain in patients treated with clozapine: the role of sex, body mass index, and smoking. Journal of clinical psychopharmacology, 36(2), 120-124.

Leutwyler, H., Hubbard, E. M., Jeste, D. V., Miller, B., & Vinogradov, S. (2014). Associations of schizophrenia symptoms and neurocognition with physical activity in older adults with schizophrenia. Biological research for nursing, 16(1), 23-30.

Manu, P., Dima, L., Shulman, M., Vancampfort, D., De Hert, M., & Correll, C. U. (2015). Weight gain and obesity in schizophrenia: epidemiology, pathobiology, and management. Acta Psychiatrica Scandinavica, 132(2), 97-108.

McLean, D., Thara, R., John, S., Barrett, R., Loa, P., McGrath, J., & Mowry, B. (2014). DSM-IV “criterion A” schizophrenia symptoms across ethnically different populations: evidence for differing psychotic symptom content or structural organization?. Culture, Medicine, and Psychiatry, 38(3), 408-426.

McNamee, L., Mead, G., MacGillivray, S., & Lawrie, S. M. (2013). Schizophrenia, poor physical health and physical activity: evidence-based interventions are required to reduce major health inequalities.

Mizuno, Y., Suzuki, T., Nakagawa, A., Yoshida, K., Mimura, M., Fleischhacker, W. W., & Uchida, H. (2014). Pharmacological strategies to counteract antipsychotic-induced weight gain and metabolic adverse effects in schizophrenia: a systematic review and meta-analysis. Schizophrenia bulletin, 40(6), 1385-1403.

Nuzzo, R. (2014). Statistical errors. Nature, 506(7487), 150.

Olfson, M., Gerhard, T., Crystal, S., & Stroup, T. S. (2016). Clozapine for schizophrenia: state variation in evidence-based practice. Psychiatric Services, 67(2), 152-152.

Rosenbaum, S., Tiedemann, A., Sherrington, C., Curtis, J., & Ward, P. B. (2014). Physical activity interventions for people with mental illness: a systematic review and meta-analysis.

Sagy, R., Weizman, A., & Katz, N. (2014). Pharmacological and behavioral management of some often-overlooked clozapine-induced side effects. International clinical psychopharmacology, 29(6), 313-317.

Samara, M. T., & Leucht, S. (2016). Use of Clozapine in Schizophrenia—Reply. JAMA psychiatry, 73(10), 1098-1099.

Thompson, P. D., Arena, R., Riebe, D., & Pescatello, L. S. (2013). ACSM’s new preparticipation health screening recommendations from ACSM’s guidelines for exercise testing and prescription. Current sports medicine reports, 12(4), 215-217.

Troncoso, R., Ibarra, C., Vicencio, J. M., Jaimovich, E., & Lavandero, S. (2014). New insights into IGF-1 signaling in the heart. Trends in Endocrinology & Metabolism, 25(3), 128-137.

Vancampfort, D., De Hert, M., Stubbs, B., Ward, P. B., Rosenbaum, S., Soundy, A., & Probst, M. (2015). Negative symptoms are associated with lower autonomous motivation towards physical activity in people with schizophrenia. Comprehensive psychiatry, 56, 128-132.

Wu, M. K., Wang, C. K., Bai, Y. M., Huang, C. Y., & Lee, S. D. (2007). Outcomes of obese, clozapine-treated inpatients with schizophrenia placed on a six-month diet and physical activity program. Psychiatric services, 58(4), 544-550.


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