Role of DNA methylation in the relationship between glioma risk factors and glioma incidence: a two-step Mendelian randomization study

Genetic evidence suggests glioma risk is altered by leukocyte telomere length, allergic disease (asthma, hay fever or eczema), alcohol consumption, childhood obesity, low-density lipoprotein cholesterol (LDLc) and triglyceride levels. DNA methylation (DNAm) variation influences many of these glioma-related traits and is an established feature of glioma. Yet the causal relationship between DNAm variation with both glioma incidence and glioma risk factors is unknown. We applied a two-step Mendelian randomization (MR) approach and several sensitivity analyses (including colocalization and Steiger filtering) to assess the association of DNAm with glioma risk factors and glioma incidence. We used data from a recently published catalogue of germline genetic variants robustly associated with DNAm variation in blood (32,851 participants) and data from a genome-wide association study of glioma risk (12,488 cases and 18,169 controls, sub-divided into 6191 glioblastoma cases and 6305 non-glioblastoma cases). MR evidence indicated that DNAm at 3 CpG sites (cg01561092, cg05926943, cg01584448) in one genomic region (HEATR3) had a putative association with glioma and glioblastoma risk (False discovery rate [FDR] < 0.05). Steiger filtering provided evidence against reverse causation. Colocalization presented evidence against genetic confounding and suggested that differential DNAm at the 3 CpG sites and glioma were driven by the same genetic variant. MR provided little evidence to suggest that DNAm acts as a mediator on the causal pathway between risk factors previously examined and glioma onset. To our knowledge, this is the first study to use MR to appraise the causal link of DNAm with glioma risk factors and glioma onset. Subsequent analyses are required to improve the robustness of our results and rule out horizontal pleiotropy.

Healthy dietary patterns, foods, and risk of glioma: A systematic review and meta-analysis of observational studies

Background

Accumulating epidemiological evidence has shown the favorable associations between healthy dietary patterns and risk of glioma, although the results remain inconclusive.

Objective

We therefore carried out a systematic review and meta-analysis to summarize the evidence from previous published studies, and to clarify the effects of healthy dietary patterns, typical healthy foods on glioma.

Methods

PubMed, Web of Science, CNKI, and Wan fang data were searched from inception up to September 2022 for eligible studies. Two authors independently performed the literature search, study selection, data extraction, and quality assessment. Heterogeneity across studies was estimated using the Cochran's Q test and I ² statistic. According to heterogeneity, the fixed-effects model or random-effects model was selected to obtain the relative risk (RR) of the merger. Subgroup analysis, sensitivity analysis and publication bias were also used for our analysis.

Results

Twenty-four articles that met the selection criteria, involving 7,278 glioma cases and 2,143,528 participants, were included in our analysis. There was a reduced risk of glioma in the highest compared with the lowest categories of healthy dietary patterns (RR = 0.58; 95% CI: 0.44-0.77; P < 0.0001). Moreover, compared with the lowest intakes, the highest intakes of vegetables (RR = 0.84; 95% CI: 0.73-0.96; P = 0.012) and fruits (RR = 0.85; 95% CI: 0.72-1.00; P = 0.045) significantly reduce the risk of glioma. However, the intakes of fresh fish, nuts, whole grains, and dairy products showed no statistically significant associations with the risk of glioma (P > 0.05).

Conclusion

Findings from this systematic review and meta-analysis indicate that higher intakes of healthy dietary patterns, vegetables, and fruits are significantly associated with the lower risk of glioma. Further studies, particularly with prospective design, are required to confirm our findings.

Dietary total antioxidant capacity is inversely associated with the odds of non-alcoholic fatty liver disease in people with type-2 diabetes

BACKGROUND

This study was conducted to evaluate possible associations between Dietary Total Antioxidant Capacity (DTAC) and odds of non-alcoholic fatty liver disease (NAFLD) in people with type-2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

We recruited two hundred people with T2DM, and evaluated their liver steatosis using Fibroscan. Dietary intakes of participants were assessed using a validated food frequency questionnaire. DTAC was computed via ferric reducing antioxidant power (FRAP).

RESULTS

In the crude model, no statistically significant association was found between DTAC and the odds of NAFLD in people with diabetes. However, after adjustment for potential confounders including age, gender, diabetes duration, smoking status, physical activity, BMI, waist circumference, and energy, the most reduced adjusted OR was indicated for the third tertile vs. the first one (OR: 0.28, 95% CI: 0.09-0.81, P = 0.02), meaning that diabetic patients in the third tertile of DTAC had 72% decreased risk of NAFLD in comparison to those in the first one. The relationship was remained significant after additional adjustment for HOMA-IR, HbA1c, serum Triglyceride (TG), and low-density lipoprotein-cholesterol (LDL) levels (OR: 0.29, 95% CI: 0.09-0.93, P = 0.03). Importantly, a dose-response pattern was demonstrated for DTAC and risk of NAFLD (P = 0.04).

CONCLUSION

Higher DTAC was related with a decreased risk of NAFLD in individuals with diabetes.

Antioxidants in brain tumors: current therapeutic significance and future prospects

Brain cancer is regarded among the deadliest forms of cancer worldwide. The distinct tumor microenvironment and inherent characteristics of brain tumor cells virtually render them resistant to the majority of conventional and advanced therapies. Oxidative stress (OS) is a key disruptor of normal brain homeostasis and is involved in carcinogenesis of different forms of brain cancers. Thus, antioxidants may inhibit tumorigenesis by preventing OS induced by various oncogenic factors. Antioxidants are hypothesized to inhibit cancer initiation by endorsing DNA repair and suppressing cancer progression by creating an energy crisis for preneoplastic cells, resulting in antiproliferative effects. These effects are referred to as chemopreventive effects mediated by an antioxidant mechanism. In addition, antioxidants minimize chemotherapy-induced nonspecific organ toxicity and prolong survival. Antioxidants also support the prooxidant chemistry that demonstrate chemotherapeutic potential, particularly at high or pharmacological doses and trigger OS by promoting free radical production, which is essential for activating cell death pathways. A growing body of evidence also revealed the roles of exogenous antioxidants as adjuvants and their ability to reverse chemoresistance. In this review, we explain the influences of different exogenous and endogenous antioxidants on brain cancers with reference to their chemopreventive and chemotherapeutic roles. The role of antioxidants on metabolic reprogramming and their influence on downstream signaling events induced by tumor suppressor gene mutations are critically discussed. Finally, the review hypothesized that both pro- and antioxidant roles are involved in the anticancer mechanisms of the antioxidant molecules by killing neoplastic cells and inhibiting tumor recurrence followed by conventional cancer treatments. The requirements of pro- and antioxidant effects of exogenous antioxidants in brain tumor treatment under different conditions are critically discussed along with the reasons behind the conflicting outcomes in different reports. Finally, we also mention the influencing factors that regulate the pharmacology of the exogenous antioxidants in brain cancer treatment. In conclusion, to achieve consistent clinical outcomes with antioxidant treatments in brain cancers, rigorous mechanistic studies are required with respect to the types, forms, and stages of brain tumors. The concomitant treatment regimens also need adequate consideration.

A Meta-Analysis of Calcium Intake and Risk of Glioma

BACKGROUND

A meta-analysis was conducted to investigate the correlation between calcium intake and the risk of brain tumors (especially glioma).

METHODS

The PubMed, Web of Science, and Embase databases were searched for relevant papers on the association between calcium intake and glioma as of August 22, 2021. The odds ratio (OR) with a 95% confidence interval (CI) was calculated using a random-effects model. Egger's test was conducted to assess publication bias.

RESULTS

The meta-analysis includes four studies. The meta-analysis showed that calcium intake and the risk of brain tumors have a significant negative relationship (OR = 0.28; 95% CI: 0.11 to 0.72; P = 0.008). Dose-response analysis showed that for every 100 mg/day increase in calcium intake, the risk of glioma decreased by 7% (OR = 0.93; 95% CI: 0.88 to 0.98). In addition, compared with humans without calcium intake, when calcium intake is 455 mg/day, 800 mg/day and 1000 mg/day, the risk of glioma is 0.65 (95% CI 0.43, 0.97), 0.55 (95% CI 0.37, 0.82) and 0.37 (95% CI 0.15, 0.86).

CONCLUSION

There is a significant negative association between calcium intake and brain tumors (especially gliomas), but more high-quality studies are needed to verify these results.

Vitamin C intake and multiple health outcomes: an umbrella review of systematic reviews and meta-analyses

The purpose of this article was to assess the existing systematic reviews and meta-analyses for the association between vitamin C intake and multiple health outcomes. A total of 76 meta-analyses (51 papers) of randomised controlled trials and observational studies with 63 unique health outcomes were identified. Dose-response analysis showed that vitamin C intake was associated with reduced risk of all-cause mortality, cardiovascular disease (CVD), oesophageal cancer, gastric cancer, cervical cancer and lung cancer with an increment of 50-100 mg per day. Beneficial associations were also identified for respiratory, neurological, ophthalmologic, musculoskeletal, renal and dental outcomes. Harmful associations were found for breast cancer and kidney stones for vitamin C supplement intake. The benefits of vitamin C intake outweigh the disadvantages for a range of health outcomes. However, the recommendation of vitamin C supplements needs to be cautious. More prospective studies and well-designed randomised controlled trials (RCTs) are needed.

Vitamin C Intake and Cancers: An Umbrella Review

Based on the existing systematic reviews and meta-analyses, we conducted this umbrella review aiming at evaluating the quality of evidence, validity and biases of the relationship between vitamin C (VC) intake and incidence and outcomes of multiple cancers. We identified 22 cancer outcomes within 3,562 articles. VC consumption was associated with lower incidence of bladder cancer, breast cancer, cervical tumors, endometrial cancer, esophageal cancer, gastric cancer, glioma, lung cancer, pancreatic cancer, prostate cancer, renal cell cancer, and total cancer occurrence. VC intake was also related to decreased risk of breast cancer prognosis (recurrence, cancer-specific mortality, and all-cause mortality).

Exploring the Pivotal Neurophysiologic and Therapeutic Potentials of Vitamin C in Glioma

Gliomas represent solely primary brain cancers of glial cell or neuroepithelial origin. Gliomas are still the most lethal human cancers despite modern innovations in both diagnostic techniques as well as therapeutic regimes. Gliomas have the lowest overall survival rate compared to other cancers 5 years after definitive diagnosis. The dietary intake of vitamin C has protective effect on glioma risk. Vitamin C is an essential compound that plays a vital role in the regulation of lysyl and prolyl hydroxylase activity. Neurons store high levels of vitamin C via sodium dependent-vitamin C transporters (SVCTs) to protect them from oxidative ischemia-reperfusion injury. Vitamin C is a water-soluble enzyme, typically seen as a powerful antioxidant in plants as well as animals. The key function of vitamin C is the inhibition of redox imbalance from reactive oxygen species produced via the stimulation of glutamate receptors. Gliomas absorb vitamin C primarily via its oxidized dehydroascorbate form by means of GLUT 1, 3, and 4 and its reduced form, ascorbate, by SVCT2. Vitamin C is able to preserve prosthetic metal ions like Fe2+ and Cu+ in their reduced forms in several enzymatic reactions as well as scavenge free radicals in order to safeguard tissues from oxidative damage. Therapeutic concentrations of vitamin C are able to trigger H2O2 generation in glioma. High-dose combination of vitamin C and radiation has a much more profound cytotoxic effect on primary glioblastoma multiforme cells compared to normal astrocytes. Control trials are needed to validate the use of vitamin C and standardization of the doses of vitamin C in the treatment of patients with glioma.

A Case-Control Study on Dietary Acid Load in Relation to Glioma

Limited data are available linking dietary factors to glioma. The current study was conducted to investigate the association between Dietary Acid Load (DAL) and odds of glioma in Iranian adults. This case-control study was done on 128 newly diagnosed patients with glioma and 256 healthy controls in Tehran, Iran. A validated detailed food frequency questionnaire (FFQ) was used to assess dietary intakes of participants. DAL was estimated using the protein to potassium ratio (Pro: K). Glioma was diagnosed based on pathological tests. A detailed questionnaire including several non-dietary confounders was also completed. Participants in the highest tertile of DAL score had a non-significant higher odds of glioma as compared to those in the lowest tertile (OR: 1.50; 95% CI: 0.88-2.57), which remained after controlling for some potential confounders (OR: 1.66; 0.70-3.91). After further adjustment for dietary intakes of meats and processed meats, legumes and nuts, fruits, salt tea, and coffee, those in the top tertile of DAL score were significantly more likely to have glioma than those in the bottom tertile (OR: 3.09; 95% CI: 1.06, 8.99; P = 0.03). This association was also reached following further adjustment for BMI (OR: 3.05; 95% CI: 1.04, 8.91; P = 0.03). We found a significant positive association between dietary acid load, as estimated by Prot:K ratio, and odds of glioma among adults. Further studies, in particular prospective cohorts with long-term follow up, are required to confirm these findings.

A case-control study on dietary calcium intake and risk of glioma

Limited evidence exists regarding the association between dietary calcium intake and risk of glioma. The objective of this study was to determine the relationship between dietary calcium intake and risk of glioma in Iranian adults. In this hospital-based case-control study, we enrolled 128 newly-diagnosed cases of glioma and 256 age- and sex-matched controls. Patients with pathologically confirmed glioma (without any other cancers) were selected. Dietary intakes of study participants were collected through a validated 126-item food-frequency questionnaire. Dietary calcium intake was computed from dairy products in the questionnaire. Participants were categorized into quartiles of dietary calcium intake. Binary logistic regression was used to examine the association between dietary calcium intake and glioma. Higher dietary intake of calcium was associated with younger age, long duration of cell phone use, and frequent canned foods intake. After taking age, sex, and energy intake into account, participants with the greatest dietary calcium intake had 84% lower odds of glioma than those with the lowest intake [odds ratio (OR): 0.16; 95% confidence interval (CI), 0.07-0.37]. Further adjustment for other potential confounders including nutrient intakes did not significantly alter the association (OR: 0.22; 95% CI, 0.08-0.64). Even after additional adjustment for BMI, we found a significant inverse association between dietary calcium intake and odds of glioma (OR: 0.23; 95% CI, 0.08-0.65). We found an inverse protective association between high dietary calcium intake and odds of glioma. Further prospective cohort studies are needed to confirm these findings.

Dissecting the mechanism of temozolomide resistance and its association with the regulatory roles of intracellular reactive oxygen species in glioblastoma

Glioblastoma is the most common primary malignant brain tumor that is usually considered fatal even with treatment. This is often a result for tumor to develop resistance. Regarding the standard chemotherapy, the alkylating agent temozolomide is effective in disease control but the recurrence will still occur eventually. The mechanism of the resistance is various, and differs in terms of innate or acquired. To date, aberrations in O⁶-methylguanine-DNA methyltransferase are the clear factor that determines drug susceptibility. Alterations of the other DNA damage repair genes such as DNA mismatch repair genes are also known to affect the drug effect. Together these genes have roles in the innate resistance, but are not sufficient for explaining the mechanism leading to acquired resistance. Recent identification of specific cellular subsets with features of stem-like cells may have role in this process. The glioma stem-like cells are known for its superior ability in withstanding the drug-induced cytotoxicity, and giving the chance to repopulate the tumor. The mechanism is complicated to administrate cellular protection, such as the enhancing ability against reactive oxygen species and altering energy metabolism, the important steps to survive. In this review, we discuss the possible mechanism for these specific cellular subsets to evade cancer treatment, and the possible impact to the following treatment courses. In addition, we also discuss the possibility that can overcome this obstacle.

Vitamin C Transporters and Their Implications in Carcinogenesis

Vitamin C is implicated in various bodily functions due to its unique properties in redox homeostasis. Moreover, vitamin C also plays a great role in restoring the activity of 2-oxoglutarate and Fe²⁺ dependent dioxygenases (2-OGDD), which are involved in active DNA demethylation (TET proteins), the demethylation of histones, and hypoxia processes. Therefore, vitamin C may be engaged in the regulation of gene expression or in a hypoxic state. Hence, vitamin C has acquired great interest for its plausible effects on cancer treatment. Since its conceptualization, the role of vitamin C in cancer therapy has been a controversial and disputed issue. Vitamin C is transferred to the cells with sodium dependent transporters (SVCTs) and glucose transporters (GLUT). However, it is unknown whether the impaired function of these transporters may lead to carcinogenesis and tumor progression. Notably, previous studies have identified SVCTs’ polymorphisms or their altered expression in some types of cancer. This review discusses the potential effects of vitamin C and the impaired SVCT function in cancers. The variations in vitamin C transporter genes may regulate the active transport of vitamin C, and therefore have an impact on cancer risk, but further studies are needed to thoroughly elucidate their involvement in cancer biology.

The effects of chitosan-based materials on glioma: Recent advances in its applications for diagnosis and treatment

Glioma is known as the most common primary brain tumor occurring in adolescents and is considered as a lethal disease worldwide. Despite the advancements in presently available therapeutic approaches (i.e. radiation therapy and chemotherapy), the rate of amelioration in glioma patients is still low. In this regard, it seems that there is a need for reconsidering and enhancing current therapies and/or discovering novel therapeutic platforms. Chitosan is a natural polysaccharide with several beneficial characteristics, including biocompatibility, biodegradability, and low toxicity. Without causing toxic effects on healthy cells, chitosan nanoparticles are attractive targets in cancer therapy which lead to the sustained release and enhanced internalization of chemotherapeutic drugs as well as higher cytotoxicity for cancer cells. Hence, these properties turn it into a suitable candidate for the treatment of various cancers, including glioma. In the viewpoint of glioma, cancer inhibition is possible through targeting glioma-associated signaling pathways and molecules such as MMP-9, VEGF, TRAIL and nuclear factor-κB by chitosan and its derivatives. Moreover, it has been acknowledged that chitosan and its derivatives can be applied as a delivery system for carrying a diverse range of therapeutic agents to the tumor site. Besides the anti-glioma effects of chitosan and its derivatives, these molecules can be utilized for culturing glioma cancer cells; providing a better understanding of glioma pathogenesis. Furthermore, it is documented that 3D chitosan scaffolds are potential targets that offer advantageous drug screening platforms. Herein, we summarized the anti-glioma effects of chitosan and also its utilization as drug delivery systems in the treatment of glioma.

The Association between Dietary Total Antioxidant Capacity and Glioma in Adults

OBJECTIVE

We assessed the relation between dietary total antioxidant capacity (TAC) and risk of glioma among Iranian adults. Design: A hospital-based case-control study. Setting: This case-control investigation was done in 2011. Usual dietary intakes of participants during the preceding year were examined using a food frequency questionnaire. Data on dietary TAC from foods was gathered from published databases that provided the antioxidant capacity for each food item, measured by ferric reducing antioxidant power. Participants: Cases were individuals with pathologically confirmed glioma that were diagnosed during the last month (n = 128). Controls were individuals, aged between 20 and 75 years, who were hospitalized or were outpatients referred to other wards of the same hospitals (n = 256). Results: Compared with participants in the lowest quartile, those in the highest quartile of dietary TAC had a lower odds of glioma (OR: 0.28, 95%CI: 0.15-0.45). This association was strengthened when potential confounders were taken into account (OR: 0.13; 95%CI: 0.05-0.35). Such inverse association was also seen for men (OR: 0.05, 95%CI: 0.01-0.19), but not for women. Furthermore, significant inverse associations were seen between dietary intakes of vitamin C (OR for Q₄ vs. Q₁: 0.14, 95%CI: 0.05-0.36; P-trend < 0.01), vitamin B6 (OR for Q₄ vs. Q₁: 0.35, 95%CI: 0.13-0.97; P-trend = 0.02) and β-carotene (OR for Q₃ vs. Q₁: 0.43, 95%CI: 0.19-0.98; P-trend = 0.57) and glioma, after controlling for potential covariates. Conclusions: We found that dietary TAC as well as dietary intake of vitamin C, vitamin B6, and β-carotene was inversely associated with odds of glioma in adults.

Association between fish intake and glioma risk: a systematic review and meta-analysis

Objectives

We investigated the association between the consumption of fresh and processed fish and glioma risk using a meta-analysis approach.

Methods

We selected and analyzed observational studies that discussed the relationships between fresh and processed fish intake on glioma risk from PubMed, Web of Science, Embase, and the SinoMed and Wanfang databases from inception to 31 March 2020. Studies were selected according to pre-established eligibility criteria and data were extracted separately by two researchers. A meta-analysis was conducted based on a random-effects model to provide pooled odds ratios (OR) and 95% confidence intervals (CIs).

Results

Eight studies considered the relationship between fish intake (seven fresh and seven processed fish) and glioma risk and were included in this meta-analysis. The OR effect size for fresh fish intake and glioma risk was 0.72 (95%CI 0.53–0.97) and the overall OR effect size for processed fish intake and glioma risk was 1.88 (95%CI 1.06–3.34).

Conclusion

Dietary intake of fresh fish may reduce the risk of glioma, but consumption of processed fish may increase the risk of glioma. This study had some limitations, and further studies are therefore required to clarify the associations between fish intake and glioma risk.

The Influence of Nutritional and Lifestyle Factors on Glioma Incidence

Cancers are the first main cause of premature death in developed countries. Since brain tumors, especially gliomas, are the most lethal type of cancers, risk factors for their prevalence are still being discussed. Nearly 30–50% of all cancers could be prevented by proper nutritional habits and other lifestyle factors, but their influence on the tumors of the central nervous system has not been explained completely and still requires further studies. That is why we attempted to review the available research in this field, with a special focus on the factors with the proven protective activity observed in other cancers. Adequate vegetables and antioxidants (such as vitamins C and A) provided with a diet could have a protective effect, while other factors have shown no correlation with the incidence of glioma. However, further studies are necessary to determine whether fish, coffee, and tea consumption may prevent glioma. Maintaining proper body weight and undertaking a sufficient level of daily physical activity also seem to be important. Excessive body mass index (BMI) and higher attained height have increased the risk of glioma. In order to link more accurately the chosen factors to the prevalence of gliomas, it seems necessary to conduct large cohort, prospective, controlled studies in different world regions.

Adherence to the Mediterranean dietary pattern in relation to glioma: A case-control study

BACKGROUND

Although Mediterranean diet (MD) was associated with a lower risk of mortality and cancer, no data are available investigating the association between adherence to the MD and risk of glioma.

METHODS

In this case-control study, we enrolled a total of 128 newly diagnosed patients with glioma, confirmed by pathological assessment, and 256 hospital-based controls from 2009 to 2011 in Tehran, Iran. A valid and reliable Block-format food frequency questionnaire (FFQ) was used to assess dietary intakes. Adherence to the MD was examined using the scoring method suggested by Trichopoulou et al. Logistic regression was used to examine the associations of interest.

RESULTS

After controlling for age, sex, and energy intake, participants in the highest tertile of MD score had not significantly lower odds of glioma than those in the lowest tertile (OR: 0.58, 95% CI: 0.32-1.03, P_trend = 0.06). However, after taking other potential confounders into account, individuals with the greatest adherence to the MD score were 74% less likely to have glioma than those with the lowest adherence (OR: 0.26, 95% CI: 0.12-0.55, P_trend < 0.001). Additional adjustments for dietary intakes and BMI did not significantly alter this association (OR: 0.36, 95% CI: 0.16-0.78, P_trend = 0.009; OR: 0.36, 95% CI: 0.16-0.78, P_trend = 0.01, respectively).

CONCLUSION

We found that adherence to the MD was associated with a lower likelihood of having glioma. Prospective cohort studies are needed to further examine these findings.

Testing for causality between systematically identified risk factors and glioma: a Mendelian randomization study

BACKGROUND

Whilst epidemiological studies have provided evidence of associations between certain risk factors and glioma onset, inferring causality has proven challenging. Using Mendelian randomization (MR), we assessed whether associations of 36 reported glioma risk factors showed evidence of a causal relationship.

METHODS

We performed a systematic search of MEDLINE from inception to October 2018 to identify candidate risk factors and conducted a meta-analysis of two glioma genome-wide association studies (5739 cases and 5501 controls) to form our exposure and outcome datasets. MR analyses were performed using genetic variants to proxy for candidate risk factors. We investigated whether risk factors differed by subtype diagnosis (either glioblastoma (n = 3112) or non-glioblastoma (n = 2411)). MR estimates for each risk factor were determined using multiplicative random effects inverse-variance weighting (IVW). Sensitivity analyses investigated potential pleiotropy using MR-Egger regression, the weighted median estimator, and the mode-based estimator. To increase power, trait-specific polygenic risk scores were used to test the association of a genetically predicated increase in each risk factor with glioma onset.

RESULTS

Our systematic search identified 36 risk factors that could be proxied using genetic variants. Using MR, we found evidence that four genetically predicted traits increased risk of glioma, glioblastoma or non-glioblastoma: longer leukocyte telomere length, liability to allergic disease, increased alcohol consumption and liability to childhood extreme obesity (> 3 standard deviations from the mean). Two traits decreased risk of non-glioblastoma cancers: increased low-density lipoprotein cholesterol (LDLc) and triglyceride levels. Our findings were similar across sensitivity analyses that made allowance for pleiotropy (genetic confounding).

CONCLUSIONS

Our comprehensive investigation provides evidence of a causal link between both genetically predicted leukocyte telomere length, allergic disease, alcohol consumption, childhood extreme obesity, and LDLc and triglyceride levels, and glioma. The findings from our study warrant further research to uncover mechanisms that implicate these traits in glioma onset.

Legume and Nuts Consumption in Relation to Glioma: A Case- Control Study

Data on the link between legume and nuts consumption and risk of glioma are controversial. The current study aimed to investigate the relation between legume and nuts consumption and glioma in a case-control study in Iranian adults. In this hospital-based case-control study, we enrolled 128 pathologically confirmed new cases of glioma and 256 age and sex-matched controls. Dietary intakes of study participants were assessed using the validated Block-format 123-item semi-quantitative FFQ. Data on potential confounders were also collected through the use of a pre-tested questionnaire. Mean age of cases and controls were 43.4 and 42.8 years, respectively. Individuals with the greatest legume and nuts consumption were less likely to have glioma compared with those with the lowest consumption (0.52; 95% CI: 0.30-0.88). This inverse association was not changed after controlling for age, sex and energy intake (0.46; 95% CI: 0.26-0.81). The association remained statistically significant even after taking other potential confounders, including dietary intakes into account (0.32; 95% CI: 0.14-0.72). Additional adjustments for BMI did not alter the association; such that individuals in the top category of legume and nuts consumption were 66% less likely to have glioma compared with those in the bottom category (0.34; 95% CI: 0.15-0.76). We found an inverse association between legume and nuts consumption and odds of glioma, even after controlling for a wide range of confounders.

A case–control study on dietary quality indices and glioma

No study is available that has assessed the association of dietary diversity score (DDS) and alternative healthy eating index (AHEI) with glioma. The present study aimed to assess this association in Iranian adults. Overall, 128 pathologically confirmed cases of glioma were enrolled from hospitals and 256 age- and sex-matched controls were recruited from other wards of the hospital between 2009 and 2011. Dietary assessment was done using a validated block-format 123-item semi-quantitative FFQ. Dietary indices including DDS and AHEI-2010 were constructed according to standard methods. After controlling for potential confounders, a significant inverse association was found between DDS and risk of glioma (OR 0·42, 95 % CI 0·19, 0·94). Such finding was also seen when further adjustment was made for BMI; such that participants in the highest quartile of DDS were 56 % less likely to have glioma compared with those in the lowest quartile (OR 0·44, 95 % CI, 0·20, 0·97). In addition, a significant inverse association was found between adherence to AHEI and glioma; such that in the fully adjusted model, participants in the fourth quartile of AHEI had 74 % lower risk of glioma compared with those in the first quartile (OR 0·26, 95 % CI 0·12, 0·56). In conclusion, we found that greater adherence to the healthy, as measured by AHEI, and diverse, as measured by DDS, diets was associated with decreased odds of glioma.

Association between tea and coffee consumption and brain cancer risk: an updated meta-analysis

Background

Previous studies had demonstrated some associations between coffee and tea consumption and brain cancer risk resulted in an inconsistent relationship. We therefore performed this study to further explore the association between them.

Method

By searching PubMed, Embase, and Web of Science, we retrieved up to 1 November 2018, 11 relevant literature of publications were collected by 2 people eventually. Stata 14.0 software was used for data analysis.

Results

In total, 11 articles (11 articles for coffee, 8 articles for tea, and 4 articles for coffee plus tea) were used in this meta-analysis. A statistically significant protective effect of coffee consumption and brain cancer risk was found (RR = 0.785, 95% CI = 0.580–0.984, I² = 65.6%, P_{for heterogeneity} = 0.001), especially in Asian populations (RR = 0.217, 95% CI = 0.042–0.896). However, the association between the risk of brain cancer and tea consumption was non-significant in the whole result (RR = 0.897, 95% CI = 0.739–1.088, I² = 29.9%, P_{for heterogeneity} = 0.189), but significant in American populations (RR = 0.798, 95% CI = 0.646–0.986). Interestingly, the RR was 0.684 (95% CI = 0.481–0.975) for the risk of brain cancer when compared the highest versus the lowest category consumption of coffee plus tea.

Conclusion

Findings from this study suggested that higher consumption of coffee may contribute to the lower development of brain cancer in Asian populations. Tea consumption had an inverse association for the risk of brain cancer in American populations, instead of other populations.

Electronic supplementary material

The online version of this article (10.1186/s12957-019-1591-y) contains supplementary material, which is available to authorized users.

Use of Mendelian andomization for dentifying isk actors for rain umors

Gliomas are a group of primary brain tumors, the most common and aggressive subtype of which is glioblastoma. Glioblastoma has a median survival of just 15 months after diagnosis. Only previous exposure to ionizing radiation and particular inherited genetic syndromes are accepted risk factors for glioma; the vast majority of cases are thought to occur spontaneously. Previous observational studies have described associations between several risk factors and glioma, but studies are often conflicting and whether these associations reflect true casual relationships is unclear because observational studies may be susceptible to confounding, measurement error and reverse causation. Mendelian randomization (MR) is a form of instrumental variable analysis that can be used to provide supporting evidence for causal relationships between exposures (e.g., risk factors) and outcomes (e.g., disease onset). MR utilizes genetic variants, such as single nucleotide polymorphisms (SNPs), that are robustly associated with an exposure to determine whether there is a causal effect of the exposure on the outcome. MR is less susceptible to confounding, reverse causation and measurement errors as it is based on the random inheritance during conception of genetic variants that can be relatively accurately measured. In previous studies, MR has implicated a genetically predicted increase in telomere length with an increased risk of glioma, and found little evidence that obesity related factors, vitamin D or atopy are causal in glioma risk. In this review, we describe MR and its potential use to discover and validate novel risk factors, mechanistic factors, and therapeutic targets in glioma.

Dietary Polyunsaturated Fat Intake in Relation to Glioma: A Case-Control Study

This study aimed to assess the association of dietary polyunsaturated fatty acid (PUFA) and risk of glioma among the Iranian population. A case-control study carried out among 128 newly diagnosed glioma adult patients with pathologically confirmed samples along with 256 sex- and age-matched controls. Dietary intake was examined by means of a validated semiquantitative food frequency questionnaire (FFQ). Total PUFA intake was computed by summing up dietary PUFAs from all food items in the questionnaire. Participants were categorized based on quartile cut-points of dietary PUFA intake. After taking into account the effect of age, sex and energy intake, individuals in the top quartile of PUFA intake were 77% less likely to have glioma than those in the bottom quartile (OR: 0.23; 95% CI: 0.11-0.48). Further adjustment for other potential variables strengthened the association. Additional controlling of nutrients did not alter the findings (OR: 0.19; 95% CI: 0.04-0.78). When we took into account the effect of body mass index (BMI), we found those in the highest quartile of PUFA intake has lower odds of glioma than those in the lowest (OR: 0.20; 95% CI: 0.05-0.84). We found dietary PUFA intake was inversely associated with risk of glioma in this case-control study on Iranian adults.

Micronutrient Intake and Risk of Hematological Malignancies in Adults: A Systematic Review and Meta-analysis of Cohort Studies

There has been accumulating evidence that several micronutrients may play a protective role in the risk of solid cancers. However, their role in hematological malignancies remains to be elucidated; this meta-analysis aims to evaluate the associations between micronutrient intake as well as supplementation and risk of hematological cancer in adults. Eligible cohort studies (examining intake of vitamin A, vitamin C, vitamin D, vitamin E, lycopene, folate, iron, carotenoids, beta-carotene, selenium, pyridoxine) were sought in PubMed up to July 31, 2016. Random-effects models were used for the calculation of pooled relative risks (RR) with their 95% confidence intervals (CI). Twelve cohort studies were deemed eligible. Null associations were noted regarding supplemented vitamin A (pooled relative risk [RR] = 0.92, 95% confidence interval [CI]: 0.80-1.07), supplemented vitamin C (pooled RR = 1.00, 95%CI: 0.90-1.12), total vitamin D (pooled RR = 1.05, 95%CI: 0.91-1.20), supplemented vitamin E (pooled RR = 0.98, 95%CI: 0.88-1.10), and dietary lycopene intake (pooled RR = 1.00, 95%CI: 0.86-1.16) and the risk of non-Hodgkin lymphoma. No summary estimates are provided for other hematological malignancies due to the limited number of studies. Future prospective trials should be conducted for a better understanding of this field; especially regarding Hodgkin lymphoma, leukemia and plasma cell neoplasms, on which data are scarce.

The Association Between Index of Nutritional Quality (INQ) and Glioma and Evaluation of Nutrient Intakes of These Patients: A Case-Control Study

INTRODUCTION

Glioma is the most common adult brain tumors. Dietary factors may play a role in the etiology of glioma. The Index of Nutritional Quality (INQ) provides a general overview for the nutrient content of a food or a diet. This study aimed to investigate the association between INQ and glioma and nutrient intakes.

MATERIAL AND METHODS

This study was included 128 patients and 256 controls. Dietary intakes of the subjects were evaluated by a food frequency questionnaire (FFQ) and FFQ-derived dietary data were used to calculate INQ scores. Logistic regression was used to calculate the odds ratios and 95% confidence intervals.

RESULTS

Cases had higher intake of total fat, saturated fatty acid (SFA), meats, hydrogenated oils and controls had higher intake of monounsaturated fatty acid, polyunsaturated fatty acid, calcium, dairy, fruits, and nuts. Only the INQ of vitamin C, vitamin E, calcium, and fiber are higher in controls. An inverse association was observed between glioma and INQ of calcium, vitamin E, vitamin C, and fiber.

CONCLUSION

The results of this study propose a healthy diet such as high intake of vitamins C and E, calcium, fiber, food groups like fruits and vegetables, and low-fat milk and nuts; and low consumption of total fat, SFA, and red meat may be protective against glioma.

Tea and coffee consumption in relation to glioma: a case-control study

PURPOSE

Data on the link between tea and coffee consumption and risk of glioma are controversial. We aimed to examine the association between tea and coffee consumption and glioma in Iranian adults.

METHODS

In this hospital-based case-control study, we enrolled 128 pathologically confirmed new cases of glioma and 256 age- and sex-matched controls. Dietary intakes of study participants including tea and coffee consumption was assessed using the validated Block-format 123-item semi-quantitative FFQ. Participants were categorized based on tertiles of tea and coffee consumption. Data on potential confounders were also collected through the use of pre-tested questionnaire.

RESULTS

Individuals with the greatest tea consumption were less likely to have glioma compared with those with the lowest consumption (0.36; 0.20-0.68). This inverse association was not changed after controlling for energy intake. The association remained statistically significant even after taking other potential confounders, including dietary intakes of red and processed meats, legumes and nuts, fruits, salt and mutual effects of tea and coffee consumption, into account (0.33; 0.13-0.86). Additional adjustments for BMI did not alter the association. After controlling for potential confounders, including dietary intakes and BMI, coffee consumption was inversely associated with odds of glioma; such that individuals in the top category of coffee consumption were 91% less likely to have glioma compared with those in the bottom category (0.09; 0.03-0.24). Considering coffee and tea intake combined, those in the highest tertile were 65% less likely to have glioma compared with those in the lowest tertile (0.35; 0.15-0.83).

CONCLUSION

We found an inverse association between tea and coffee consumption and odds of glioma, even after controlling for a wide range of confounders.

Association between Dietary Vitamin A Intake and the Risk of Glioma: Evidence from a Meta-analysis

The results from epidemiological studies between dietary vitamin A intake and glioma risk is not consistent. Thus, a meta-analysis was conducted to confirm the exact relationship between them. PubMed and Web of Knowledge were used to search the relevant articles up to May 2015. Pooled relative risk (RR) with 95% confidence interval (CI)was calculated using random-effect model. Egger’s test was used to assess the small-study effect. At the end, seven articles with eight case-control studies involving 1841 glioma cases and 4123 participants were included. Our study indicated that highest category of dietary vitamin A intake was significantly associated with reduced risk of glioma (RR = 0.80, 95% CI = 0.62–0.98, p = 0.014, I² = 54.9%). Egger’s test did not find any publication bias. In conclusion, our study indicated that higher category of dietary vitamin A intake could reduce the glioma risk. However, we could not do a dose-response analysis for vitamin A intake with glioma risk due to the limited data in each reported individual article. Due to this limitation, further studies with detailed dose, cases and person-years for each category is wanted to assess this dose-response association.