Unintended Side Effects of Electronic Cigarettes in Otolaryngology: A Scoping Review

Recent Emergence ◽

Scoping Reviews ◽

Long Term Impact ◽

Objective Electronic cigarettes (E-cigs) are nicotine delivery systems with increasing popularity. The US Food and Drug Administration defines side effects as unwanted or unexpected events or reactions. Our objective was to examine the unintended otolaryngology-related side effects associated with E-cigs. Data Sources Medline, EMBASE, CINAHL, Web of Science, and CENTRAL databases. Review Methods Study selection was independently performed by 2 authors in accordance with the PRISMA-ScR statement (Preferred Reporting Items for Systematic Reviews and Meta-analyses Extension for Scoping Reviews); discrepancies were resolved by the senior author. English studies from database inception to May 1, 2020, with a sample size >5 were included. In vitro, animal, and lower respiratory tract studies were excluded. The main outcome was defined as otolaryngology-related side effects following E-cig use. Levels of evidence per the Oxford Centre for Evidence-Based Medicine were used to determine study quality. Results From 1788 articles, 32 studies were included. The most common unintended side effects were throat irritation (n = 16), cough (n = 16), mouth irritation (n = 11), and oral mucosal lesions (n = 8). A large proportion of participants also reported conventional tobacco use in addition to E-cigs. Eight studies investigated the effectiveness of vaping on smoking cessation. The quality of the literature was level 2 to 4. Given the significant heterogeneity in the studies, meta-analysis was not performed. Conclusion The most reported side effects were throat and mouth irritation, followed by cough. The long-term impact of E-cigs is not known given the recent emergence of this technology. Future studies are warranted.

Systematic Review: Allogenic Use of Stromal Vascular Fraction (SVF) and Decellularized Extracellular Matrices (ECM) as Advanced Therapy Medicinal Products (ATMP) in Tissue Regeneration

International Journal of Molecular Sciences ◽

10.3390/ijms21144982 ◽

2020 ◽

Vol 21 (14) ◽

pp. 4982 ◽

Cited By ~ 1

Author(s):

Pietro Gentile ◽

Aris Sterodimas ◽

Jacopo Pizzicannella ◽

Laura Dionisi ◽

Domenico De Fazio ◽

...

Keyword(s):

Systematic Review ◽

Meta Analysis ◽

Stromal Vascular Fraction ◽

Lateral Epicondylitis ◽

Medicinal Products ◽

Advanced Therapy Medicinal Products ◽

Advanced Therapy ◽

Meta Analyses ◽

Clinical Experiments

Stromal vascular fraction (SVF) containing adipose stem cells (ASCs) has been used for many years in regenerative plastic surgery for autologous applications, without any focus on their potential allogenic role. Allogenic SVF transplants could be based on the possibility to use decellularized extracellular matrix (ECM) as a scaffold from a donor then re-cellularized by ASCs of the recipient, in order to develop the advanced therapy medicinal products (ATMP) in fully personalized clinical approaches. A systematic review of this field has been realized in accordance with the Preferred Reporting for Items for Systematic Reviews and Meta-Analyses-Protocols (PRISMA-P) guidelines. Multistep research of the PubMed, Embase, MEDLINE, Pre-MEDLINE, PsycINFO, CINAHL, Clinicaltrials.gov, Scopus database, and Cochrane databases has been conducted to identify articles and investigations on human allogenic ASCs transplant for clinical use. Of the 341 articles identified, 313 were initially assessed for eligibility on the basis of the abstract. Of these, only 29 met all the predetermined criteria for inclusion according to the PICOS (patients, intervention, comparator, outcomes, and study design) approach, and 19 have been included in quantitative synthesis (meta-analysis). Ninety-one percent of the studies previously screened (284 papers) were focused on the in vitro results and pre-clinical experiments. The allogenic use regarded the treatment of perianal fistulas, diabetic foot ulcers, knee osteoarthritis, acute respiratory distress syndrome, refractory rheumatoid arthritis, pediatrics disease, fecal incontinence, ischemic heart disease, autoimmune encephalomyelitis, lateral epicondylitis, and soft tissue defects. The information analyzed suggested the safety and efficacy of allogenic ASCs and ECM transplants without major side effects.

Prevalence and Impact of Biofilms on Bloodstream and Urinary Tract Infections: A Systematic Review and Meta-Analysis

Antibiotics ◽

10.3390/antibiotics10070825 ◽

2021 ◽

Vol 10 (7) ◽

pp. 825

Author(s):

Henrique Pinto ◽

Manuel Simões ◽

Anabela Borges

Keyword(s):

Urinary Tract ◽

Urinary Tract Infections ◽

Meta Analysis ◽

Candida Spp ◽

Treatment Interventions ◽

Statistical Confidence ◽

Resistant Strains ◽

Meta Analyses ◽

Tract Infections

This study sought to assess the prevalence and impact of biofilms on two commonly biofilm-related infections, bloodstream and urinary tract infections (BSI and UTI). Separated systematic reviews and meta-analyses of observational studies were carried out in PubMed and Web of Sciences databases from January 2005 to May 2020, following PRISMA protocols. Studies were selected according to specific and defined inclusion/exclusion criteria. The obtained outcomes were grouped into biofilm production (BFP) prevalence, BFP in resistant vs. susceptible strains, persistent vs. non-persistent BSI, survivor vs. non-survivor patients with BSI, and catheter-associated UTI (CAUTI) vs. non-CAUTI. Single-arm and two-arm analyses were conducted for data analysis. In vitro BFP in BSI was highly related to resistant strains (odds ratio-OR: 2.68; 95% confidence intervals-CI: 1.60–4.47; p < 0.01), especially for methicillin-resistant Staphylococci. BFP was also highly linked to BSI persistence (OR: 2.65; 95% CI: 1.28–5.48; p < 0.01) and even to mortality (OR: 2.05; 95% CI: 1.53–2.74; p < 0.01). Candida spp. was the microorganism group where the highest associations were observed. Biofilms seem to impact Candida BSI independently from clinical differences, including treatment interventions. Regarding UTI, multi-drug resistant and extended-spectrum β-lactamase-producing strains of Escherichia coli, were linked to a great BFP prevalence (OR: 2.92; 95% CI: 1.30–6.54; p < 0.01 and OR: 2.80; 95% CI: 1.33–5.86; p < 0.01). More in vitro BFP was shown in CAUTI compared to non-CAUTI, but with less statistical confidence (OR: 2.61; 95% CI: 0.67–10.17; p < 0.17). This study highlights that biofilms must be recognized as a BSI and UTI resistance factor as well as a BSI virulence factor.

Alternative Tendon Coaptations to the Pulvertaft Weave Technique: A Systematic Review and Meta-Analysis of Biomechanical Studies

Hand ◽

10.1177/15589447211043213 ◽

2021 ◽

pp. 155894472110432

Author(s):

Emily M. Graham ◽

Jeremie D. Oliver ◽

Russell Hendrycks ◽

Dino Maglic ◽

Shaun D. Mendenhall

Keyword(s):

Systematic Review ◽

Yield Strength ◽

Random Effects ◽

Meta Analysis ◽

Dichotomous Data ◽

Inverse Variance ◽

Significant Difference ◽

Alternative Techniques ◽

Background The Pulvertaft weave technique (PT) is frequently used during tendon repairs and transfers. However, this technique is associated with limitations. In this systematic review and meta-analysis, quantitative and qualitative analyses were performed on in vitro, biomechanical studies that compared the PT with alternative techniques. Methods Articles included for qualitative and/or qualitative analysis were identified following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Studies included in the meta-analysis were analyzed either as continuous data with inverse variance and random effects or as dichotomous data using a Mantel-Haenszel analysis assuming random effects to calculate an odds ratio. Results A comprehensive electronic search yielded 8 studies meeting inclusion criteria for meta-analysis. Two studies with a total of 65 tendon coaptations demonstrated no significant difference in strength between the PT and traditional side-to-side (STS) techniques ( P = .92). Two studies with a total of 43 tendon coaptations showed that the STS with 1 weave has a higher yield strength than the PT ( P = .03). Two studies with a total of 62 tendon repairs demonstrated no significant difference in strength between the PT and the step-cut (SC) techniques ( P = .70). The final 2 studies included 46 tendon repairs and demonstrated that the wrap around (WA) technique has a higher yield strength than the PT ( P < .001). Conclusions The STS, SC, and WA techniques are preferred for improving tendon form. The STS and WA techniques have superior yield strengths than the PT, and the SC technique withstands similar stress to failure as the PT.

Effectiveness of Electronic Cigarettes in Smoking Cessation: A Systematic Review and Meta-analysis

Nicotine & Tobacco Research ◽

10.1093/ntr/ntaa181 ◽

2020 ◽

Cited By ~ 4

Author(s):

Igor Grabovac ◽

Moritz Oberndorfer ◽

Jismy Fischer ◽

Winfried Wiesinger ◽

Sandra Haider ◽

...

Keyword(s):

Systematic Review ◽

Smoking Cessation ◽

Random Effects ◽

Electronic Cigarettes ◽

Meta Analysis ◽

Current Evidence ◽

Quality Of Evidence ◽

Registration Number ◽

Abstract Introduction Reports of the effectiveness of e-cigarettes (ECs) for smoking cessation vary across different studies making implementation recommendations hard to attain. We performed a systematic review and meta-analysis to assess the current evidence regarding effectiveness of ECs for smoking cessation. Methods PubMed, PsycInfo, and Embase databases were searched for randomized controlled trials comparing nicotine ECs with non-nicotine ECs or with established smoking cessation interventions (nicotine replacement therapy [NRT] and or counseling) published between 1 January 2014 and 27 June 2020. Data from eligible studies were extracted and used for random-effects meta-analyses (PROSPERO registration number: CRD42019141414). Results The search yielded 13 950 publications with 12 studies being identified as eligible for systematic review (N = 8362) and 9 studies for random-effects meta-analyses (range: 30–6006 participants). The proportion of smokers achieving abstinence was 1.71 (95 CI: 1.02–2.84) times higher in nicotine EC users compared with non-nicotine EC users. The proportion of abstinent smokers was 1.69 (95 CI: 1.25–2.27) times higher in EC users compared with participants receiving NRT. EC users showed a 2.04 (95 CI: 0.90–4.64) times higher proportion of abstinent smokers in comparison with participants solely receiving counseling. Conclusions Our results suggest that nicotine ECs may be more effective in smoking cessation when compared with placebo ECs or NRT. When compared with counseling alone, nicotine ECs are more effective short term, but its effectiveness appears to diminish with later follow-ups. Given the small number of studies, heterogeneous design, and the overall moderate to low quality of evidence, it is not possible to offer clear recommendations. Implications The results of this study do not allow for a conclusive argument. However, pooling current evidence points toward a potential for ECs as a smoking cessation tool. Though, given the overall quality of evidence, future studies should aim for more clarity in terms of interventions and larger study populations.

Meta-Analysis to Evaluate the Role of Interferon in Follicular Lymphoma

Journal of Clinical Oncology ◽

10.1200/jco.2005.06.146 ◽

2005 ◽

Vol 23 (10) ◽

pp. 2215-2223 ◽

Cited By ~ 136

Author(s):

A.Z.S. Rohatiner ◽

W.M. Gregory ◽

B. Peterson ◽

E. Borden ◽

P. Solal-Celigny ◽

...

Keyword(s):

Follicular Lymphoma ◽

Response Rate ◽

Meta Analysis ◽

Phase Iii ◽

Newly Diagnosed ◽

Remission Duration ◽

Significant Difference ◽

Purpose To determine whether interferon (IFN) -α2, when given with or following chemotherapy, influences response rate, remission duration, and survival in newly diagnosed patients with follicular lymphoma. Patients and Methods Ten phase III studies evaluating the role of IFN-α2 in 1,922 newly diagnosed patients with follicular lymphoma were analyzed. Updated individual patient data were used to perform meta-analyses for response, survival, and remission duration. Results The addition of IFN-α2 to initial chemotherapy did not significantly influence response rate. An overall meta-analysis for survival showed a significant difference in favor of IFN-α2, but also showed significant heterogeneity between studies. Further analyses were carried out in order to explain this heterogeneity, and to define the circumstances in which IFN-α2 prolonged survival. The survival advantage was seen when IFN-α2 was given: (1) in conjunction with relatively intensive initial chemotherapy (2P = .00005), (2) at a dose ≥ 5 million units (2P = .000002), (3) at a cumulative dose ≥ 36 million units per month (2P = .000008), and (4) with chemotherapy rather than as maintenance therapy (P = .004). With regard to remission duration, there was also a significant difference in favor of IFN-α2, irrespective of the intensity of chemotherapy used, IFN dose, or whether IFN was given as a maintenance strategy or with chemotherapy. Conclusion When given in the context of relatively intensive initial chemotherapy, and at a dose ≥ 5 million units (≥ 36 × 106 units per month), IFN-α2 prolongs survival and remission duration in patients with follicular lymphoma.

Diagnosis of Schistosoma Infection in Non-Human Animal Hosts: A Systematic Review and Meta-Analysis

10.20944/preprints202105.0075.v1 ◽

2021 ◽

Author(s):

Song Liang ◽

Keerati Ponpetch ◽

Yi-Biao Zhou ◽

Jia-Gang Guo ◽

Berhanu Erko ◽

...

Keyword(s):

Systematic Review ◽

Meta Analysis ◽

Quantitative Polymerase Chain Reaction ◽

Diagnostic Techniques ◽

Molecular Technique ◽

Animal Hosts ◽

Polymerase Chain ◽

Human Animal ◽

Background Reliable and field-applicable diagnosis of schistosome infections in non-human animals is important for surveillance, control, and verification of interruption of human schistosomiasis transmission. This study aimed to summarize uses of available diagnostic techniques through a systematic review and meta-analysis. Methods and principal findings We systematically searched the literature and reports comparing two or more diagnostic tests in non-human animals for schistosome infection. Out of 4,909 articles and reports screened, 18 met our inclusion criteria, four of which were considered in the meta-analysis. A total of 14 techniques (parasitologic, immunologic, and molecular) and nine types of non-human animals were involved in the studies. Notably, four studies compared parasitologic tests (miracidium hatching test (MHT), Kato-Katz (KK), the Danish Bilharziasis Laboratory technique (DBL), and formalin-ethyl acetate sedimentation-digestion (FED-SD)) with quantitative polymerase chain reaction (qPCR), and sensitivity estimates (using qPCR as the reference) were extracted and included in the meta-analyses, showing significant heterogeneity across studies and animals hosts. The pooled estimate of sensitivity was 0.21 (95% confidence interval (CI): 0.03 – 0.48) with FED-SD showing highest sensitivity (0.89, 95% CI: 0.65 – 1.00). Conclusions and significance Our findings suggest that the parasitologic technique FEA-SD and the molecular technique, qPCR, are the most promising field-applicable techniques for schistosome diagnosis in non-human animal hosts. Future studies are needed for validation and standardization of the techniques for real-world field applications.

Dynamics of sputum conversion during effective tuberculosis treatment: A systematic review and meta-analysis

PLoS Medicine ◽

10.1371/journal.pmed.1003566 ◽

2021 ◽

Vol 18 (4) ◽

pp. e1003566

Author(s):

Claire J. Calderwood ◽

James P. Wilson ◽

Katherine L. Fielding ◽

Rebecca C. Harris ◽

Aaron S. Karat ◽

...

Keyword(s):

Systematic Review ◽

Data Extraction ◽

Meta Analysis ◽

World Health ◽

Tb Treatment ◽

Health Organization ◽

Reported Data ◽

Meta Analyses ◽

Culture Conversion

Background Two weeks’ isolation is widely recommended for people commencing treatment for pulmonary tuberculosis (TB). The evidence that this corresponds to clearance of potentially infectious tuberculous mycobacteria in sputum is not well established. This World Health Organization–commissioned review investigated sputum sterilisation dynamics during TB treatment. Methods and findings For the main analysis, 2 systematic literature searches of OvidSP MEDLINE, Embase, and Global Health, and EBSCO CINAHL Plus were conducted to identify studies with data on TB infectiousness (all studies to search date, 1 December 2017) and all randomised controlled trials (RCTs) for drug-susceptible TB (from 1 January 1990 to search date, 20 February 2018). Included articles reported on patients receiving effective treatment for culture-confirmed drug-susceptible pulmonary TB. The outcome of interest was sputum bacteriological conversion: the proportion of patients having converted by a defined time point or a summary measure of time to conversion, assessed by smear or culture. Any study design where more than 10 participants were included was considered. Record sifting and data extraction were performed in duplicate. Random effects meta-analyses were performed. A narrative summary additionally describes the results of a systematic search for data evaluating infectiousness from humans to experimental animals (PubMed, all studies to 27 March 2018). Other evidence on duration of infectiousness—including studies reporting on cough dynamics, human tuberculin skin test conversion, or early bactericidal activity of TB treatments—was outside the scope of this review. The literature search was repeated on 22 November 2020, at the request of the editors, to identify studies published after the previous censor date. Four small studies reporting 3 different outcome measures were identified, which included no data that would alter the findings of the review; they are not included in the meta-analyses. Of 5,290 identified records, 44 were included. Twenty-seven (61%) were RCTs and 17 (39%) were cohort studies. Thirteen studies (30%) reported data from Africa, 12 (27%) from Asia, 6 (14%) from South America, 5 (11%) from North America, and 4 (9%) from Europe. Four studies reported data from multiple continents. Summary estimates suggested smear conversion in 9% of patients at 2 weeks (95% CI 3%–24%, 1 single study [N = 1]), and 82% of patients at 2 months of treatment (95% CI 78%–86%, N = 10). Among baseline smear-positive patients, solid culture conversion occurred by 2 weeks in 5% (95% CI 0%–14%, N = 2), increasing to 88% at 2 months (95% CI 84%–92%, N = 20). At equivalent time points, liquid culture conversion was achieved in 3% (95% CI 1%–16%, N = 1) and 59% (95% CI 47%–70%, N = 8). Significant heterogeneity was observed. Further interrogation of the data to explain this heterogeneity was limited by the lack of disaggregation of results, including by factors such as HIV status, baseline smear status, and the presence or absence of lung cavitation. Conclusions This systematic review found that most patients remained culture positive at 2 weeks of TB treatment, challenging the view that individuals are not infectious after this interval. Culture positivity is, however, only 1 component of infectiousness, with reduced cough frequency and aerosol generation after TB treatment initiation likely to also be important. Studies that integrate our findings with data on cough dynamics could provide a more complete perspective on potential transmission of Mycobacterium tuberculosis by individuals on treatment. Trial registration Systematic review registration: PROSPERO 85226.

Effects of Aging on the Color and Translucency of Monolithic Translucent Y-TZP Ceramics: A Systematic Review and Meta-Analysis of In Vitro Studies

BioMed Research International ◽

10.1155/2021/8875023 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Chang-yuan Zhang ◽

Check Agingu ◽

James Kit Hon Tsoi ◽

Hao Yu

Keyword(s):

Systematic Review ◽

Meta Analysis ◽

Tetragonal Zirconia ◽

In Vitro Studies ◽

Cochrane Library ◽

Hydrothermal Aging ◽

Significant Difference ◽

Effects Of Aging ◽

Background. Monolithic restorations made of translucent yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) have become popular over the past few decades. However, whether aging affects the color and translucency of monolithic translucent Y-TZP is unclear. Objective. The aim of this systematic review and meta-analysis of in vitro studies was to evaluate the effects of aging on the color and translucency of monolithic translucent Y-TZP ceramics. Materials and Methods. This systematic review/meta-analysis was reported according to the PRISMA statement and registered in the OSF registries (https://osf.io/5qjmu). Four databases including Medline via the PubMed, Embase, and Web of Science databases and the Cochrane Library were searched using no publication year and language limits. The last search was executed on November 20, 2020. In vitro studies comparing the translucency and/or color of monolithic translucent Y-TZP ceramics before and after simulated aging were selected. Meta-analyses were performed using Review Manager software (version 5.3, Cochrane Collaboration, Oxford, UK) with random-effects models at a significance level of 0.05. A risk-of-bias assessment was also performed for the included studies. Results. Of the 188 potentially relevant studies, 13 were included in the systematic review. The hydrothermal aging duration ranged from 1 to 100 h at relatively similar temperatures (~134°C). In the general meta-analyses, the aged Y-TZP ceramics exhibited similar translucency parameter (TP), L ∗ , and b ∗ values compared with the nonaged controls ( P = .73 , P = .49 , and P = .62 , respectively). Moreover, there was a significant difference between the aged and nonaged Y-TZP ceramics in the a ∗ value ( P = .03 ; MD = − 0.26 ; 95% CI = − 0.51 to − 0.02 ), favoring the nonaged Y-TZP ceramics. The subgroup analyses showed that the duration of aging contributed to changes in the translucency and color of the Y-TZP ceramics. Conclusions. The optical properties of monolithic translucent Y-TZP ceramics were stable after hydrothermal aging at 134°C and 0.2 MPa for ≤20 h. Moreover, clinically unacceptable changes in the translucency and color of monolithic translucent Y-TZP ceramics were found after hydrothermal aging for >20 h.

Diagnostic accuracy of the Xpert MTB/RIF assay for tuberculous pericarditis: A systematic review and meta-analysis

PLoS ONE ◽

10.1371/journal.pone.0257220 ◽

2021 ◽

Vol 16 (9) ◽

pp. e0257220

Author(s):

Guocan Yu ◽

Fangming Zhong ◽

Yanqin Shen ◽

Hong Zheng

Keyword(s):

Gold Standard ◽

Meta Analysis ◽

Area Under The Curve ◽

Diagnostic Efficacy ◽

Tuberculous Pericarditis ◽

Meta Analyses ◽

Sensitivity Specificity ◽

Study Inclusion ◽

Composite Reference Standard

Objective The purpose of this study was to evaluate the diagnostic efficacy of Xpert MTB/RIF for tuberculous pericarditis (TBP). Methods We searched relevant databases for Xpert MTB/RIF for TBP diagnosis until April 2021 and screened eligible studies for study inclusion. We evaluated the effectiveness of Xpert MTB/RIF when the composite reference standard (CRS) and mycobacterial culture were the gold standards, respectively. We performed meta-analyses using a bivariate random-effects model, and when the heterogeneity was obvious, the source of heterogeneity was further discussed. Results We included seven independent studies comparing Xpert MTB/RIF with the CRS and six studies comparing it with culture. The pooled sensitivity, specificity, and area under the curve of Xpert MTB/RIF were 65% (95% confidence interval, 59–72%), 99% (97–100%), and 0.99 (0.97–0.99) as compared with the CRS, respectively, and 75% (53–88%), 99% (90–100%), and 0.94 (0.92–0.96) as compared with culture, respectively. There was no significant heterogeneity between studies when CRS was the gold standard, whereas heterogeneity was evident when culture was the gold standard. Conclusions The sensitivity of Xpert MTB/RIF for diagnosing TBP was moderate and the specificity was good; thus, Xpert MTB/RIF can be used in the initial diagnosis of TBP.

Association between Metabolites and the Risk of Lung Cancer: A Systematic Literature Review and Meta-Analysis of Observational Studies

Metabolites ◽

10.3390/metabo10090362 ◽

2020 ◽

Vol 10 (9) ◽

pp. 362 ◽

Cited By ~ 1

Author(s):

Kian Boon Lee ◽

Lina Ang ◽

Wai-Ping Yau ◽

Wei Jie Seow

Keyword(s):

Lung Cancer ◽

Cancer Risk ◽

Literature Review ◽

Systematic Literature Review ◽

Observational Studies ◽

Lung Cancer Risk ◽

Meta Analysis ◽

Cancer Type ◽

Globally, lung cancer is the most prevalent cancer type. However, screening and early detection is challenging. Previous studies have identified metabolites as promising lung cancer biomarkers. This systematic literature review and meta-analysis aimed to identify metabolites associated with lung cancer risk in observational studies. The literature search was performed in PubMed and EMBASE databases, up to 31 December 2019, for observational studies on the association between metabolites and lung cancer risk. Heterogeneity was assessed using the I2 statistic and Cochran’s Q test. Meta-analyses were performed using either a fixed-effects or random-effects model, depending on study heterogeneity. Fifty-three studies with 297 metabolites were included. Most identified metabolites (252 metabolites) were reported in individual studies. Meta-analyses were conducted on 45 metabolites. Five metabolites (cotinine, creatinine riboside, N-acetylneuraminic acid, proline and r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene) and five metabolite groups (total 3-hydroxycotinine, total cotinine, total nicotine, total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (sum of concentrations of the metabolite and its glucuronides), and total nicotine equivalent (sum of total 3-hydroxycotinine, total cotinine and total nicotine)) were associated with higher lung cancer risk, while three others (folate, methionine and tryptophan) were associated with lower lung cancer risk. Significant heterogeneity was detected across most studies. These significant metabolites should be further evaluated as potential biomarkers for lung cancer.