Investigating the pro-cognitive and anti-depressant efficacy of metformin: A systematic review and meta-analysis of randomised controlled trials

Age of onset, sociodemographic, and clinical predictors of depression: a population-based study in Rural Southern Iran

BACKGROUND

Depression is the leading cause of disability worldwide and a growing public health concern. In Iran, the prevalence of depression has shown an increasing trend, with rural populations facing unique challenges in access to mental health care. This study aimed to determine sociodemographic and clinical predictors of depression and explore how these factors influence age at onset in a rural population, providing valuable insights for preventive strategies.

METHODS

The present cross-sectional investigation utilized baseline data of the Fasa PERSIAN Cohort, comprising 10,133 adults aged 35 and older from a rural region in southern Iran. Depression diagnoses were based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria. Logistic regression analyses were conducted to identify predictors of depression, while linear regression models examined associations between baseline characteristics and age at depression onset.

RESULTS

Among participants, 6.7% met the criteria for depression, with a higher prevalence among females (78.7%) and the unemployed (70.9%). Independent predictors included female sex, unemployed status, literacy, diabetes, fatty liver disease, and psychiatric comorbidities, which emerged as the strongest predictor (odds ratio = 6.605, p < 0.001). The average age at depression onset was 39.5 years, with men experiencing onset earlier than women. Earlier onset was also associated with higher education levels, opioid use, psychiatric comorbidities, and higher energy intake, whereas later onset was linked to medical conditions, including hypertension, cardiovascular disease, and stroke.

CONCLUSION

This study highlights important demographic and clinical factors linked to depression and its age of onset, underscoring the complex interplay between sociodemographic characteristics, lifestyle factors, and comorbidities. These findings can guide targeted mental health interventions and support tailored prevention strategies in similar rural populations.

Metformin and Cognitive Performance in Patients With Type 2 Diabetes: An Umbrella Review

Contradictory results for the association between metformin intake and changes in cognitive function have been reported. We attempted to overview systematic reviews and meta-analyses showing the role of metformin, as mono or combination therapy, in cognitive performance alterations among patients with type 2 diabetes mellitus (T2DM) and to determine the quality of the evidence as well. To find the English-written reviews, a literature search was conducted on PubMed, Web of Science, Scopus, Cochrane Library, Trip, and Google Scholar by May 1, 2023. The literature search unearthed 2672 records, 10 of which were included in the study. Metformin may provide cognitive benefits for patients with type 2 diabetes, as evidence suggests potential improvements in memory and a reduced risk of neurodegenerative diseases. Even though the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) score alterations correspond to raising concerns about cognitive decline, Mini-Mental State Examination (MMSE) and selective reminding test (SRT) score improvements support metformin's role in improving specific cognitive domains. As such, metformin may exert differential impacts on various aspects of cognitive performance in these patients. However, the inconsistency and low quality of current evidence point toward the need for accurate research to elucidate whether metformin's cognitive effects are protective, neutral, or context-dependent based on patient profiles.

High Rates of Abnormal Glucose Metabolism Detected by 75 g Oral Glucose Tolerance Test in Major Psychiatric Patients with Normal HbA1c and Fasting Glucose Levels

Objectives: Comorbid diabetes is an important factor in the treatment of major psychiatric disorders. However, a substantial proportion of diabetic patients remain undetected by routine diabetic indices such as blood glucose and HbA1c. This study tried to estimate rates of such unidentified diabetic or prediabetic patients by using a 75 g oral glucose tolerance test (OGTT). Methods: Participants in the test were 25 patients with major depressive disorder (MDD), 28 patients with bipolar disorder (BP), 26 patients with schizophrenia, and 28 psychiatrically normal controls. They were all Japanese, and showed non-diabetic levels of blood glucose (<126 mg/dL) and HbA1c (<6.0%). Results: Relatively high rates of psychiatric patients showed diabetes mellites (DM)-type abnormality (32% of MDD, 21.4% of BP and 42.3% of schizophrenia v. 10.7% of controls). The difference in the rates between schizophrenia and control groups was statistically significant (p = 0.008). When abnormal glucose metabolism was defined as a prediabetic state (either normal high glycemia, impaired fast glycemia or impaired glucose tolerance) or DM type in OGTT, it was more frequently seen in the psychiatric patients than in controls (64% of MDD, 46.4% of BP and 46.2% of schizophrenia v. 35.7% of controls). Individuals with DM type showed higher HbA1c values compared with those with normal (p < 0.001) and prediabetic (p = 0.021) states. Conclusions: The results suggest that relatively high proportions of patients with a major psychiatric disorder remain undetected by routine indices for abnormal glucose metabolism, indicating the importance of OGTT even if the patients showed non-diabetic levels in blood glucose or HbA1c.

The interface of depression and diabetes: treatment considerations

This state-of-the-art review explores the relationship between depression and diabetes, highlighting the two-way influences that make treatment challenging and worsen the outcomes of both conditions. Depression and diabetes often co-occur and share genetic, lifestyle, and psychosocial risk factors. Lifestyle elements such as diet, physical activity, and sleep patterns play a role on the development and management of both conditions, highlighting the need for integrated treatment strategies. The evidence suggests that traditional management strategies focusing on either condition in isolation fall short of addressing the intertwined nature of diabetes and depression. Instead, integrated care models encompassing psychological support and medical management are recommended to improve treatment efficacy and patient adherence. Such models require collaboration across multiple healthcare disciplines, including endocrinology, psychiatry, and primary care, to offer a holistic approach to patient care. This review also identifies significant patient-related barriers to effective management, such as stigma, psychological resistance, and health literacy, which need to be addressed through patient-centered education and support systems. Future directions for research include longitudinal studies in diverse populations to further elucidate causal relationships and the exploration of novel therapeutic targets, as well as the effectiveness of healthcare models aimed at preventing the onset of one condition in individuals diagnosed with the other.

Metformin reprograms tryptophan metabolism via gut microbiome-derived bile acid metabolites to ameliorate depression-Like behaviors in mice

As an adjunct therapy, metformin enhances the efficacy of conventional antidepressant medications. However, its mode of action remains unclear. Here, metformin was found to ameliorate depression-like behaviors in mice exposed to chronic restraint stress (CRS) by normalizing the dysbiotic gut microbiome. Fecal transplants from metformin-treated mice ameliorated depressive behaviors in stressed mice. Microbiome profiling revealed that Akkermansia muciniphila (A. muciniphila), in particular, was markedly increased in the gut by metformin and that oral administration of this species alone was sufficient to reverse CRS-induced depressive behaviors and normalize aberrant stress-induced 5-hydroxytryptamine (5-HT) metabolism in the brain and gut. Untargeted metabolomic profiling further identified the bile acid metabolites taurocholate and deoxycholic acid as direct A. muciniphila-derived molecules that are, individually, sufficient to rescue the CRS-induced impaired 5-HT metabolism and depression-like behaviors. Thus, we report metformin reprograms 5-HT metabolism via microbiome-brain interactions to mitigate depressive syndromes, providing novel insights into gut microbiota-derived bile acids as potential therapeutic candidates for depressive mood disorders from bench to bedside.

Efficacy and Safety of Antidiabetic Agents for Major Depressive Disorder and Bipolar Depression: A Meta-Analysis of Randomized, Double-Blind, Placebo-Controlled Trials

BACKGROUND

This meta-analysis aimed to determine the efficacy and safety of antidiabetic agents in the treatment of major depressive disorder and bipolar depression.

METHODS

Randomized controlled trials (RCTs) of antidiabetic agents in major depressive disorder or bipolar depression were searched in three electronic databases and three clinical trial registry websites from their inception up to October 2023. The differences in changes in the depression rating scale scores from baseline to endpoint or pre-defined sessions, response rate, remission rate, rate of side effects and dropout rate between antidiabetic agents and placebo were meta-analyzed.

RESULTS

Six RCTs involving 399 participants were included in the final meta-analysis, which did not find that antidiabetics outperformed the placebo in reducing depressive symptoms. The standardized mean difference (SMD) in the depression scores from baseline to endpoint was 0.25 (95% CI -0.1, 0.61). However, a subgroup analysis found a significant difference between antidiabetics and placebos in reducing depressive symptoms in Middle Eastern populations, with an SMD of 0.89 (95% CI 0.44, 1.34).

CONCLUSIONS

The current meta-analysis does not support the efficacy of antidiabetics being superior to the placebo in the treatment of unipolar and bipolar depression. However, a subgroup analysis indicates that patients from the Middle East may benefit from adding an antidiabetic medication to their ongoing medication(s) for their depression. Larger studies with good-quality study designs are warranted.

Diabetes, antidiabetic medications and risk of dementia: A systematic umbrella review and meta-analysis

AIMS

The objective of this umbrella review and meta-analysis was to evaluate the effect of diabetes on risk of dementia, as well as the mitigating effect of antidiabetic treatments.

MATERIALS AND METHODS

We conducted a systematic umbrella review on diabetes and its treatment, and a meta-analysis focusing on treatment. We searched MEDLINE/PubMed, Embase, PsycINFO, CINAHL and the Cochrane Library for systematic reviews and meta-analyses assessing the risk of cognitive decline/dementia in individuals with diabetes until 2 July 2023. We conducted random-effects meta-analyses to obtain risk ratios and 95% confidence intervals estimating the association of metformin, thiazolidinediones, pioglitazone, dipeptidyl peptidase-4 inhibitors, α-glucosidase inhibitors, meglitinides, insulin, sulphonylureas, glucagon-like peptide-1 receptor agonists (GLP1RAs) and sodium-glucose cotransporter-2 inhibitors (SGLT2is) with risk of dementia from cohort/case-control studies. The subgroups analysed included country and world region. Risk of bias was assessed with the AMSTAR tool and Newcastle-Ottawa Scale.

RESULTS

We included 100 reviews and 27 cohort/case-control studies (N = 3 046 661). Metformin, thiazolidinediones, pioglitazone, GLP1RAs and SGLT2is were associated with significant reduction in risk of dementia. When studies examining metformin were divided by country, the only significant effect was for the United States. Moreover, the effect of metformin was significant in Western but not Eastern populations. No significant effect was observed for dipeptidyl peptidase-4 inhibitors, α-glucosidase inhibitors, or insulin, while meglitinides and sulphonylureas were associated with increased risk.

CONCLUSIONS

Metformin, thiazolidinediones, pioglitazone, GLP1RAs and SGLT2is were associated with reduced risk of dementia. More longitudinal studies aimed at determining their relative benefit in different populations should be conducted.

The Antidepressant Effects of GLP-1 Receptor Agonists: A Systematic Review and Meta-Analysis

AIM/HYPOTHESIS

Emerging evidence suggests that glucagon-like peptide-1 receptor agonists (GLP-1RAs) may exert positive effects in patients with depression. Our aim was to conduct a systematic review and meta-analysis to examine the antidepressant effects of GLP-1RAs.

METHODS

Randomized controlled trials and prospective cohort studies investigating the effects of GLP-1RAs versus placebo or other antidiabetic therapies on depressive symptoms were searched for using multiple electronic sources (CENTRAL, PubMed, EMBASE, PsycINFO, World Health Organization International Clinical Trials Registry Platform, ClinicalTrials.gov, China Network Knowledge Infrastructure, China Biomedical Database, Wan Fang data, and Chinese Scientific Journals Database) from inception to February 16, 2023. We utilized a random effects model to analyze standardized mean differences for the change in depression rating scales comparing GLP-1RA treated groups with control treated groups.

RESULTS

The meta-analysis comprising 2,071 participants included 5 randomized controlled trials and 1 prospective cohort study. The meta-analysis indicated that the change from baseline in depression rating scale scores decreased significantly when patients received treatment with GLP-1RAs compared to control treatments (SMD = -0.12, 95% CI [-0.21, -0.03], pSMD <0.01, I2 = 0%, pQ = 0.52). The subgroup analysis showed that the effects of GLP-1RAs on depressive symptoms were consistent in patients with Type 2 diabetes mellitus (SMD = -0.12, 95% CI [-0.21, -0.03], pSMD <0.01, I2 = 2%, pQ = 0.40).

CONCLUSIONS

Adults treated with GLP-1RAs showed significant reductions in the depression rating scale scores compared to those treated with control substances. Our findings suggest that GLP-1RAs may be a potential treatment for alleviating depressive symptoms in humans.

Resilience and Vulnerability to Stress-Induced Anhedonia: Unveiling Brain Gene Expression and Mitochondrial Dynamics in a Mouse Chronic Stress Depression Model

The role of altered brain mitochondrial regulation in psychiatric pathologies, including Major Depressive Disorder (MDD), has attracted increasing attention. Aberrant mitochondrial functions were suggested to underlie distinct inter-individual vulnerability to stress-related MDD syndrome. In this context, insulin receptor sensitizers (IRSs) that regulate brain metabolism have become a focus of recent research, as their use in pre-clinical studies can help to elucidate the role of mitochondrial dynamics in this disorder and contribute to the development of new antidepressant treatment. Here, following 2-week chronic mild stress (CMS) using predation, social defeat, and restraint, MDD-related behaviour and brain molecular markers have been investigated along with the hippocampus-dependent performance and emotionality in mice that received the IRS dicholine succinate (DS). In a sucrose test, mice were studied for the key feature of MDD, a decreased sensitivity to reward, called anhedonia. Based on this test, animals were assigned to anhedonic and resilient-to-stress-induced-anhedonia groups, using a previously established criterion of a decrease in sucrose preference below 65%. Such assignment was based on the fact that none of control, non-stressed animals displayed sucrose preference that would be smaller than this value. DS-treated stressed mice displayed ameliorated behaviours in a battery of assays: sucrose preference, coat state, the Y-maze, the marble test, tail suspension, and nest building. CMS-vulnerable mice exhibited overexpression of the inflammatory markers Il-1β, tnf, and Cox-1, as well as 5-htt and 5-ht2a-R, in various brain regions. The alterations in hippocampal gene expression were the closest to clinical findings and were studied further. DS-treated, stressed mice showed normalised hippocampal expression of the plasticity markers Camk4, Camk2, Pka, Adcy1, Creb-ar, Nmda-2r-ar, and Nmda-2r-s. DS-treated and non-treated stressed mice who were resilient or vulnerable to anhedonia were compared for hippocampal mitochondrial pathway regulation using Illumina profiling. Resilient mice revealed overexpression of the mitochondrial complexes NADH dehydrogenase, succinate dehydrogenase, cytochrome bc1, cytochrome c oxidase, F-type and V-type ATPases, and inorganic pyrophosphatase, which were decreased in anhedonic mice. DS partially normalised the expression of both ATPases. We conclude that hippocampal reduction in ATP synthesis is associated with anhedonia and pro-inflammatory brain changes that are ameliorated by DS.

Clinical insights into the cross-link between mood disorders and type 2 diabetes: A review of longitudinal studies and Mendelian randomisation analyses

Mood disorders and type 2 diabetes mellitus (T2DM) are prevalent conditions that often co-occur. We reviewed the available evidence from longitudinal and Mendelian randomisation (MR) studies on the relationship between major depressive disorder (MDD), bipolar disorder and T2DM. The clinical implications of this comorbidity on the course of either condition and the impact of antidepressants, mood stabilisers, and antidiabetic drugs were examined. Consistent evidence indicates a bidirectional association between mood disorders and T2DM. T2DM leads to more severe depression, whereas depression is associated with more complications and higher mortality in T2DM. MR studies demonstrated a causal effect of MDD on T2DM in Europeans, while a suggestive causal association in the opposite direction was found in East Asians. Antidepressants, but not lithium, were associated with a higher T2DM risk in the long-term, but confounders cannot be excluded. Some oral antidiabetics, such as pioglitazone and liraglutide, may be effective on depressive and cognitive symptoms. Studies in multi-ethnic populations, with a more careful assessment of confounders and appropriate power, would be important.

Depression and lifestyle: Focusing on nutrition, exercise, and their possible relevance to molecular mechanisms

Accumulating evidence has suggested the important role of lifestyle factors in depressive disorder. This paper aimed to introduce and outline recent research on epidemiological and intervention studies on lifestyle-related factors in depressive disorder with a special focus on diet. Evidence on exercise, sleep. and related behaviors is also described. Here, findings from meta-analytic studies are emphasized and related studies by the author's research group are introduced. Dietary factors that increase the risk of the illness include energy overload, skipping breakfast, unhealthy diet styles such as Western diet, inflammation-prone diet, and high consumption of ultraprocessed food (UPF). Nutritional imbalances such as inadequate intake of protein, fish (Ω3 polyunsaturated fatty acids), vitamins (folate and vitamin D), and minerals (iron and zinc) increases the risk of depression. Poor oral hygiene, food allergy, addiction to alcohol, and smoking constitute risk factors. Sedentary lifestyle and increased screen time (e.g. video games and the internet) confer the risk of depression. Insomnia and disturbed sleep-wake rhythm are also involved in the pathogenesis of depression. There is accumulating evidence at the meta-analysis level for interventions to modify these lifestyle habits in the protection and treatment of depressive disorder. Main biological mechanisms of the link between lifestyle factors and depression include monoamine imbalance, inflammation, altered stress response, oxidative stress, and dysfunction of brain-derived neurotrophic factor, although other players such as insulin, leptin, and orexin also play a role. To increase resilience to modern stress and ameliorate depression through modification of lifestyle habits, a list of 30 recommendable interventions is presented.

Assessment of cognitive impairment and depressive signs in patients with type 2 diabetes treated with metformin from Southeast Mexico: A cross-sectional study

Multiple factors associate diabetes with cognitive impairment and depression. Antidiabetic drugs have reported antidepressant and pro-cognitive effects in diabetic and non-diabetic subjects. Antidepressant and pro-cognitive effects of metformin are reported in various studies; however, these effects are not consistent among researches. We designed a cross-sectional study. We recruited patients with T2D diagnosis from the Diabetes Clinic of the Regional Hospital of High Specialty "Dr. Gustavo A. Rovirosa Pérez" from January 2019 to May 2022. We included 431 subjects with T2D, 374 patients with metformin treatment and 57 subjects without metformin. These patients were on intensive therapies and had not a previous diagnosis of cognitive impairment or depression. We applied Mini-Mental State Examination (MMSE) to evaluate cognitive impairment, and Hamilton Depression Rating Scale (HAM-D) to assess depressive signs. Our sample had a mean age of 53.77 ± 13.43 years. Metformin users were 374 individuals, and 57 subjects didn't use metformin. MMSE found cognitive impairment in 8.3% (n = 31) of metformin users, and 14.8% (n = 8) of patients without metformin. HAM-D scale showed that 39.5% (n = 147) of patients with metformin had depression signs, subjects without metformin and depressive signs were 44.6% (n = 25). We found no differences between groups for cognitive impairment and depression grades. We did not find associations between metformin treatment, cognitive impairment measures and depression sign measures. However, chronic metformin treatment, insulin use, glycemic control and age could influence our results.

The role of metformin as a treatment for neuropsychiatric illness

Advances in psychopharmacology have been significantly slower to evolve than in other disciplines of medicine and therefore investigation into novel therapeutic approaches is required. Additionally, concurrent metabolic conditions are prevalent among people with mental disorders. Metformin is a widely used hypoglycaemic agent that is now being studied for use beyond diabetes management. Evidence is emerging that metformin has multiple effects on diverse neurobiological pathways and consequently may be repurposed for treating mental illness. Metformin may have beneficial neuroimmunological, neuroplastic, neuro-oxidative and neuro-nitrosative effects across a range of psychiatric and neurodegenerative illnesses. Mechanisms include glucose lowering effects and effects on AMP-activated protein kinase (AMPK) signalling, however the best evidence for clinical benefit is through the glucose lowering effects, with other mechanisms less supported by the current evidence base. This narrative review aims to draw together the existing evidence for use of metformin as a psychopharmaceutical and present the role of metformin in the context of physical and psychiatric ill health, including metabolic, endocrinological and cancer domains. It not only has therapeutic potential in medical comorbidity but may have potential in core illness domains.