The Association Between Overall, Healthy, and Unhealthy Plant-Based Diet Index and Risk of Prediabetes and Type 2 Diabetes Mellitus: A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies

CONTEXT

The global incidence of prediabetes and type 2 diabetes mellitus (T2DM) has increased substantially in recent years. Among the established, modifiable lifestyle factors associated with favorable prediabetes and T2DM risk, healthy dietary patterns have attracted considerable attention.

OBJECTIVE

The association between adherence to plant-based dietary pattern indices (PDIs), including the overall PDI (O-PDI), healthy PDI (H-PDI), and unhealthy PDI (U-PDI), and the risk of prediabetes and T2DM was investigated in this study.

DATA SOURCES

A literature search was conducted of the PubMed/Medline, Scopus, and Web of Sciences databases from their inception to February 2024. A systematic review and meta-analysis were conducted using random effects models and dose-response analyses. The Cochran Q test and the I2 statistic were used to evaluate heterogeneity between studies.

DATA EXTRACTION

A total of 16 publications, with data on a total of 721 012 participants, were identified for the meta-analysis.

DATA ANALYSIS

According to a pooled analysis, compared with the lowest category of O-PDI and H-PDI adherence, the highest category was associated with a 14% and 19% reduction in T2DM risk, respectively, for O-PDI (effect size [ES] = 0.86; 95%CI, 0.82-0.90; I2 = 57.7) and H-PDI (ES = 0.81; 95%CI, 0.75-0.88; I2 = 82.6). Greater adherence to U-PDI was significantly associated with an 10% increase in the risk of T2DM (ES = 1.10; 95%CI, 1.04-1.16). Consistent associations were found within the predetermined subgroups. As well, there was a nonlinear inverse association between O-PDI, H-PDI, and T2DM risk. No significant association was found between adherence to O-PDI (ES = 0.87; 95%CI, 0.75-1.01; I2 = 68%), H-PDI (ES = 0.99; 95%CI, 0.87-1.13; I2 = 0.0%), and U-PDI (ES = 1.09; 95%CI, 0.94-1.21; I2 = 22.9%) and risk of prediabetes.

CONCLUSION

These findings underscore the importance of dietary selections within the framework of a plant-based dietary pattern, particularly when incorporating healthful, plant-based foods, which may have potential benefits in reducing the T2DM risk.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42023459851.

The association between plant-based diet indices and metabolic syndrome: a systematic review and dose-response meta-analysis

Aim/introduction

The prevalence of metabolic syndrome (MetS) and its components have markedly increased worldwide. Among lifestyle factors introduced to lower the risk of MetS, healthy dietary patterns have gained considerable attention. This study aimed to assess the association between adherence to plant-based diet indices including O-PDI (overall plant-based diet index), H-PDI (healthy plant-based diet index), U-PDI (unhealthy plant-based diet index), and risk of MetS development.

Methods

To find related observational studies which assessed the association between Plant-based Diet indices and risk of MetS development, PubMed/Medline, Scopus, and Web of Science databases were searched from January 2016 to November 2023. A random effects model was used to estimate pooled odds ratios (OR) and 95% confidence intervals (95% CI). To assess the heterogeneity of included studies, the I2 index was used.

Results

Nine studies including 34,953 participants from the initial 288 studies were recognized to include in this meta-analysis study. According to pooled analysis, there was a significant relationship between the adherence to H-PDI and the lower risk of MetS (ES: 0.81; 95% CI: 0.67, 0.97; I2 = 77.2%, p < 0.001), while greater adherence to U-PDI was associated with 27% increases in the risk of MetS (ES: 1.27; 95% CI: 1.05, 1.54; I2 = 76.8%, p < 0.001). According to our analysis of the association between adherence to PDIs and the risk of MetS components, greater adherence to O-PDI and H-PDI was significantly associated with a higher risk of elevated FBS and obesity, respectively. As well, greater adherence to U-PDI was significantly associated with a higher risk of obesity, hypertriglyceridemia, low HDL-C, and elevated FBS.

Conclusion

Our results highlighted the importance of food choices in the context of a plant-based dietary pattern, indicating that adherence to unhealthy plant-based dietary patterns rich in less healthful carbohydrates may induce the risk of MetS development.

Systematic review registration

PROSPERO CRD42023428981.

Maternal uric acid levels and risk of gestational diabetes mellitus: A systematic review and dose-response meta-analysis of cohort studies including 105,380 participants

AIMS/INTRODUCTION

Although the association between uric acid levels and adverse pregnancy outcomes has been investigated, the effects of higher uric acid levels on the risk of gestational diabetes mellitus (GDM) have yet to be established. Therefore, this systematic review and meta-analysis aimed to investigate the relationship between uric acid levels during pregnancy and the risk of GDM.

MATERIALS AND METHODS

PubMed/Medline, Scopus and Web of Science databases were searched up to April 2022 for relevant observational studies. A random effects model was used to estimate pooled odds ratios (OR) and 95% confidence intervals (95% CI). To assess the heterogeneity of included studies, the I2 index was used.

RESULTS

Among the initial 262 studies that were recognized from the databases search, 23 studies including 105,380 participants were eligible. Pooled analysis showed that higher uric acid levels significantly affected the risk of GDM (OR 2.58, 95% CI 1.89-3.52, I2  = 90.8%, P < 0.001). Subgroup analyses based on the gestational week showed that higher uric acid levels before the 20th week of gestation were significantly associated with the risk of GDM (OR 3.26, 95% CI 2.26-4.71, I2  = 89.3%, P < 0.001). Based on the meta-regression analysis, uric acid levels and odds of GDM were significantly correlated with the participants' age, and it was more significant in younger pregnant women.

CONCLUSIONS

This study showed a positive association between uric acid levels and the risk of GDM. Also, our results indicate that measuring uric acid levels before 20 weeks of gestation can potentially predict GDM, especially in younger women.

A 7-Step Guideline for Qualitative Synthesis and Meta-Analysis of Observational Studies in Health Sciences

Objectives: To provide a step-by-step, easy-to-understand, practical guide for systematic review and meta-analysis of observational studies. Methods: A multidisciplinary team of researchers with extensive experience in observational studies and systematic review and meta-analysis was established. Previous guidelines in evidence synthesis were considered. Results: There is inherent variability in observational study design, population, and analysis, making evidence synthesis challenging. We provided a framework and discussed basic meta-analysis concepts to assist reviewers in making informed decisions. We also explained several statistical tools for dealing with heterogeneity, probing for bias, and interpreting findings. Finally, we briefly discussed issues and caveats for translating results into clinical and public health recommendations. Our guideline complements "A 24-step guide on how to design, conduct, and successfully publish a systematic review and meta-analysis in medical research" and addresses peculiarities for observational studies previously unexplored. Conclusion: We provided 7 steps to synthesize evidence from observational studies. We encourage medical and public health practitioners who answer important questions to systematically integrate evidence from observational studies and contribute evidence-based decision-making in health sciences.

Hormonal Replacement Therapy and Risk of Thyroid Cancer in Women: A Meta-Epidemiological Analysis of Prospective Cohort Studies

Objectives

Many experimental studies have reported that female sex hormones involve thyroid cancer development because the incidence rate of thyroid cancer in women (TCW) is 3 times higher than in men. Three previous systematic reviews reporting no association between hormone replacement therapy (HRT) and TCW risk had the same search year of 2014. The aim was to reevaluate the association between HRT use and TCW risk using a meta-epidemiological study of prospective cohort studies.

Methods

The study preferentially used all studies selected by the existing systematic reviews and then secured an additional cohort from the list citing the studies. The selection criterion was defined as the prospective cohort study assessing the association between HRT and TCW risk by adjusted relative risk and its 95% confidence intervals (CI) from multivariate analysis. A random-effects model meta-analysis was applied to estimate summary relative risk (sRR) and its 95% CI. A publication bias was evaluated by Egger’s test; moreover, the statistical significance level was set at 5%.

Results

Nine cohort studies were finally selected. The random-effect model was applied because of heterogeneity (I² = 64.3%). The sRR and its 95% CI from a random-effects model meta-analysis had no statistical significance in the association between HRT and TCW risk (sRR = 1.11; 95% CI, 0.98–1.26). Additionally, Egger’s test revealed no statistical significance (P = 0.91).

Conclusions

HRT is not associated with TCW risk based on the random-effects model meta-analysis of prospective cohort studies published until now.

Association between Oral Hygiene and Metabolic Syndrome: A Systematic Review and Meta-Analysis

Emerging evidence has linked poor oral hygiene to metabolic syndrome (MetS), but previously, no summary of evidence has been conducted on the topic. This systematic review and meta-analysis aims to evaluate the associations of oral hygiene status and care with MetS. A systematic search of the PubMed and Web of Science databases from inception to 17 March 2021, and examination of reference lists was conducted to identify eligible observational studies. A random-effects model was applied to pool the effects of oral hygiene status and care on MetS. Thirteen studies met the inclusion criteria and had sufficient methodological quality. Good oral hygiene status (OR = 0.30 (0.13-0.66); I2 = 91%), frequent tooth brushing (OR = 0.68 (0.58-0.80); I2 = 89%), and frequent interdental cleaning (OR = 0.89 (0.81-0.99); I2 = 27%) were associated with a lower risk of MetS. Only one study examined the association between dental visits and MetS (OR = 1.10 (0.77-1.55)). Our findings suggested that there might be inverse associations of oral hygiene status, tooth-brushing frequency, and interdental cleaning with MetS. However, substantial heterogeneity for tooth-brushing frequency and inconsistent results for oral hygiene status in subgroup analyses were observed. There was insufficient evidence for the association between dental visits and MetS. Further longitudinal studies are needed to investigate these associations.

A systematic review and meta-analysis of the association between fish consumption and risk of metabolic syndrome

AIMS

Results regarding the association between fish intake and risk of metabolic syndrome (MetS) are ambiguous. Therefore, this study aims to evaluate whether there is an association between fish consumption and risk of MetS.

DATA SYNTHESIS

A comprehensive literature search was conducted of PubMed, Embase, ScienceDirect and Google Scholar up to August 2019. A random-effects model was used to pool the risk of MetS in the highest category of fish consumption compared with the lowest one. Subgroup analysis was conducted based on country of region, gender, dietary tool, MetS definition, energy adjustment and sample size. A dose-response of analysis of fish intake and risk of MetS was also conducted. Twelve studies with a total of 16 effect sizes (10 cross-sectional and six cohort) were included. An inverse association was observed between fish intake and risk of MetS in cohort (OR = 0.80, 95% CI: 0.66, 0.96; P = 0.017, I² = 62.9%) but not cross-sectional studies (OR = 0.80, 95% CI: 0.70, 1.02; P = 0.085, I² = 50.1%). Subgroup analysis suggested that the results were influenced by all the included variables but sample size. A significant non-linear association was observed between fish intake levels and risk of MetS (P-value for non-linearity = 0.010).

CONCLUSION

An inverse association existed between fish intake and risk of MetS when combining data from prospective cohort studies. Further studies are needed to confirm such an effect.

Dietary patterns and frailty: a systematic review and meta-analysis

CONTEXT

Assessing the relationship between single nutrients and frailty fails to take into consideration the interactions between nutrients. An increasing number of investigations in recent years have evaluated the association between dietary patterns and frailty.

OBJECTIVE

This systematic review and meta-analysis was conducted to summarize the association between dietary patterns and frailty.

DATA SOURCES

PubMed, Scopus, and Google Scholar were searched for epidemiological studies published up to April 2018 that assessed the association between dietary patterns and frailty.

STUDY SELECTION

Cohort or cross-sectional studies that examined dietary patterns via an a priori or an a posteriori method in relation to risk of frailty without considering any specific age range were included. Studies were excluded if they examined single nutrients, single foods, or single food groups.

DATA EXTRACTION

Pooled effect sizes of eligible studies and their corresponding 95%CIs were estimated using random-effects models. When publication bias was present, trim and fill analysis was conducted to adjust the pooled effect.

RESULTS

A total of 13 studies with 15 effect sizes were identified. Results from 9 cohort and cross-sectional studies were included in the meta-analysis. Higher adherence to a healthy dietary pattern was associated with lower odds of frailty (odds ratio = 0.69; 95%CI, 0.57-0.84; P < 0.0001; I2 =92.1%; P for heterogeneity < 0.0001).

CONCLUSIONS

The findings suggest that a diet high in fruit, vegetables, and whole grains may be associated with reduced risk of frailty. Nevertheless, additional longitudinal studies are needed to confirm the association of dietary patterns with frailty.

A systematic review and meta-analysis of the association between childhood infections and the risk of childhood acute lymphoblastic leukaemia

Background:

To determine whether childhood infections were associated with the development of childhood acute lymphoblastic leukaemia (ALL).

Methods:

We included studies that assessed any infection in childhood prior to the diagnosis of ALL in children aged 0–19 years compared to children without cancer. The primary analysis synthesised any infection against the odds of ALL, and secondary analyses assessed the frequency, severity, timing of infections, and specific infectious agents against the odds of ALL. Subgroup analyses by data source were investigated.

Results:

In our primary analysis of 12 496 children with ALL and 2 356 288 children without ALL from 38 studies, we found that any infection was not associated with ALL (odds ratio (OR)=1.10, 95% CI: 0.95–1.28). Among studies with laboratory-confirmed infections, the presence of infections increased the odds of ALL by 2.4-fold (OR=2.42, 95% CI: 1.54–3.82). Frequency, severity, and timing of infection were not associated with ALL.

Conclusions:

The hypothesis put forward by Greaves and others about an infectious aetiology are neither confirmed nor refuted and the overall evidence remains inadequate for good judgement. The qualitative difference in the subgroup effects require further study, and future research will need to address the challenges in measuring infectious exposures.