Meta-analysis in epidemiology, with special reference to studies of the association between exposure to environmental tobacco smoke and lung cancer: a critique

Systematic review with meta-analysis of the epidemiological evidence relating smoking to COPD, chronic bronchitis and emphysema

BACKGROUND

Smoking is a known cause of the outcomes COPD, chronic bronchitis (CB) and emphysema, but no previous systematic review exists. We summarize evidence for various smoking indices.

METHODS

Based on MEDLINE searches and other sources we obtained papers published to 2006 describing epidemiological studies relating incidence or prevalence of these outcomes to smoking. Studies in children or adolescents, or in populations at high respiratory disease risk or with co-existing diseases were excluded. Study-specific data were extracted on design, exposures and outcomes considered, and confounder adjustment. For each outcome RRs/ORs and 95% CIs were extracted for ever, current and ex smoking and various dose response indices, and meta-analyses and meta-regressions conducted to determine how relationships were modified by various study and RR characteristics.

RESULTS

Of 218 studies identified, 133 provide data for COPD, 101 for CB and 28 for emphysema. RR estimates are markedly heterogeneous. Based on random-effects meta-analyses of most-adjusted RR/ORs, estimates are elevated for ever smoking (COPD 2.89, CI 2.63-3.17, n = 129 RRs; CB 2.69, 2.50-2.90, n = 114; emphysema 4.51, 3.38-6.02, n = 28), current smoking (COPD 3.51, 3.08-3.99; CB 3.41, 3.13-3.72; emphysema 4.87, 2.83-8.41) and ex smoking (COPD 2.35, 2.11-2.63; CB 1.63, 1.50-1.78; emphysema 3.52, 2.51-4.94). For COPD, RRs are higher for males, for studies conducted in North America, for cigarette smoking rather than any product smoking, and where the unexposed base is never smoking any product, and are markedly lower when asthma is included in the COPD definition. Variations by sex, continent, smoking product and unexposed group are in the same direction for CB, but less clearly demonstrated. For all outcomes RRs are higher when based on mortality, and for COPD are markedly lower when based on lung function. For all outcomes, risk increases with amount smoked and pack-years. Limited data show risk decreases with increasing starting age for COPD and CB and with increasing quitting duration for COPD. No clear relationship is seen with duration of smoking.

CONCLUSIONS

The results confirm and quantify the causal relationships with smoking.

Vitamin analogues in chemoprevention of hepatocellular carcinoma after resection or ablation--a systematic review and meta-analysis

OBJECTIVE

While hepatic resection or local ablative therapy may provide a potentially curative treatment for hepatocellular carcinoma (HCC), more than half of these patients develop recurrent HCC within 5 years after treatment. Thus identification of any therapy which can decrease or delay the incidence of recurrence will improve the results of treatment. However, no chemopreventive agent has been approved for HCC.

METHODS

A MEDLINE database, Embase, Cancerlit (National Cancer Institute), and CBM (Chinese Biomedical Database) search from 1990 to 2009 was performed to identify relevant articles using the keywords "hepatocellular carcinoma," "vitamin analogue," and "chemoprevention." Additional papers were identified by a manual search of the references from the key articles. The fixed effect model was used for a meta-analysis.

RESULTS

Oral administration of acyclic retinoids (vitamin A analogue), and menatetrenone (vitamin K2 analogue) have been tested as chemopreventive agents after hepatic resection or local ablative therapy for HCC. There were one and four randomised, controlled trials (RCTs) which evaluated the efficacy of polyprenoic acid and menatetrenone, respectively. All studies were conducted in Japan. One RCT showed the preventive effect of polyprenoic acid in lowering the incidence of HCC recurrence after hepatic resection or percutaneous ethanol injection, and this effect lasted up to 199 weeks after randomization (or 151 weeks after completion of retinoid administration). Four RCTs evaluated the preventive efficacy of menatetrenone on HCC recurrence after hepatic resection or local ablative therapy. The results of three studies, as well as the meta-analysis of all four studies, showed significantly better tumour recurrence-free survival. The beneficial effect on the overall survival was less definite.

CONCLUSION

There is evidence to suggest that chemopreventive therapy after partial hepatectomy or local ablative therapy is beneficial in prolonging disease-free survival, but the evidence is less for an effect on the overall survival. To confirm the beneficial role of vitamin A or K analogues in the chemoprevention of HCC further and larger randomised trials are now required.

Systematic review of the epidemiological evidence comparing lung cancer risk in smokers of mentholated and unmentholated cigarettes

BACKGROUND

US mentholated cigarette sales have increased considerably over 50 years. Preference for mentholated cigarettes is markedly higher in Black people. While menthol itself is not genotoxic or carcinogenic, its acute respiratory effects might affect inhalation of cigarette smoke. This possibility seems consistent with the higher lung cancer risk in Black men, despite Black people smoking less and starting smoking later than White people. Despite experimental data suggesting similar carcinogenicity of mentholated and non-mentholated cigarettes, the lack of convincing evidence that mentholation increases puffing, inhalation or smoke uptake, and the similarity of lung cancer rates in Black and White females, a review of cigarette mentholation and lung cancer is timely given current regulatory interest in the topic.

METHODS

Epidemiological studies comparing lung cancer risk in mentholated and non-mentholated cigarette smokers were identified from MedLine and other sources. Study details were extracted and strengths and weaknesses assessed. Relative risk estimates were extracted, or derived, for ever mentholated use and for long-term use, overall and by gender, race, and current/ever smoking, and meta-analyses conducted.

RESULTS

Eight generally good quality studies were identified, with valid cases and controls, and appropriate adjustment for age, gender, race and smoking. The studies afforded good power to detect possible effects. However, only one study presented results by histological type, none adjusted for occupation or diet, and some provided no results by length of mentholated cigarette use.The data do not suggest any effect of mentholation on lung cancer risk. Adjusted relative risk estimates for ever use vary from 0.81 to 1.12, giving a combined estimate of 0.93 (95% confidence interval 0.84-1.02, n = 8), with no increase in males (1.01, 0.84-1.22, n = 5), females (0.80, 0.67-0.95, n = 5), White people (0.87, 0.75-1.03, n = 4) or Black people (0.90, 0.73-1.10, n = 4). Estimates for current and ever smokers are similar. The combined estimate for long-term use (0.95, 0.80-1.13, n = 4) again suggests no effect of mentholation.

CONCLUSION

Higher lung cancer rates in Black males cannot be due to their greater preference for mentholated cigarettes. While some study weaknesses exist, the epidemiological evidence is consistent with mentholation having no effect on the lung carcinogenicity of cigarettes.

The combined influence of oral contraceptives and human papillomavirus virus on cutaneous squamous cell carcinoma

The vast majority of cutaneous squamous cell carcinoma (CSCC) will occur in those with fair complexion, tendency to burn, and high ultraviolet radiation (UVR) exposure. Organ transplant recipients also are an important population at great risk for CSCC. An association has been reported between oral contraceptive (OC) use, human papillomavirus virus (HPV) and cervical cancer, and there could be a similar association for CSCC. The cutaneous HPV β-E6 protein, a close cousin of the transformative E6 protein underlying anogenital cancers, has been shown to inhibit apoptosis in response to UVR damage and stimulate morphologic transformation in rodent fibroblast cell lines. Furthermore, OC use has been shown to enhance HPV transcription and may contribute to CSCC risk through this pathway.

Summary of the epidemiological evidence relating snus to health

Interest in snus (Swedish-type moist snuff) as a smoking alternative has increased. This wide-ranging review summarizes evidence relating snus to health and to initiation and cessation of smoking. Meta-analyses are included. After smoking adjustment, snus is unassociated with cancer of the oropharynx (meta-analysis RR 0.97, 95% CI 0.68-1.37), oesophagus (1.10, 0.92-1.33), stomach (0.98, 0.82-1.17), pancreas (1.20, 0.66-2.20), lung (0.71, 0.66-0.76) or other sites, or with heart disease (1.01, 0.91-1.12) or stroke (1.05, 0.95-1.15). No clear associations are evident in never smokers, any possible risk from snus being much less than from smoking. "Snuff-dipper's lesion" does not predict oral cancer. Snus users have increased weight, but diabetes and chronic hypertension seem unaffected. Notwithstanding unconfirmed reports of associations with reduced birthweight, and some other conditions, the evidence provides scant support for any major adverse health effect of snus. Although some claims that snus reduces initiation or encourages quitting are unsoundly based, snus seems not to increase initiation, as indicated by few smokers using snus before starting and current snus use being unassociated with smoking in adults (the association in children probably being due to uncontrolled confounding), and there are no reports that snus discourages quitting.

Gene-wide association study between the methylenetetrahydrofolate reductase gene (MTHFR) and schizophrenia in the Japanese population, with an updated meta-analysis on currently available data

Methylenetetrahydrofolate reductase (MTHFR) is a critical molecule for single-carbon transfer reactions. Recent evidence suggests that polymorphisms of MTHFR are related to neural tube deficits and the pathogenesis of schizophrenia. While several studies have demonstrated associations between the gene encoding the MTHFR (MTHFR) polymorphisms and schizophrenia, these studies lack consistency. Therefore, we conducted a gene-wide association study (patients with schizophrenia = 696, control subjects = 747) and performed imputation analysis. Additionally, we performed meta-analysis on currently available data from 18 studies for two common functional polymorphisms (rs1801131 and rs1801133). There were no significant associations with schizophrenia in the single marker analysis for the seven tagging SNPs of MTHFR. In the haplotypic analysis, a nominally significant association was observed between the haplotypes, which included four SNPs (rs1801133, rs17421511, rs17037396, and rs9651118) and the schizophrenic patients. Additionally, the imputation analysis demonstrated there were several associated markers on the MTHFR chromosomal region. However, confirmatory analyses of three tagging SNPs (rs1801133, rs17037396, and rs9651118) and the top SNP (rs17421511) for the imputation results (patients with schizophrenia = 797, control subjects = 1025) failed to replicate the haplotypic analysis and the imputation results. These findings suggest that MTHFR polymorphisms are unlikely to be related to the development of schizophrenia in the Japanese population. However, since our meta-analysis results demonstrated strong support for association of rs1801133 with schizophrenia, further replication studies based on a gene-wide approach need to be considered.

Type 2 diabetes mellitus as a risk factor for the onset of depression: a systematic review and meta-analysis

AIMS/HYPOTHESIS

An earlier meta-analysis showed that diabetes is a risk factor for the development and/or recurrence of depression. Yet whether this risk is different for studies using questionnaires than for those relying on diagnostic criteria for depression has not been examined. This study examined the association of diabetes and the onset of depression by reviewing the literature and conducting a meta-analysis of longitudinal studies on this topic.

METHODS

EMBASE, MEDLINE and PsycInfo were searched for articles published up to September 2009. All studies that examined the relationship between type 2 diabetes and the onset of depression were included. Pooled relative risks were calculated using fixed and random effects models.

RESULTS

Eleven studies met our inclusion criteria for this meta-analysis. Based on the pooled data, including 48,808 cases of type 2 diabetes without depression at baseline, the pooled relative risk was 1.24 (95% CI 1.09-1.40) for the random effects model. This risk was significantly higher for studies relying on diagnostic criteria of depression than for studies using questionnaires. However, this difference was no longer significant when controlled for year of publication.

CONCLUSIONS/INTERPRETATION

Compared with non-diabetic controls, people with type 2 diabetes have a 24% increased risk of developing depression. The mechanisms underlying this relationship are still unclear and warrant further research.

A meta-analytic review of the psychosocial adjustment of youth with inflammatory bowel disease

OBJECTIVE

To conduct a meta-analytic review of psychosocial adjustment of youth with inflammatory bowel disease (IBD).

METHODS

Nineteen studies with a total of 1167 youth with IBD (M age = 14.33, 50% female) were included. Effect size (ES) estimates were calculated for anxiety symptoms & disorders, depressive symptoms & disorders, internalizing symptoms & disorders, externalizing symptoms, quality of life (QOL), social functioning, and self-esteem. Separate ESs were calculated for comparisons between IBD and youth with chronic illnesses versus healthy youth.

RESULTS

Youth with IBD had higher rates of depressive disorders and internalizing disorders than youth with other chronic conditions. Youth with IBD had higher parent-reported internalizing symptoms, lower parent- and youth-reported QOL, and lower youth-reported social functioning compared to healthy youth.

CONCLUSIONS

Clinical attention to depressive disorders, QOL, and social functioning may be particularly salient in the context of pediatric IBD.

The relation between smokeless tobacco and cancer in Northern Europe and North America. A commentary on differences between the conclusions reached by two recent reviews

BACKGROUND

Smokeless tobacco is an alternative for smokers who want to quit but require nicotine. Reliable evidence on its effects is needed. Boffetta et al. and ourselves recently reviewed the evidence on cancer, based on Scandinavian and US studies. Boffetta et al. claimed a significant 60-80% increase for oropharyngeal, oesophageal and pancreatic cancer, and a non-significant 20% increase for lung cancer, data for other cancers being "too sparse". We found increases less than 15% for oesophageal, pancreatic and lung cancer, and a significant 36% increase for oropharyngeal cancer, which disappeared in recent studies. We found no association with stomach, bladder and all cancers combined, using data as extensive as that for oesophageal, pancreatic and lung cancer. We explain these differences.

METHODS

For those cancers Boffetta et al. considered, we compared the methods, studies and risk estimates used in the two reviews.

RESULTS

One major reason for the difference is our more consistent approach in choosing between study-specific never smoker and combined smoker/non-smoker estimates. Another is our use of derived as well as published estimates. We included more studies, and avoided estimates for data subsets. Boffetta et al. also included some clearly biased or not smoking-adjusted estimates. For pancreatic cancer, their review included significantly increased never smoker estimates in one study and combined smoker/non-smoker estimates in another, omitting a combined estimate in the first study and a never smoker estimate in the second showing no increase. For oesophageal cancer, never smoker results from one study showing a marked increase for squamous cell carcinoma were included, but corresponding results for adenocarcinoma and combined smoker/non-smoker results for both cell types showing no increase were excluded. For oropharyngeal cancer, Boffetta et al. included a markedly elevated estimate that was not smoking-adjusted, and overlooked the lack of association in recent studies.

CONCLUSION

When conducting meta-analyses, all relevant data should be used, with clear rules governing the choice between alternative estimates. A systematic meta-analysis using pre-defined procedures and all relevant data gives a lower estimate of cancer risk from smokeless tobacco (probably 1-2% of that from smoking) than does the previous review by Boffetta et al.

Systematic review of the relation between smokeless tobacco and cancer in Europe and North America

BACKGROUND

Interest is rising in smokeless tobacco as a safer alternative to smoking, but published reviews on smokeless tobacco and cancer are limited. We review North American and European studies and compare effects of smokeless tobacco and smoking.

METHODS

We obtained papers from MEDLINE searches, published reviews and secondary references describing epidemiological cohort and case-control studies relating any form of cancer to smokeless tobacco use. For each study, details were abstracted on design, smokeless tobacco exposure, cancers studied, analysis methods and adjustment for smoking and other factors. For each cancer, relative risks or odds ratios with 95% confidence intervals were tabulated. Overall, and also for USA and Scandinavia separately, meta-analyses were conducted using all available estimates, smoking-adjusted estimates, or estimates for never smokers. For seven cancers, smoking-attributable deaths in US men in 2005 were compared with deaths attributable to introducing smokeless tobacco into a population of never-smoking men.

RESULTS

Eighty-nine studies were identified; 62 US and 18 Scandinavian. Forty-six (52%) controlled for smoking. Random-effects meta-analysis estimates for most sites showed little association. Smoking-adjusted estimates were only significant for oropharyngeal cancer (1.36, CI 1.04-1.77, n = 19) and prostate cancer (1.29, 1.07-1.55, n = 4). The oropharyngeal association disappeared for estimates published since 1990 (1.00, 0.83-1.20, n = 14), for Scandinavia (0.97, 0.68-1.37, n = 7), and for alcohol-adjusted estimates (1.07, 0.84-1.37, n = 10). Any effect of current US products or Scandinavian snuff seems very limited. The prostate cancer data are inadequate for a clear conclusion.Some meta-analyses suggest a possible effect for oesophagus, pancreas, larynx and kidney cancer, but other cancers show no effect of smokeless tobacco. Any possible effects are not evident in Scandinavia. Of 142,205 smoking-related male US cancer deaths in 2005, 104,737 are smoking-attributable. Smokeless tobacco-attributable deaths would be 1,102 (1.1%) if as many used smokeless tobacco as had smoked, and 2,081 (2.0%) if everyone used smokeless tobacco.

CONCLUSION

An increased risk of oropharyngeal cancer is evident most clearly for past smokeless tobacco use in the USA, but not for Scandinavian snuff. Effects of smokeless tobacco use on other cancers are not clearly demonstrated. Risk from modern products is much less than for smoking.

Citrus fruit intake and pancreatic cancer risk: a quantitative systematic review

OBJECTIVES

The purpose of this systematic review was to investigate the association between dietary intake of citrus fruits and pancreatic cancer risk.

METHODS

Authors searched electronic databases and the reference lists of publications of studies addressing diet and pancreatic cancer up to December 2007. All of the epidemiological studies that obtained individual data on dietary intake of citrus fruits and presented risk estimates of the association between intake of citrus fruits and risk of pancreatic cancer were identified and included. Using general variance-based methods, study-specific odds ratios (ORs)/relative risk and associated confidence interval (CI)/SE for highest versus lowest intake of citrus fruits level were extracted from each article.

RESULTS

Nine articles including 4 case-control studies and 5 cohort studies proved eligible. Overall summary OR using random effect model suggested an inverse association in risk of pancreatic cancer with intake of citrus fruits (summary OR, 0.83; 95% CI, 0.70-0.98) with large heterogeneity across studies (I = 49.9%).

CONCLUSIONS

Pooled results from observational studies showed an inverse association between intake of citrus fruits and the risk of pancreatic cancer, although results vary substantially across studies, and the apparent effect is restricted to the weaker study design (case-control studies).

Intraoperative allogeneic red blood cell transfusion in ampullary cancer outcome after curative pancreatoduodenectomy: a clinical study and meta-analysis

BACKGROUND

Allogeneic blood transfusion (ABT) containing packed red blood cells (RBCs) has a known immunosuppressive effect that may affect cancer metastases and recurrence. This study examined whether intraoperative allogeneic RBC transfusion is an independent risk factor of adverse outcome in patients with ampullary carcinoma after curative pancreatoduodenectomy.

METHODS

The clinical data of 67 patients with carcinoma of the ampulla of Vatar underwent pancreatoduodenectomy between 1999 and 2004 were analyzed, and long-term follow-up visits were made for all patients. Kaplan-Meier statistics and Cox proportional hazard methodology were used to perform univariate and multivariate analysis to identify independent risk factors for survival. For the meta-analysis, all English-language studies regarding blood transfusion from carcinoma of the ampulla of Vatar or ampullary carcinoma and prognostic factors or factors for survival from 1995 to 2007 were reviewed, and contingency tables were constructed from which a summary relative risk was calculated.

RESULTS

There were 43 patients (64.2%) who received an intraoperative ABT. The amount of intraoperative ABT ranged from 2 to 13 (mean, 4.25) units; there were 18 patients transfused at 2 units, and 25 patients transfused > or =3 units. The follow-up ranged from 2 to 90 (mean, 49) months. Forty-five patients (67.2%) died as a result of tumor progression. For patients transfused > or =3 units, median and cumulative 3-year and 5-year survivals were poorer significantly than that of patients transfused with 2 units and/or nontransfused patients (P < 0.05). After multivariate analysis, except for presence of lymph node metastasis (P = 0.023) and pancreatic invasion (P = 0.024), the intraoperative ABT > or =3 units was found to be an independent poor prognostic factor for those with ampullary cancer after curative pancreatoduodenectomy either (relative risk, 2.082; 95% confidence interval (CI), 1.048-4.135; P = 0.036). Meta-analysis of 346 patients showed the summary relative risk of an adverse outcome after intraoperative ABT in these studies was 2.55 (95% CI, 1.59-4.1).

CONCLUSIONS

The amount of intraoperative ABT is one of the important factors that adversely influenced survival in patients with ampullary cancer after curative pancreatoduodenectomy. Healing anemia preoperatively and careful dissection to minimize intraoperative bleeding as much as possible are mandatory for reducing risk of the intraoperative ABT.

Systematic review of the relation between smokeless tobacco and cancer of the pancreas in Europe and North America

Background

Recent reviews claiming smokeless tobacco increases pancreatic cancer risk appear not to have considered all available epidemiological evidence; nor were meta-analyses included. We present a systematic review of studies from North America and Europe, since data are lacking from other continents. Risk is also difficult to quantify elsewhere due to the various products, compositions and usage practices involved.

Methods

Epidemiological studies were identified that related pancreatic cancer to use of snuff, chewing tobacco or unspecified smokeless tobacco. Study details and effect estimates (relative risks or odds ratios) were extracted, and combined by meta-analyses.

Results

Nine North American and two Scandinavian studies were identified. Reporting was limited in four studies, so only seven were included in meta-analyses, some providing results for never smokers, some for the overall population of smokers and non-smokers, and some for both.

Giving preference to study-specific estimates for the overall population, if available, and for never smokers otherwise, the random-effects estimate for ever smokeless tobacco use was 1.03 (95% confidence interval 0.71–1.49) based on heterogeneous estimates from seven studies. The estimate varied little by continent, study type, or type of smokeless tobacco.

Giving preference to estimates for never smokers, if available, and overall population estimates otherwise, the estimate was 1.14 (0.67–1.93), again based on heterogeneous estimates. Estimates varied (p = 0.014) between cohort studies (1.75, 1.20–2.54) and case-control studies (0.84, 0.36–1.97). The value for cohort studies derived mainly from one study, which reported an increase for never smokers (2.0, 1.2–3.3), but not overall (0.9, 0.7–1.2). This study also contributed to increases seen for snuff use and for European studies, significant only in fixed-effect analyses.

The studies have various weaknesses, including few exposed cases, reliance in cohort studies on exposure recorded at baseline, poor control groups in some case-control studies, and lack of a dose-response. Publication bias, with some negative studies not being presented, is also possible.

Conclusion

At most, the data suggest a possible effect of smokeless tobacco on pancreatic cancer risk. More evidence is needed. If any risk exists, it is highly likely to be less than that from smoking.

Selective reporting of adjusted estimates in observational epidemiology studies: reasons and implications for meta-analyses

For meta-analyses of observational epidemiology studies, unadjusted and adjusted study estimates are often extracted. However, there is evidence of selective reporting of adjusted study estimates. We investigate adjustment reporting bias, examining the reasons why some studies do not contribute an adjusted estimate to a meta-analysis. Ten published meta-analyses were re-analysed to assess evidence of adjustment reporting bias and over 100 primary studies were read to investigate why they did not contribute an adjusted estimate to a meta-analysis. Selective reporting of adjusted estimates may lead to a bias in some meta-analyses when adjusted study estimates are not reported because univariate analyses indicated a non-significant effect. We recommend that unadjusted and adjusted study estimates be extracted for a meta-analysis. If adjusted estimates cannot be obtained, the reasons for this should be investigated and sensitivity analyses could be used to assess the impact of this on the meta-analysis.

Meta-analysis of repeated measures study designs

RATIONALE, AIMS AND OBJECTIVES

Repeated measures studies are found in many areas of research, particularly in areas of healthcare. There is currently little information available to inform the method of meta-analysis of repeated measures studies so that the structural dependence of the data is appropriately accommodated and the findings are meaningful.

METHOD

Using a published meta-analysis on the impact of diet advice on weight reduction of obese or overweight individuals, we demonstrate possible approaches for repeated measures meta-analysis. These approaches differ in terms of the type of result obtained (e.g. effect at a particular time-point, trend over time, change between time-points) and the data needed for the analysis (e.g. means, regression slope estimates). Some approaches involve violating assumptions of independence in the data structure and so to investigate the impact of this violation a simulation study is carried out.

RESULTS

The different approaches described for the meta-analyses of repeated measures studies can all provide useful effect estimates depending on the question to be addressed by the meta-analysis. However, violation of the independence assumption in some approaches can lead to biased estimates.

CONCLUSIONS

In practice, the methods available to carry out meta-analyses of repeated measures studies will not only depend upon the question of interest, but also on the data available from the primary studies.

Antiviral therapy of hepatitis C in chronic kidney diseases: meta-analysis of controlled clinical trials

Hepatitis C virus (HCV) infection remains frequent in patients with chronic kidney disease and the detrimental role of HCV on survival is well-established in this population. Several authors have reported on efficacy and safety of antiviral therapy for hepatitis C in this polulation but there is no clear consensus on management. To evaluate efficacy and safety of antiviral therapy for hepatitis C in patients with chronic kidney disease, we performed a systematic review of the published medical literature and completed a meta-analysis of controlled clinical trials. The primary outcome was sustained virological response (as a measure of efficacy); the secondary outcome was drop-out rate (as a measure of tolerability). We used the random effects model of Der Simonian and Laird, with heterogeneity and sensitivity analyses. We identified 13 studies including 539 unique patients; 10 (76.9%) concerned patients on maintenance dialysis. Only prospective, controlled clinical trials were included. Pooling of study results showed a significant increase of viral response in study (patients treated with antiviral therapy) than control patients (patients who did not receive therapy), the pooled odds ratio (OR) of failure to obtain a sustained viral response was 0.081 [95% confidence intervals (CI), 0.029-0.230], P = 0.0001. The pooled OR of drop-out rate was significantly increased in study vs control patients, OR = 0.389 (95% CI, 0.155-0.957), P = 0.04. The studies were heterogeneous with regard to viral response and drop-out rate. In the subset of clinical trials (n = 6) involving only dialysis patients receiving interferon (IFN) monotherapy for chronic HCV, there was a significant difference in the risk of failure to obtain a sustained viral response (study vs control patients), OR = 0.054 (95% CI, 0.019; 0.150), P = 0.0001 (random-effects model). No significant (NS) heterogeneity was found (Q = 14.604, P = 1.0). No difference in the drop-out rate between study and control patients was shown, OR = 0.920 (95% CI, 0.367; 2.311), NS. This result being homogeneous (Q = 3.639, P = 0.388). Our meta-analysis showed that the viral response was greater in patients with chronic kidney disease who received antiviral therapy than controls. No difference in the drop-out rate between study and control patients occurred in the subgroup of dialysis patients on IFN monotherapy. These results support IFN-based therapy for hepatitis C in patients on maintenance dialysis.

Citrus fruit intake and stomach cancer risk: a quantitative systematic review

BACKGROUND

The purpose of this systematic review was to investigate the association between dietary intake of citrus fruits and gastric cancer risk.

METHODS

We searched electronic databases and the reference lists of publications on diet and stomach cancer studies until April 2007. All of the epidemiological studies that obtained individual data on dietary intake of citrus fruits and presented risk estimates of the association between intake of citrus fruits and risk of stomach cancer were identified and included in this review. Using general variance-based methods, study-specific odds ratio (OR)/ relative risk (RR) and associated confidence interval (CI)/ standard error (SE) for highest versus lowest intake of citrus fruits level were extracted from each article.

RESULTS

Fourteen articles, including six hospital-based case-control studies, six community-based case-control studies, and two cohort studies, proved eligible. Overall summary OR using a fixed-effect model showed a 28% reduction in risk of stomach cancer associated with high intake of citrus fruits (summary OR = 0.72; 95% CI = 0.64-0.81; P value <0.0001); results were consistent across studies (I(2) = 0, where I(2) describes the percentage of total variation across studies because of heterogeneity rather than chance). Also, visual inspection of the results did not suggest a publication bias.

CONCLUSION

Pooled results from observational studies support a protective effect of high citrus fruit intake in the risk of stomach cancer.

Systematic review of the relation between smokeless tobacco and non-neoplastic oral diseases in Europe and the United States

Background

How smokeless tobacco contributes to non-neoplastic oral diseases is unclear. It certainly increases risk of oral mucosal lesions, but reviewers disagree as to other conditions. In some areas, especially South-East Asia, risk is difficult to quantify due to the many products, compositions (including non-tobacco ingredients), and usage practices involved. This review considers studies from Europe (in practice mainly Scandinavia) and from the USA.

Methods

Experimental and epidemiological studies published in 1963–2007 were identified that related risk of oral lesions to smokeless tobacco use. Data were assessed separately for oral mucosal lesions, periodontal and gingival diseases, dental caries and tooth loss, and oral pain.

Results

Oral mucosal lesions: Thirty-three epidemiological studies consistently show a strong dose-related effect of current snuff on oral mucosal lesion prevalence. In Scandinavia, users have a near 100% prevalence of a characteristic "snuff-induced lesion", but prevalence of the varied lesions reported in the USA is lower. Associations with chewing tobacco are weaker. The lack of clear association with former use suggests reversibility following cessation, consistent with experimental studies showing rapid lesion regression on quitting.

Periodontal and gingival diseases: Two of four studies report a significant association of snuff with attachment loss and four out of eight with gingival recession. Snuff is not clearly related to gingivitis or periodontal diseases. Limited evidence suggests chewing tobacco is unrelated to periodontal or gingival diseases.

Tooth loss: Swedish studies show no association with snuff, but one US study reported an association with snuff, and another with chewing tobacco.

Dental caries: Evidence from nine studies suggests a possible relationship with use of smokeless tobacco, particularly chewing tobacco, and the risk of dental caries.

Oral pain: Limited evidence precludes any clear conclusion.

Conclusion

This review confirms the strong association of current use of smokeless tobacco, particularly snuff, with prevalence of oral mucosal lesions. It provides suggestive evidence of an association of snuff use with gingival recession and attachment loss, and of chewing tobacco with dental caries. While smokeless tobacco clearly increases risk of oral mucosal lesions, interpretation for other endpoints is limited by study weaknesses, including poor confounding control.

A quality-effects model for meta-analysis

We introduce a quality-effects approach that combines evidence from a series of trials comparing 2 interventions. This approach incorporates the heterogeneity of effects in the analysis of the overall interventional efficacy. However, unlike the random-effects model based on observed between-trial heterogeneity, we suggest adjustment based on measured methodological heterogeneity between studies. We propose a simple noniterative procedure for computing the combined effect size under this model and suggest that this could represent a more convincing alternative to the random effects model.

Facilitating meta-analyses by deriving relative effect and precision estimates for alternative comparisons from a set of estimates presented by exposure level or disease category

Epidemiological studies relating a particular exposure to a specified disease may present their results in a variety of ways. Often, results are presented as estimated odds ratios (or relative risks) and confidence intervals (CIs) for a number of categories of exposure, for example, by duration or level of exposure, compared with a single reference category, often the unexposed. For systematic literature review, and particularly meta-analysis, estimates for an alternative comparison of the categories, such as any exposure versus none, may be required. Obtaining these alternative comparisons is not straightforward, as the initial set of estimates is correlated. This paper describes a method for estimating these alternative comparisons based on the ideas originally put forward by Greenland and Longnecker, and provides implementations of the method, developed using Microsoft Excel and SAS. Examples of the method based on studies of smoking and cancer are given. The method also deals with results given by categories of disease (such as histological types of a cancer). The method allows the use of a more consistent comparison when summarizing published evidence, thus potentially improving the reliability of a meta-analysis.

Meta-analysis of the relation between European and American smokeless tobacco and oral cancer

BACKGROUND

Smokeless tobacco is often referred to as a major contributor to oral cancer. In some regions, especially Southeast Asia, the risk is difficult to quantify due to the variety of products, compositions (including non-tobacco ingredients) and usage practices involved. In Western populations, the evidence of an increased risk in smokeless tobacco users seems unclear, previous reviews having reached somewhat differing conclusions. We report a detailed quantitative review of the evidence in American and European smokeless tobacco users, and compare our findings with previous reviews and meta-analyses.

METHODS

Following literature review a meta-analysis was conducted of 32 epidemiological studies published between 1920 and 2005 including tests for homogeneity and publication bias.

RESULTS

Based on 38 heterogeneous study-specific estimates of the odds ratio or relative risk for smokeless tobacco use, the random-effects estimate was 1.87 (95% confidence interval 1.40-2.48). The increase was mainly evident in studies conducted before 1980. No increase was seen in studies in Scandinavia. Restricting attention to the seven estimates adjusted for smoking and alcohol eliminated both heterogeneity and excess risk (1.02; 0.82-1.28). Estimates also varied by sex (higher in females) and by study design (higher in case-control studies with hospital controls) but more clearly in studies where estimates were unadjusted, even for age. The pattern of estimates suggests some publication bias. Based on limited data specific to never smokers, the random-effects estimate was 1.94 (0.88-4.28), the eight individual estimates being heterogeneous and based on few exposed cases.

CONCLUSION

Smokeless tobacco, as used in America or Europe, carries at most a minor increased risk of oral cancer. However, elevated risks in specific populations or from specific products cannot definitely be excluded.

Circulatory disease and smokeless tobacco in Western populations: a review of the evidence

BACKGROUND

Use of oral snuff or 'snus' has risen in Sweden. Sales of snuff in the US have also risen, overtaking sales of chewing tobacco. There is some evidence that nicotine contributes to circulatory disease (CID) from smoking. We therefore reviewed the evidence relating smokeless tobacco (ST) to CID and related risk factors.

METHODS

Publications that described relevant cohort, case-control and cross-sectional studies were identified from in-house files, a Medline search in December 2005 and reference lists. Relative risks (RRs) and odds ratios (ORs) for ischaemic heart disease, stroke and all CID for ST use, stratified by smoking habit, were estimated and combined by meta-analysis to provide an overall RR estimate. For diabetes, increased blood pressure, and other risk factors, evidence was qualitatively reviewed, with results from clinical studies also considered.

RESULTS

ST use in non-smokers was associated with an increased risk of heart disease (RR 1.12, 95% CI 0.99-1.27, n = 8), stroke (1.42, 1.29-1.57, n = 5) and CID (1.25, 1.14-1.37, n = 3). The increases mainly derived from two large US studies. The Swedish studies provided little evidence of an increase for heart disease (1.06, 0.83-1.37, n = 5) or stroke (1.17, 0.80-1.70, n = 2), although the estimates by country are not notably heterogeneous, even for stroke (P = 0.29). No dose-response was evident. No increase was seen in former users of ST, or in ST users who also smoked. No clear relationship to diabetes was seen. In the US, an acute blood pressure rise following ST use was consistently reported, and isolated reports linked specific risk factors to ST. In Sweden, though one study reported that snuff acutely increased blood pressure, and two linked snuff to Raynaud-type symptoms, the overall evidence for an effect was inconclusive. Swedish studies generally showed no chronic effect of snuff on blood pressure or various risk factors.

CONCLUSIONS

Any CID risk from ST appears to be substantially less than from smoking, and no clear risk from Swedish snuff is seen. However, the overall evidence is limited.

Predicting nursing home admission in the U.S: a meta-analysis

BACKGROUND

While existing reviews have identified significant predictors of nursing home admission, this meta-analysis attempted to provide more integrated empirical findings to identify predictors. The present study aimed to generate pooled empirical associations for sociodemographic, functional, cognitive, service use, and informal support indicators that predict nursing home admission among older adults in the U.S.

METHODS

Studies published in English were retrieved by searching the MEDLINE, PSYCINFO, CINAHL, and Digital Dissertations databases using the keywords: "nursing home placement," "nursing home entry," "nursing home admission," and "predictors/institutionalization." Any reports including these key words were retrieved. Bibliographies of retrieved articles were also searched. Selected studies included sampling frames that were nationally- or regionally-representative of the U.S. older population.

RESULTS

Of 736 relevant reports identified, 77 reports across 12 data sources were included that used longitudinal designs and community-based samples. Information on number of nursing home admissions, length of follow-up, sample characteristics, analysis type, statistical adjustment, and potential risk factors were extracted with standardized protocols. Random effects models were used to separately pool the logistic and Cox regression model results from the individual data sources. Among the strongest predictors of nursing home admission were 3 or more activities of daily living dependencies (summary odds ratio [OR] = 3.25; 95% confidence interval [CI], 2.56-4.09), cognitive impairment (OR = 2.54; CI, 1.44-4.51), and prior nursing home use (OR = 3.47; CI, 1.89-6.37).

CONCLUSION

The pooled associations provided detailed empirical information as to which variables emerged as the strongest predictors of NH admission (e.g., 3 or more ADL dependencies, cognitive impairment, prior NH use). These results could be utilized as weights in the construction and validation of prognostic tools to estimate risk for NH entry over a multi-year period.

Predicting nursing home admission in the U.S: a meta-analysis

BACKGROUND

While existing reviews have identified significant predictors of nursing home admission, this meta-analysis attempted to provide more integrated empirical findings to identify predictors. The present study aimed to generate pooled empirical associations for sociodemographic, functional, cognitive, service use, and informal support indicators that predict nursing home admission among older adults in the U.S.

METHODS

Studies published in English were retrieved by searching the MEDLINE, PSYCINFO, CINAHL, and Digital Dissertations databases using the keywords: "nursing home placement," "nursing home entry," "nursing home admission," and "predictors/institutionalization." Any reports including these key words were retrieved. Bibliographies of retrieved articles were also searched. Selected studies included sampling frames that were nationally- or regionally-representative of the U.S. older population.

RESULTS

Of 736 relevant reports identified, 77 reports across 12 data sources were included that used longitudinal designs and community-based samples. Information on number of nursing home admissions, length of follow-up, sample characteristics, analysis type, statistical adjustment, and potential risk factors were extracted with standardized protocols. Random effects models were used to separately pool the logistic and Cox regression model results from the individual data sources. Among the strongest predictors of nursing home admission were 3 or more activities of daily living dependencies (summary odds ratio [OR] = 3.25; 95% confidence interval [CI], 2.56-4.09), cognitive impairment (OR = 2.54; CI, 1.44-4.51), and prior nursing home use (OR = 3.47; CI, 1.89-6.37).

CONCLUSION

The pooled associations provided detailed empirical information as to which variables emerged as the strongest predictors of NH admission (e.g., 3 or more ADL dependencies, cognitive impairment, prior NH use). These results could be utilized as weights in the construction and validation of prognostic tools to estimate risk for NH entry over a multi-year period.

Efficacy of folic acid supplementation in stroke prevention: a meta-analysis

BACKGROUND

The efficacy of treatments that lower homocysteine concentrations in reducing the risk of cardiovascular disease remains controversial. Our aim was to do a meta-analysis of relevant randomised trials to assess the efficacy of folic acid supplementation in the prevention of stroke.

METHODS

We collected data from eight randomised trials of folic acid that had stroke reported as one of the endpoints. Relative risk (RR) was used as a measure of the effect of folic acid supplementation on the risk of stroke with a random effect model. The analysis was further stratified by factors that could affect the treatment effects.

FINDINGS

Folic acid supplementation significantly reduced the risk of stroke by 18% (RR 0.82, 95% CI 0.68-1.00; p=0.045). In the stratified analyses, a greater beneficial effect was seen in those trials with a treatment duration of more than 36 months (0.71, 0.57-0.87; p=0.001), a decrease in the concentration of homocysteine of more than 20% (0.77, 0.63-0.94; p=0.012), no fortification or partly fortified grain (0.75, 0.62-0.91; p=0.003), and no history of stroke (0.75, 0.62-0.90; p=0.002). In the corresponding comparison groups, the estimated RRs were attenuated and insignificant.

INTERPRETATION

Our findings indicate that folic acid supplementation can effectively reduce the risk of stroke in primary prevention.

Blood Transfusion and Risk of Metastatic Disease or Recurrence in Patients Undergoing Immediate TRAM Flap Breast Reconstruction: A Clinical Study and Meta-Analysis

BACKGROUND

The transfusion of blood products has a known immunomodulatory effect that may affect cancer recurrence. The present study examined whether blood transfusion is an independent risk factor for recurrence or development of metastatic disease among patients undergoing immediate breast reconstruction with a transverse rectus abdominis musculocutaneous (TRAM) flap.

METHODS

Records of 103 patients who underwent mastectomy and immediate reconstruction with a TRAM flap between 1991 and 2001 were reviewed. A logistic regression analysis was used to identify independent risk factors for metastasis or recurrence. For the meta-analysis, all English-language studies regarding blood transfusion and breast cancer recurrence were reviewed, and 2 x 2 contingency tables were constructed from which a summary relative risk was calculated.

RESULTS

There were 57 free and 35 pedicle TRAM flaps. Forty-nine patients (48 percent) received perioperative transfusion of nonautologous blood. Twenty patients (19 percent) experienced metastatic disease or local recurrence. Follow-up ranged from 4 to 14 years (mean, 6.7 years). There was a higher observed rate of adverse outcome in patients who received transfusion, but this was not statistically significant (p = 0.90). Of the 11 articles identified by the meta-analysis, eight used a regression analysis controlling for the effect of stage and nodal status. The summary relative risk in these studies was 1.03 (95% CI, 0.90 to 1.26).

CONCLUSIONS

Perioperative blood transfusion does not seem to be an independent risk factor for metastasis or cancer recurrence in patients undergoing TRAM flap reconstruction. The observed correlation in this and prior studies may be due to the effect of other, more significant factors, such as tumor stage and nodal status.

Environmental tobacco smoke exposure and risk of breast cancer in nonsmoking women: a review with meta-analyses

Recent authoritative reviews consider smoking has no effect on breast cancer risk, but some studies report an increase from environmental tobacco smoke (ETS). We reviewed the overall evidence on ETS and breast cancer in nonsmoking women. We extracted details of available studies, derived relative risk (RR) estimates with confidence intervals (CIs) for various ETS exposure indices and conducted meta-analyses. Using an index for each study most closely equivalent to "spouse ever smoked," a weak, but significant, association was seen (random-effects RR = 1.12, 95% CI = 1.02-1.24, n = 22). However, the estimates were heterogeneous: close to 1.0 for prospective, North American and larger studies, and those adjusting for many potential confounders, but significantly (p < .05) elevated in case-control, European, and smaller studies, and those accounting for fewer potential confounders. Risk was increased in premenopausal women (RR = 1.54, 95% CI = 1.16-2.05, n = 10), but not postmenopausal women. Dose-response findings were similarly heterogeneous. No significant increase was seen for ETS in childhood or the workplace or from the spouse specifically, but an increase was seen for total exposure (RR = 1.54, 95% CI = 1.17-2.04, n = 6). Increases mainly derive from case-control studies asking detailed ETS histories, where RRs depend heavily on who is classified in the totally unexposed reference group, and may be prone to recall bias. Results from prospective studies using similar histories are needed. Study weaknesses and possible publication bias also limit interpretation. Because of the inherent implausibility that ETS exposure might cause breast cancer, given the similar risks of smokers and nonsmokers, one cannot confidently conclude ETS exposure increases risk in nonsmokers.

Predicting coma and other low responsive patients outcome using event-related brain potentials: a meta-analysis

OBJECTIVE

A meta-analysis was performed to estimate the predictive power (odd ratio, OR) for awakening of auditory event-related potential (ERP) components in low responsive patients with stroke or hemorrhage, trauma, anoxic, post-operative, and metabolic encephalopathy etiologies.

METHODS

We reviewed MEDLINE and analyzed citations for retrieved articles. Logistic regressions were applied on patient samples (Glasgow Coma Scale <12) across and for separate etiologies.

RESULTS

For stroke and hemorrhage the ORs with 95% confidence intervals were: 2.05 [1.12-3.75] (N100), 4.47 [1.92-10.44] (MMN), 10.29 [2.00-52.79] (P300), for trauma: 1.63 [0.70-3.80] (N100), 4.72 [1.35-16.44] (MMN), 12.89 [4.82-34.43] (P300), anoxic: 8.03 [2.83-22.75] (N100), 15.50 [4.27-56.26] (MMN), 5.93 [2.38-14.77] (P300), post-operative: 10.66 [1.98-57.50] (N100), metabolic encephalopathy: 2.12 [0.34-13.13] (N100), 3.60 [0.28-46.36] (MMN), 7.71 [0.75-79.77] (P300), and all etiologies: 2.85 [1.91-4.27] (N100), 6.53 [3.55-12.01] (MMN), and 8.79 [4.88-15.83] (P300). Based on six N100 studies (N=548 patients), five MMN studies (N=470), and six P300 studies (N=313), the N100, MMN, or P300, when present, significantly predicted awakening, P300 and MMN being significantly better predictors than N100.

CONCLUSIONS

The MMN and P300 appear to be reliable predictors of awakening.

SIGNIFICANCE

The prognostic assessment of low responsive patients with auditory ERP should take into account both MMN and P300.

Verbal fluency in HIV infection: a meta-analytic review

Given the largely prefrontostriatal neuropathogenesis of HIV-associated neurobehavioral deficits, it is often presumed that HIV infection leads to greater impairment on letter versus category fluency. A meta-analysis of the HIV verbal fluency literature was conducted (k = 37, n = 7110) to assess this hypothesis and revealed generally small effect sizes for both letter and category fluency, which increased in magnitude with advancing HIV disease severity. Across all studies, the mean effect size of category fluency was slightly larger than that of letter fluency. However, the discrepancy between category and letter fluency dissipated in a more conservative analysis of only those studies that included both tests. Thus, HIV-associated impairments in letter and category fluency are of similar magnitude, suggesting that mild word generation deficits are evident in HIV, regardless of whether traditional letter or semantic cues are used to guide the word search and retrieval process.

The expectation effect and cardiac pacing for refractory vasovagal syncope

BACKGROUND

Clinical trials of pacing for vasovagal syncope have shown conflicting results. We performed a meta-analysis to determine whether permanent pacemaker therapy prevents refractory vasovagal syncope.

METHODS

Randomized trials comparing pacemaker therapy with medical therapy, usual care, placebo, or different pacing algorithms in the prevention of recurrent vasovagal syncope were considered. The primary endpoint was first recurrence of syncope.

RESULTS

Nine randomized trials (2 double blind, 7 open label or single blind) were included. There was significant heterogeneity when all 9 trials were pooled (P=.0009 and I(2)=69.6%), reflecting methodological diversity in blinding and the nature of the control therapy. When pooled by trial methodology, heterogeneity was no longer apparent. Permanent pacing reduced the risk of recurrent syncope in unblinded studies (odds ratio [OR] 0.09, 95% confidence interval [CI], 0.04 to 0.22) and in studies comparing pacemaker algorithms (OR 0.04, 95% CI, 0.0 to 0.23). No effect was seen in double-blinded trials (OR 0.83, 95% CI, 0.41 to 1.70). Awareness that a permanent pacemaker was implanted and functional was associated with a significant 'expectation' effect, which itself reduced the risk of recurrent syncope (OR 0.16, 95% CI, 0.06 to 0.40, P=.0001). Results were similar when restricted to patients with a marked cardioinhibitory response on baseline tilt table testing.

CONCLUSION

The results of small, preliminary trials have overestimated the treatment effect of pacemakers due to a lack of blinding of physicians and patients. Blinded trials suggest that the apparent response is due to a strong expectation response to pacing.

Challenging the epidemiologic evidence on passive smoking: tactics of tobacco industry expert witnesses

OBJECTIVE

To analyse the statements given by tobacco industry defence witnesses during trial testimonies and depositions in second-hand smoke cases and in parallel, to review criticisms of epidemiology in industry-funded publications in order to identify strategies for discrediting epidemiologic evidence on passive smoking health effects.

METHODS

A collection of depositions and trial testimony transcripts from tobacco industry-related lawsuits filed in the United States during the 1990s, was compiled and indexed by the Tobacco Deposition and Trial Testimony Archive (DATTA). Statements in DATTA made by expert witnesses representing the tobacco industry relating to the health effects of passive smoking were identified and reviewed. Industry-supported publications within the peer-reviewed literature were also examined for statements on exposure misclassification, meta-analysis, and confounding.

RESULTS

The witnesses challenged causation of adverse health effects of passive smoking by citing limitations of epidemiologic research, raising methodological and statistical issues, and disputing biological plausibility. Though not often cited directly by the witnesses, the defence tactics mirrored the strategies used in industry-funded reports in the peer-reviewed literature.

CONCLUSION

The tobacco industry attempted to redirect the focus and dialogue related to the epidemiologic evidence on passive smoking. This approach, used by industry experts in trial testimony and depositions, placed bias as a certain alternative to causation of diseases related to passive smoking and proposed an unachievable standard for establishing the mechanism of disease.

Postsurgical infections are reduced with specialized nutrition support

OBJECTIVE

The objective was to examine the relationship between pre-, peri-, and postoperative specialized nutritional support with immune-modulating nutrients and postoperative morbidity in patients undergoing elective surgery.

METHODS

Studies were identified by searching MEDLINE, review article bibliographies, and abstracts and proceedings of scientific meetings. All randomized clinical trials in which patients were supplemented by the IMPACT formula before and/or after elective surgery and the clinical outcomes reported were included in the meta-analysis. Seventeen studies (n=2,305), 14 published (n=2,102), and 3 unpublished (n=203), fulfilled the inclusion criteria. Ten studies (n=1,392) examined the efficacy of pre- or perioperative IMPACT supplementation in patients undergoing elective surgery, whereas 7 (n=913) assessed postoperative efficacy. Fourteen of the studies (n=2,083) involved gastrointestinal (GI) surgical patients. Postoperative complications, mortality, and length of stay in hospital (LOS) were major outcomes of interest.

RESULTS

IMPACT supplementation, in general, was associated with significant (39%-61%) reductions in postoperative infectious complications and a significant decrease in LOS in hospital by an average of 2 days. The greatest improvement in postoperative outcomes was observed in patients receiving specialized nutrition support as part of their preoperative treatment. In GI surgical patients, anastomotic leaks were 46% less prevalent when IMPACT supplementation was part of the preoperative treatment.

CONCLUSION

This study identifies a dosage (0.5-1 l/day) and duration (supplementation for 5-7 days before surgery) of IMPACT that contributes to improved outcomes of morbidity in elective surgery patients, particularly those undergoing GI surgical procedures. The cost effectiveness of such practice is supported by recent health economic analysis. Findings suggest preoperative IMPACT use for the prophylaxis of postoperative complications in elective surgical patients.

Meta-analysis: anti-viral therapy of hepatitis C virus-related liver disease in renal transplant patients

BACKGROUND

The efficacy and safety of interferon-based therapy in renal transplant recipients with hepatitis C remains unclear, although a number of small clinical trials have been published addressing this issue.

AIM

To evaluate efficacy and safety of antiviral therapy with interferon (interferon alone or interferon plus ribavirin) in renal transplant patients with hepatitis C by performing a systematic review of the literature with a meta-analysis of clinical trials.

METHODS

The primary outcomes were sustained virological response (as a measure of efficacy) and/or drop-out rate (as a measure of tolerability). We used the random-effects model of DerSimonian and Laird, with heterogeneity and sensitivity analysis.

RESULTS

We identified 12 clinical trials (102 unique patients); there was one controlled study. The summary estimate for sustained virological response and drop-out rate was 18.0% (95% CI 7.0-29.0%) and 35.0% (95% CI 20-50%), respectively. The most frequent side-effect requiring interruption of treatment was graft dysfunction (n = 28; 71.7%). Meta-regression analysis showed an inverse and significant association between reference year and drop-out logit rate (P = 0.012); an inverse link between sustained virological response logit rate and frequency of hepatitis C virus genotype 1 (P = 0.067) and cirrhosis (P = 0.08) was found, even if no statistical significance was reached. No publication bias was observed.

CONCLUSIONS

Interferon-based therapy of hepatitis C has poor tolerance and safety after renal transplant. The optimal treatment of hepatitis C after renal transplant requires additional agents or alternative therapeutic approaches.

Possible effects on smokers of cigarette mentholation: a review of the evidence relating to key research questions

Menthol (2-isopropyl-5-methyl-cyclohexan-1-ol) is used in food, pharmaceutical, and tobacco products. Despite its long usage history and GRAS status, scientific literature on effects of cigarette mentholation is limited. Because African-American men have high lung cancer rates and predominantly smoke mentholated cigarettes, and because menthol's cooling effect might affect puffing and smoke inhalation, possible adverse effects of cigarette mentholation have been suggested. We review the evidence on the effects of mentholation on smokers, and we also identify areas for further study. Five large epidemiological studies provide no evidence that cigarette mentholation increases lung cancer risk. Mentholation cannot explain the higher risk for lung cancer in African-American male smokers, who also predominantly smoke mentholated cigarettes. Limited data on other cancers also suggest no risk from mentholation. The scientific literature suggests that cigarette mentholation does not increase puff number or puff volume of smoked cigarettes, and has little or no effect on heart rate, blood pressure, uptake of carbon monoxide, tar intake or retention, or blood cotinine concentration. Mentholation has little effect on other smoke constituents, and no apparent effect on nicotine absorption, airway patency and smoking initiation, dependency or cessation. Any toxicological effects of cigarette mentholation on adult smokers are probably quite limited.

Environmental Tobacco Smoke Exposure and Risk of Stroke in Nonsmokers: A Review With Meta-analysis

Our objective was to provide a comprehensive review of the epidemiologic evidence relating stroke to exposure to environmental tobacco smoke (passive smoking) in lifelong nonsmokers. In all, 7 prospective, 6 case-control, and 3 cross-sectional studies were identified that provided relevant information. The 16 studies varied considerably in design, exposure indices used, and disease definition. Based on 24 sex-specific relative risk estimates, and using current spousal exposure (or nearest equivalent) as the exposure index, meta-analysis gave an overall estimate of 1.25 (95% confidence interval 1.16-1.36), with no significant heterogeneity. There was no significant heterogeneity by sex, year of publication, fatality, or disease end point. There was some indication that relative risks were less elevated in prospective studies and in US or European studies. No elevation was seen for subarachnoid hemorrhage. The estimate was similar using ever rather than current exposure, or total rather than spousal exposure. Adjustment for risk factors other than age had no material effect on the estimate. Eight studies provided dose-response estimates, the combined relative risk for the highest level of exposure being 1.56 (95% confidence interval 1.34-1.82). Many studies have evident weaknesses, and recall bias and particularly publication bias are major concerns. Currently, the association is only suggestive of a possible causal relationship. A clearer picture could be obtained using data from existing very large prospective studies that have already provided risk estimates for passive smoking and heart disease, and by conducting large, well-designed studies of incident stroke.

Depression as a risk factor for the onset of type 2 diabetes mellitus. A meta-analysis

AIMS/HYPOTHESIS

Evidence strongly suggests that depression and type 2 diabetes are associated, but the direction of the association is still unclear. Depression may occur as a consequence of having diabetes, but may also be a risk factor for the onset of type 2 diabetes. This study examined the latter association by reviewing the literature and conducting a meta-analysis of longitudinal studies on this topic.

METHODS

Medline and PsycInfo were searched for articles published up to January 2005. All studies that examined the relationship between depression and the onset of type 2 diabetes were included. Pooled relative risks were calculated using fixed and random effects models. To explore sources of heterogeneity between studies, subgroup analyses and meta-regression analyses were performed.

RESULTS

Nine studies met our inclusion criteria for this meta-analysis. The pooled relative risk was 1.26 (1.13-1.39) using the fixed effects model and 1.37 (1.14-1.63) using the random effects model. Heterogeneity between studies could not be explained by (1) whether studies controlled for undetected diabetes at baseline; (2) the method of diabetes assessment at follow-up; (3) the baseline overall risk of diabetes in the study population; and (4) follow-up duration.

CONCLUSIONS/INTERPRETATION

Depressed adults have a 37% increased risk of developing type 2 diabetes mellitus. The pathophysiological mechanisms underlying this relationship are still unclear and warrant further research. A randomised controlled study is needed to test whether effective prevention or treatment of depression can reduce the incidence of type 2 diabetes and its health consequences.

Tests for differential gene expression using weights in oligonucleotide microarray experiments

Background

Microarray data analysts commonly filter out genes based on a number of ad hoc criteria prior to any high-level statistical analysis. Such ad hoc approaches could lead to conflicting conclusions with no clear guidance as to which method is most likely to be reproducible. Furthermore, the number of tests performed with concomitant inflation in type I error also plagues the statistical analysis of microarray data, since the number of tested quantities in a study significantly affects the family-wise error rate. It would, therefore, be very useful to develop and adopt strategies that allow quantification of the quality of each probeset, to filter out or give little credence to low-quality or unexpressed probesets, and to incorporate these strategies into gene selection within a multiple testing framework.

Results

We have proposed a unified scheme for filtering and gene selection. For Affymetrix gene expression microarrays, we developed new methods for measuring the reliability of a particular probeset in a single array, and we used these to develop measures for a set of arrays. These measures are then used as weights in standard t-statistic calculations, and are incorporated into the multiple testing procedures. We demonstrated the advantages of our methods using simulated data, publicly available spiked-in data as well as data comparing normal muscle to muscle from patients with Duchenne muscular dystrophy (DMD), in which a set of truly differentially expressed genes is known.

Conclusion

Our quality measures provide convenient ways to search for individual genes of high quality. The quality weighting strategies we proposed for testing differential gene expression have demonstrable improvement on the traditional filtering methods, the standard t-statistic and a regularized t-statistic in Affymetrix data analysis.

A metaanalysis of treatment outcomes of early enteral versus early parenteral nutrition in hospitalized patients

OBJECTIVE

Nutritional support as enteral or parenteral nutrition (PN) is used in hospitalized patients to reduce catabolism. This study compares outcomes of early enteral nutrition (EN) with early PN in hospitalized patients.

DESIGN

The authors conducted a metaanalysis of randomized, controlled trials (RCT) comparing early EN with PN. Studies on immunonutrition were excluded. Studies were categorized as medical, surgical, or trauma.

PATIENTS

RCTs of early EN/PN were identified by search of 1) MEDLINE (1966-2002), 2) published abstracts from scientific meetings, and 3) bibliographies of relevant articles.

MEASUREMENTS AND MAIN RESULTS

Thirty RCTs (ten medical, 11 surgical, and nine trauma) compared early EN with PN. The effect of nutrition type on hospital mortality and complication rates was reported as risk difference (RD%) and hospital length of stay (LOS) as mean weighted difference (MWD days). Missing data, by outcomes, varied from 20% to 63%. As a result of heterogeneity of treatment effects, the DerSimonian-Laird random-effects estimator was reported. There was no differential treatment effect of nutrition type on hospital mortality for all patients (0.6%, p = .4) and subgroups. PN was associated with increases in infective complications (7.9%, p = .001), catheter-related blood stream infections (3.5%, p = .003), noninfective complications (4.9%, p = .04), and hospital LOS (1.2 days, p = .004). There was no effect of nutrition type on technical complications (4.1%, p = .2). EN was associated with a significant increase in diarrheal episodes (8.7%, p = .001). Publication bias was not demonstrated. Metaanalytic regression analysis did not demonstrate any effect of age, time to initiate treatment, and average albumin on mortality estimates. Cumulative metaanalysis showed no change in the mortality estimates with time.

CONCLUSION

There was no mortality effect with the type of nutritional supplementation. Although early EN significantly reduced complication rates, this needs to be interpreted in the light of missing data and heterogeneity. The enthusiasm that early EN, as compared with early PN, would reduce mortality appears misplaced.

Does increased cigarette consumption nullify any reduction in lung cancer risk associated with low-tar filter cigarettes?

Epidemiological data suggest that smoking filter and lower tar cigarettes is associated with less lung cancer risk than is smoking plain and higher tar cigarettes. A recent National Cancer Institute monograph claimed these apparent benefits of lower delivery products may be illusory if relative risks are adjusted for daily consumption, and switching leads to "compensation" for reduced nicotine intake by increasing numbers of cigarettes smoked. To investigate this, we compared relative risks unadjusted and adjusted for daily cigarette consumption. Overall estimates of the filter/plain relative risk, using random-effects meta-analysis, were 0.61 (95%confidence interval 0.54 to 0.70) for unadjusted data and 0.66 (0.58 to 0.76) for adjusted data. The lower tar/higher tar relative risk was estimated as 0.60 (0.45 to 0.81) for unadjusted data and 0.73 (0.64 to 0.83) for adjusted data. The risk reductions were clearly seen regardless of gender, study location, period, or design, and when only studies providing both unadjusted and adjusted estimates were considered. Whether or not relative risk estimates are adjusted for cigarette consumption is not crucial to the conclusion of a clear advantage to filter cigarettes and tar reduction. Data on "compensation" for amount smoked were reviewed and any increase following switching to reduced-tar-yield cigarettes was shown to be quite small. Other biases in the epidemiology are also discussed, and we conclude that the apparent advantage to reduced-tar-delivery products is real and likely to be a marked underestimate of the reduction in lung cancer risk from lifetime smoking of low-tar cigarettes.