The prevalence, risk factors, and clinical characteristics of insulin resistance in Chinese patients with schizophrenia

Insulin-resistance as a modifiable pathway to cognitive dysfunction in schizophrenia: A systematic review

BACKGROUND

Cognitive deficits are difficult to treat and negatively influence quality of life and functional outcomes of persons with schizophrenia. In the last twenty years, extensive literature demonstrated that persons with diabetes and insulin resistance (IR) also display cognitive deficits. Being type 2 diabetes (T2DM) and IR highly frequent in persons with schizophrenia, it is plausible to hypothesize that these conditions might play a role in determining dyscognition. If that is the case, acting on glucose dysmetabolism may eventually improve cognitive functioning. This review aims at: 1. evaluating the association between IR or T2DM and cognitive dysfunction in schizophrenia; 2. reviewing the evidence that pharmacological treatment of IR or T2DM may improve dyscognition in schizophrenia.

METHODS

Two systematic searches were conducted in PubMed, PsycInfo, and Scopus. We followed the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines.

RESULTS

From the first search we included 17 studies, 8 on the effects of T2DM and 9 on the effects of IR-other prediabetes measures on cognition in persons with schizophrenia. From the second search we included 12 studies investigating the effect on cognition of glucose (4 studies), insulin (2 studies), metformin (2 studies), PPAR-γ agonists (2 studies), GLP-1 agonist (1 study), bromocriptine (1 study).

CONCLUSIONS

T2DM was associated with worse cognitive function in persons with schizophrenia, while IR was less strongly associated with cognitive dysfunction. Evidence regarding the efficacy of glucose-lowering medications on cognition in schizophrenia is inconclusive, yet methodological issues likely contribute to explain conflicting results.

Fasting insulinemia as biomarker of illness relapse in patients with severe mental illness?

Severe Mental Illness (SMI) is often associated with metabolic alteration and/or metabolic syndrome, which may determine an increased mortality due to a further increased cardiovascular risk. The relationship with metabolic syndrome is often bidirectional, resulting in a pathoplastic effect of these dysmetabolisms. Among the several hormones involved, insulin appears to play a key role, albeit not entirely clear. The aim of our real-world cross-sectional observational study is to investigate a set of metabolic biomarkers of illness relapse/recurrence/onset in a cohort of 310 adult SMI inpatients consecutively admitted to the Psychiatry Clinic of the Azienda Ospedaliero Universitaria of Marche, in Ancona (Italy), between February 2021 and February 2024. According to the stepwise multivariate regression model, a higher number of acute episodes per year was positively predicted by the age of illness onset, the lifetime number of suicidal attempts and fasting insulinemia and negatively by the participant's age. A second stepwise multivariate regression model using only the metabolic characteristics as independent variables, found that a higher number of acute episodes per year was predicted positively by the fasting insulinemia and red blood cells and negatively by the abdominal circumference. Overall, our findings could provide practical implications for the treatment and management of SMI patients, emphasizing the importance of monitoring and managing metabolic factors, particularly insulinemia, metabolic syndrome and insulin resistance. Finally, insulinemia could potentially act as metabolic biomarker of illness relapse, though more larger and longitudinal studies should be carried out to confirm these results.

Clinical improvement in schizophrenia during antipsychotic treatment in relation to changes in glucose parameters: A systematic review

Antipsychotics (APs) are the cornerstone of treatment for schizophrenia (SCZ) spectrum disorders. Previous research suggests that there may be a positive association between AP-induced weight gain and/or dyslipidemia and improvement in psychiatric symptoms, often referred to as a "metabolic threshold". To determine whether a similar relationship exists for glucose parameters, we conducted a systematic search in six databases from inception to June 2022 for all longitudinal studies that directly examined the relationship between changes in glucose-related outcomes and changes in psychopathology among patients with SCZ treated with APs. We identified 10 relevant studies and one additional study that considered cognition. In most cases, we found that increased levels of fasting glucose and insulin following treatment were associated with clinical improvement. These findings contribute to existing literature that could suggest a common mechanism between AP action and metabolic side effects and support a need for additional work aimed at exploring the validity of a glucose-psychopathology relation in SCZ.

Sex Differences in the Association of HOMA-IR Index and BDNF in Han Chinese Patients With Chronic Schizophrenia

Background: Previous research has indicated that there are significant sex differences in serum BDNF levels and metabolic indicators in patients with schizophrenia. Studies have found that BDNF is involved in blood sugar regulation. Homeostasis model assessment of insulin resistance (HOMA-IR) is currently a sensitive indicator for measuring insulin resistance. Our study aims to explore the sex differences in the relationship between serum BDNF levels and HOMA-IR in patients with chronic schizophrenia (CS). Methods: A total of 332 patients with CS were enrolled in this study. General information of all participants was collected. Haematological indicators were collected, and the Positive and Negative Syndrome Scale (PANSS) was used to evaluate psychiatric symptoms. Sex differences in serum BDNF levels, HOMA-IR index and other metabolic indexes were investigated. Then, linear regression analysis was used to analyse the relationship between the HOMA-IR index and BDNF levels in male and female patients. Results: The HOMA-IR index of female patients was significantly higher than that of males, but there was no significant difference in serum BDNF levels between male patients and female patients. There was a positive correlation between BDNF level and HOMA-IR index, and this relationship only existed in female patients. Conclusion: The results show that there are significant sex differences in HOMA-IR in patients with CS. In addition, only in female patients was there a positive correlation between the HOMA-IR index and BDNF level, which suggests that sex factors should be taken into account in evaluating the relationship between BDNF and blood glucose in patients with CS.

Association Between Cardiovascular Risk Factors and Cognitive Impairment in People With Schizophrenia: A Systematic Review and Meta-analysis

IMPORTANCE

Schizophrenia is associated with cognitive dysfunction and cardiovascular risk factors, including metabolic syndrome (MetS) and its constituent criteria. Cognitive dysfunction and cardiovascular risk factors can worsen cognition in the general population and may contribute to cognitive impairment in schizophrenia.

OBJECTIVE

To study the association between cognitive dysfunction and cardiovascular risk factors and cognitive impairment in individuals with schizophrenia.

DATA SOURCES

A search was conducted of Embase, Scopus, MEDLINE, PubMed, and Cochrane databases from inception to February 25, 2020, using terms that included synonyms of schizophrenia AND metabolic adversities AND cognitive function. Conference proceedings, clinical trial registries, and reference lists of relevant publications were also searched.

STUDY SELECTION

Studies were included that (1) examined cognitive functioning in patients with schizophrenia or schizoaffective disorder; (2) investigated the association of cardiovascular disease risk factors, including MetS, diabetes, obesity, overweight, obesity or overweight, hypertension, dyslipidemia, and insulin resistance with outcomes; and (3) compared cognitive performance of patients with schizophrenia/schizoaffective disorder between those with vs without cardiovascular disease risk factors.

DATA EXTRACTION AND SYNTHESIS

Extraction of data was conducted by 2 to 3 independent reviewers per article. Data were meta-analyzed using a random-effects model.

MAIN OUTCOMES AND MEASURES

The primary outcome was global cognition, defined as a test score using clinically validated measures of overall cognitive functioning.

RESULTS

Twenty-seven studies involving 10 174 individuals with schizophrenia were included. Significantly greater global cognitive deficits were present in patients with schizophrenia who had MetS (13 studies; n = 2800; effect size [ES] = 0.31; 95% CI, 0.13-0.50; P = .001), diabetes (8 studies; n = 2976; ES = 0.32; 95% CI, 0.23-0.42; P < .001), or hypertension (5 studies; n = 1899; ES = 0.21; 95% CI, 0.11-0.31; P < .001); nonsignificantly greater deficits were present in patients with obesity (8 studies; n = 2779; P = .20), overweight (8 studies; n = 2825; P = .41), and insulin resistance (1 study; n = 193; P = .18). Worse performance in specific cognitive domains was associated with cognitive dysfunction and cardiovascular risk factors regarding 5 domains in patients with diabetes (ES range, 0.23 [95% CI, 0.12-0.33] to 0.40 [95% CI, 0.20-0.61]) and 4 domains with MetS (ES range, 0.15 [95% CI, 0.03-0.28] to 0.40 [95% CI, 0.20-0.61]) and hypertension (ES range, 0.15 [95% CI, 0.04-0.26] to 0.27 [95% CI, 0.15-0.39]).

CONCLUSIONS AND RELEVANCE

In this systematic review and meta-analysis, MetS, diabetes, and hypertension were significantly associated with global cognitive impairment in people with schizophrenia.

Causal Effects of Overall and Abdominal Obesity on Insulin Resistance and the Risk of Type 2 Diabetes Mellitus: A Two-Sample Mendelian Randomization Study

Overall and abdominal obesity were significantly associated with insulin resistance and type 2 diabetes mellitus (T2DM) risk in observational studies, though these associations cannot avoid the bias induced by confounding effects and reverse causation. This study aimed to test whether these associations are causal, and it compared the causal effects of overall and abdominal obesity on T2DM risk and glycemic traits by using a two-sample Mendelian randomization (MR) design. Based on summary-level statistics from genome-wide association studies, the instrumental variables for body mass index (BMI), waist-to-hip ratio (WHR), and WHR adjusted for BMI (WHRadjBMI) were extracted, and the horizontal pleiotropy was analyzed using MR-Egger regression and the MR-pleiotropy residual sum and outlier (PRESSO) method. Thereafter, by using the conventional MR method, the inverse-variance weighted method was applied to assess the causal effect of BMI, WHR, and WHRadjBMI on T2DM risk, Homeostatic model assessment of insulin resistance (HOMA-IR), fasting insulin, fasting glucose, and Hemoglobin A1c (HbA1c). A series of sensitivity analyses, including the multivariable MR (diastolic blood pressure, systolic blood pressure, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol as covariates), MR-Egger regression, weighted median, MR-PRESSO, and leave-one-out method, were conducted to test the robustness of the results from the conventional MR. Despite the existence of horizontal pleiotropy, consistent results were found in the conventional MR results and sensitivity analyses, except for the association between BMI and fasting glucose, and WHRadjBMI and fasting glucose. Each one standard deviation higher BMI was associated with an increased T2DM risk [odds ratio (OR): 2.741; 95% confidence interval (CI): 2.421-3.104], higher HbA1c [1.054; 1.04-1.068], fasting insulin [1.202; 1.173-1.231], and HOMA-IR [1.221; 1.187-1.255], similar to findings for causal effect of WHRadjBMI on T2DM risk [1.993; 1.704-2.33], HbA1c [1.061; 1.042-1.08], fasting insulin [1.102; 1.068-1.136], and HOMA-IR [1.127; 1.088-1.167]. Both BMI (P = 0.546) and WHRadjBMI (P = 0.443) were unassociated with fasting glucose in the multivariable MR analysis. In conclusion, overall and abdominal obesity have causal effects on T2DM risk and insulin resistance but no causal effect on fasting glucose. Individuals can substantially reduce their insulin resistance and T2DM risk through reduction of body fat mass and modification of body fat distribution.