Evidence for excess colorectal cancer incidence among asbestos-exposed men in the Beta-Carotene and Retinol Efficacy Trial

Industrial pollution and mortality from digestive cancers at the small area level in a Spanish industrialized province

The province of Cadiz, Spain, is a highly industrialized area with numerous registered industrial plants, which has led to major concern regarding the possible influence of these facilities on the high rate of cancer-related mortality observed. Our objective was to evaluate the association between digestive cancer mortality and proximity to industrial installations in the province of Cadiz over the period 1992-2014 and to analyse this risk according to different categories of carcinogenic substances. An ecological study at the census tract level was carried out. Mortality due to digestive cancer (involving the oral cavity, pharynx, oesophagus, stomach, liver, pancreas, gallbladder, colon and rectum) was analysed. Using the spatial Besag, York and Mollié (BYM) approach, we assessed the relative risk of dying from these cancers for people living between 500 m and 5 km from industrial installations. The models were adjusted to account for socioeconomic deprivation. We detected a significant, excess risk of dying due to cancer in the following organs (expressed as relative risk with 95% confidence intervals): colon/rectum (1.13; 1.04-1.22 at 4 km), stomach (1.13; 1.00-1.29 at 2 km), liver (1.28; 1.02-1.61 at 1 km), pancreas (1.19; 1.03-1.39 at 2 km), oral and pharyngeal (1.40; 1.08-1.82 at 1 km), oesophagus (2.05; 1.18-3.56 at 500 m) and gallbladder (2.80; 1.14-6.89 at 500 m) for men; and from colorectal (1.21; 1.00-1.46 at 1 km), stomach (1.15; 1.01-1.31 at 4 km) and liver (1.58; 1.20- 2.07 at 1 km) cancers for women. The results support the hypothesis of an association between several digestive cancers and proximity to polluting industrial plants.

Association between shiftwork and the risk of colorectal cancer in females: a population-based case-control study

OBJECTIVE

Research indicates that shiftwork may be associated with increased risks of adverse health outcomes, including some cancers. However, the evidence of an association between shiftwork and colorectal cancer risk is limited and inconclusive. Further, while several possible pathways through which shiftwork might result in cancer have been proposed, few studies have taken these factors into account. We investigated the association between two types of shiftwork (graveyard shiftwork and early-morning shiftwork) and six mechanistic shiftwork variables (including light at night and phase shift) and the risk of colorectal cancer among females in an Australian population-based case-control study. Graveyard shiftwork was the primary exposure of interest.

METHODS

Participants (350 cases and 410 controls) completed a lifetime occupational history, and exposure to each of the eight shiftwork variables was assigned to participants through a job exposure matrix. We used logistic regression to calculate odds ratios (OR) and corresponding 95% confidence intervals (CI) for the association between different shiftwork variables and the risk of colorectal cancer, adjusting for potential demographic, lifestyle and medical confounders.

RESULTS

Working in an occupation involving long-term exposure (>7.5 years) to graveyard shiftwork was not associated with colorectal cancer risk (adjusted OR 0.95, 95% CI 0.57 to 1.58). Similarly, no increased risks of colorectal cancer were seen for any of the other seven shiftwork variables examined.

CONCLUSIONS

No evidence of an increased risk of colorectal cancer among females who had worked in occupations involving shiftwork was observed in this study.

Malignant Mesothelioma of the Pleuraand Other Malignancies in the Same Patient

Aims and background

The co-existence of mesothelioma, mostly asbestos-related, and other primary malignancies has repeatedly been reported. The present study evaluated the frequency of such an occurrence.

Methods

In the period October 1979-June 2002, 215 cases of malignant pleural mesothelioma were diagnosed at the Hospital of Monfalcone, Italy. All the cases of the above series, examined at necropsy (169), were included in the study. Occupational histories had been obtained from the patients or from their relatives by personal or telephone interviews. In 132 cases, asbestos bodies were isolated after chemical digestion of lung samples. The thoracic cavities were examined for pleural plaques.

Results

Additional malignancies were observed in 32 cases (18.9%). Multiple tumors were synchronous in 22 cases, metachronous in 8 cases, and synchronous and metachronous in 2. Four different tumors were found in 2 cases, 3 malignancies were detected in 6 patients, and 2 malignancies in the remaining 24. The most frequent additional malignancies were prostate adenocarcinoma (7 cases), non-Hodgkin lymphoma or chronic lymphocytic leukaemia (5 cases), bladder carcinoma (4 cases), kidney carcinoma (4 cases), large bowel carcinoma (4 cases), and liver cell carcinoma (4 cases). All the patients had histories of exposure to asbestos, mostly in shipbuilding. Lung asbestos body burdens ranged between 60 and 230,000 per gram of dried tissue. Pleural plaques were found in 26 cases.

Conclusions

In contrast with other series of the literature, in the present cases the co-existence of mesothelioma and other malignancies appeared as a relatively frequent event. The lack of a control group does not allow definite conclusions about the meaning of the occurrence. However, the co-existence of certain tumors with asbestos-related mesothelioma suggests that mesothelioma and associated malignancies might share some etiologic factors (asbestos and others).

Case–control study to assess the association between colorectal cancer and selected occupational agents using INTEROCC job exposure matrix

Background

Colorectal cancer is the third most prevalent cancer in the world and is twice as common in developed countries when compared with low-income and middle-income countries. Few occupational risk factors for colorectal cancer have been identified. This case–control study aimed to assess the association between colorectal cancer and occupational exposure to selected solvents, combustion products, metals, dusts and other agents.

Methods

Cases (n=918) were enrolled from the Western Australian Cancer Registry from June 2005 to August 2007. Controls (n=1021) were randomly selected from the Western Australian electoral roll. We collected lifetime occupational history from cases and controls, in addition to their demographic and lifestyle characteristics. We applied the INTEROCC job exposure matrix to convert the occupational history to occupational exposure for 18 selected agents. Three exposure indices were developed: (1) exposed versus non-exposed; (2) lifetime cumulative exposure; and (3) total duration of exposure. The associations between colorectal cancer and the selected agents were estimated using logistic regression models adjusting for sex and age.

Results

None of the 18 selected agents showed an association with colorectal cancer. No dose–response relationships with lifetime cumulative exposure or duration of exposure were observed.

Conclusion

There was no evidence to suggest that occupational exposure to 18 selected agents increased the risk of colorectal cancer.

Occupational Asbestos Exposure and Incidence of Colon and Rectal Cancers in French Men: The Asbestos-Related Diseases Cohort (ARDCo-Nut)

BACKGROUND

The relationships between asbestos exposure and colorectal cancer remain controversial.

OBJECTIVES

We examined the association between asbestos exposure and colorectal cancer incidence.

METHODS

Volunteer retired workers previously exposed to asbestos were invited to participate in the French ARDCo screening program between 2003 and 2005. Additional data on risk factors for colorectal cancer were collected from the ARDCo-Nut subsample of 3,769 participants in 2011. Cases of colon and rectal cancer were ascertained each year through 2014 based on eligibility for free medical care following a cancer diagnosis. Survival regression based on the Cox model was used to estimate the relative risk of colon and rectal cancer separately, in relation to the time since first exposure (TSFE) and cumulative exposure index (CEI) to asbestos, and with adjustment for smoking in the overall cohort and for smoking, and certain risk factors for these cancers in the ARDCo-Nut subsample.

RESULTS

Mean follow-up was 10.2 years among 14,515 men, including 181 colon cancer and 62 rectal cancer cases (41 and 17, respectively, in the ARDCo-Nut subsample). In the overall cohort, after adjusting for smoking, colon cancer was significantly associated with cumulative exposure (HR = 1.14; 95% CI: 1.04, 1.26 for a 1-unit increase in ln-CEI) and ≥ 20-40 years since first exposure (HR = 4.67; 95% CI: 1.92, 11.46 vs. 0-20 years TSFE), and inversely associated with 60 years TSFE (HR = 0.26; 95% CI: 0.10, 0.70). Although rectal cancer was also associated with TSFE 20-40 years (HR = 4.57; 95% CI: 1.14, 18.27), it was not associated with ln-CEI, but these findings must be interpreted cautiously due to the small number of cases.

CONCLUSIONS

Our findings provide support for an association between occupational exposure to asbestos and colon cancer incidence in men. Citation: Paris C, Thaon I, Hérin F, Clin B, Lacourt A, Luc A, Coureau G, Brochard P, Chamming's S, Gislard A, Galan P, Hercberg S, Wild P, Pairon JC, Andujar P. 2017. Occupational asbestos exposure and incidence of colon and rectal cancers in French men: the Asbestos-Related Diseases Cohort (ARDCo-Nut). Environ Health Perspect 125:409-415; http://dx.doi.org/10.1289/EHP153.

Asbestos-Induced Gastrointestinal Cancer: An Update

Asbestos-related diseases, such as malignancies and asbestosis, remain a significant occupational and public health concern. Asbestos is still widely used in many developing countries despite being a recognized carcinogen that has been banned over 50 countries. The prevalence and mortality from asbestos-related diseases continue to pose challenges worldwide. Many countries are now experiencing an epidemic of asbestos-related disease that is the legacy of occupational exposure during the 20th century because of the long latency period (up to 40 years) between initial asbestos exposure and exhibition of disease. However, the gastrointestinal (GI) cancers resulting from asbestos exposure are not as clearly defined. In this review, we summarize some of the recent epidemiology of asbestos-related diseases and then focus on the evidence implicating asbestos in causing GI malignancies. We also briefly review the important new pathogenic information that has emerged over the past several years that may account for asbestos-related gastrointestinal cancers. All types of asbestos fibers have been implicated in the mortality and morbidity from GI malignancies but the collective evidence to date is mixed. Although the molecular basis of GI cancers arising from asbestos exposure is unclear, there have been significant advances in our understanding of mesothelioma and asbestosis that may contribute to the pathophysiology underlying asbestos-induced GI cancers. The emerging new evidence into the pathogenesis of asbestos toxicity is providing insights into the molecular basis for developing novel therapeutic strategies for asbestos-related diseases in future management.

[Colorectal cancer in Spain: Temporary disability and preventive occupational strategies]

BACKGROUND

Colorectal cancer is one of the most frequent cancers in both sexes and the most frequent in the developed countries, if men and women are considered together as a group. It has an important associated morbidity and mortality in all countries and constitutes a public health problem with a high direct and indirect economic cost. The number of workdays lost due to temporary disability (TD) is one of the quantifiable references of these indirect costs.

AIMS

To determine the indirect cost associated with TD due to colorectal cancer in Spain during the year 2011, a cost that aids in the prevention cost/benefit estimation.

METHODS

The number of TD processes, the number of workdays lost due to TD, and the mean duration of those processes, based on the CIE 9-MC codes related to this pathology, as well as the calculated cost, using the Spanish minimum wage as a reference, during the period of January to December 2011, were all reviewed.

RESULTS

Colorectal cancer in Spain during 2011 represented 1,046 TD processes, 202,784 workdays lost, and a mean process duration of 194 days/year. The resulting cost of the pathology due to TD was 4,335,521.92 euros.

CONCLUSIONS

These results are beneficial for evaluating the usefulness of implementing public health support strategies for a greater reduction in colorectal cancer prevalence and mortality, and an improvement in quality of life of the affected individuals and their families, together with an economic savings resulting from a reduction in TD as a consequence of this disease.

All-cause mortality and cancer incidence among adults exposed to blue asbestos during childhood

BACKGROUND

There are few data on the long-term health outcomes of exposure to asbestos in childhood. This study investigated cancer and mortality of adults exposed to blue asbestos as children.

METHODS

Data linkage to relevant health registries was used to identify cancers and mortality in a cohort of adults (n = 2,460) that had lived in an asbestos mining town during their childhood (<15 years).

RESULTS

There were 217 (93 female) incident cancers and 218 (70 female) deaths among the cohort. Compared with the Western Australian population females had elevated mesothelioma, ovarian and brain cancers, and increased "all cause" and "all cancer" mortality. Males had elevated mesothelioma, leukemia, prostate, brain, and colorectal cancers, and excess mortality from "all causes," "all cancers," circulatory disease, diseases of the nervous system, and accidents.

CONCLUSION

Exposure to blue asbestos in childhood is associated with an increased risk of cancer and mortality in adults.

Vitamin A (retinol) downregulates the receptor for advanced glycation endproducts (RAGE) by oxidant-dependent activation of p38 MAPK and NF-kB in human lung cancer A549 cells

As an essential component of the diet, retinol supplementation is often considered harmless and its application is poorly controlled. However, recent works demonstrated that retinol may induce a wide array of deleterious effects, especially when doses used are elevated. Controlled clinical trials have demonstrated that retinol supplementation increased the incidence of lung cancer and mortality in smokers. Experimental works in cell cultures and animal models showed that retinol may induce free radical production, oxidative stress and extensive biomolecular damage. Here, we evaluated the effect of retinol on the regulation of the receptor for advanced glycation end-products (RAGE) in the human lung cancer cell line A549. RAGE is constitutively expressed in lungs and was observed to be down-regulated in lung cancer patients. A549 cells were treated with retinol doses reported as physiologic (2 μM) or therapeutic (5, 10 or 20 μM). Retinol at 10 and 20 μM increased free radical production, oxidative damage and antioxidant enzyme activity in A549 cells. These doses also downregulated RAGE expression. Antioxidant co-treatment with Trolox®, a hydrophilic analog of α-tocopherol, reversed the effects of retinol on oxidative parameters and RAGE downregulation. The effect of retinol on RAGE was mediated by p38 MAPK activation, as blockade of p38 with PD169316 (10 μM), SB203580 (10 μM) or siRNA to either p38α (MAPK14) or p38β (MAPK11) reversed the effect of retinol on RAGE. Trolox also inhibited p38 phosphorylation, indicating that retinol induced a redox-dependent activation of this MAPK. Besides, we observed that NF-kB acted as a downstream effector of p38 in RAGE downregulation by retinol, as NF-kB inhibition by SN50 (100 μg/mL) and siRNA to p65 blocked the effect of retinol on RAGE, and p38 inhibitors reversed NF-kB activation. Taken together, our results indicate a pro-oxidant effect of retinol on A549 cells, and suggest that modulation of RAGE expression by retinol is mediated by the redox-dependent activation of p38/NF-kB signaling pathway.

Colorectal cancer mortality and industrial pollution in Spain

Background

Records kept as a result of the implementation of Integrated Pollution Prevention and Control (IPPC) and the European Pollutant Release and Transfer Register (E-PRTR) constitute a public inventory of industries, created by the European Commission, which is a valuable resource for monitoring industrial pollution. Our objective is to ascertain whether there might be excess colorectal cancer mortality among populations residing in the vicinity of Spanish industrial installations that are governed by the IPPC Directive and E-PRTR Regulation and report their emissions to air.

Methods

An ecological study was designed to examine colorectal cancer mortality at a municipal level (8098 Spanish towns), over the period 1997–2006. We conducted an exploratory "near vs. far" analysis to estimate the relative risks (RR) of towns situated at a distance of less than 2 km from industrial installations. The analysis was repeated for each of the 24 industrial groups. RR and their 95% credible/confidence intervals (95%CI) were estimated on the basis of Poisson regression models, using two types of modelling: a) the conditional autoregressive Bayesian model proposed by Besag, York and Mollié, with explanatory variables; and b) a mixed regression model. Integrated nested Laplace approximations were used as a Bayesian inference tool.

Results

Statistically significant RRs were detected in the vicinity of mining industry (RR 1.258; 95%CI 1.082 - 1.463), paper and wood production (RR 1.071; 95%CI 1.007 – 1.140), food and beverage sector (RR 1.069; 95%CI 1.029 - 1.111), metal production and processing installations (RR 1.065; 95% CI 1.011 – 1.123) and ceramics (RR 1.050 ; 95%CI 1.004 – 1.099).

Conclusions

Given the exploratory nature of this study, it would seem advisable to check in other countries or with other designs, if the proximity of industries that emit pollutants into the air could be an added risk factor for colorectal cancer mortality. Nevertheless, some of the differences between men and women observed in the analyses of the industrial groups suggest that there may be a component of occupational exposure, little-studied in the case of cancers of the digestive system.

L-NAME co-treatment prevent oxidative damage in the lung of adult Wistar rats treated with vitamin A supplementation

Based on the fact that vitamin A in clinical doses is a potent pro-oxidant agent to the lungs, we investigated here the role of nitric oxide (NO•) in the disturbances affecting the lung redox environment in vitamin A-treated rats (retinol palmitate, doses of 1000-9000 IU•kg(-1)•day(-1)) for 28 days. Lung mitochondrial function and redox parameters, such as lipid peroxidation, protein carbonylation and the level of 3-nytrotyrosine, were quantified. We observed, for the first time, that vitamin A supplementation increases the levels of 3-nytrotyrosine in rat lung mitochondria. To determine whether nitric oxide (NO •) or its derivatives such as peroxynitrite (ONOO-) was involved in this damage, animals were co-treated with the nitric oxide synthase inhibitor L-NAME (30 mg•kg(-1), four times a week), and we analysed if this treatment prevented (or minimized) the biochemical disturbances resulting from vitamin A supplementation. We observed that L-NAME inhibited some effects caused by vitamin A supplementation. Nonetheless, L-NAME was not able to reverse completely the negative effects triggered by vitamin A supplementation, indicating that other factors rather than only NO• or ONOO- exert a prominent role in mediating the redox effects in the lung of rats that received vitamin A supplementation.

Identification of occupational cancer risks in British Columbia, Canada: a population-based case-control study of 1,155 cases of colon cancer

Objective

Cancer has been recognized to have environmental origin, but occupational cancer risk studies have not been fully documented. The objective of this paper was to identify occupations and industries with elevated colon cancer risk based on lifetime occupational histories collected from 15,463 incident cancer cases.

Method

A group matched case-control design was used. All cases were diagnosed with histologically proven colon cancers, with cancer controls being all other cancer sites, excluding rectum, lung and unknown primary, diagnosed at the same period of time from the British Columbia Cancer Registry. Data analyses were done on all 597 Canadian standard occupation titles and 1,104 standard industry titles using conditional logistic regression for matched data sets and the likelihood ratio test.

Results

Excess colon cancer risks was observed in a number of occupations and industries, particularly those with low physical activity and those involving exposure to asbestos, wood dusts, engine exhaust and diesel engine emissions, and ammonia.

Discussion

The results of our study are in line with those from the literature and further suggest that exposure to wood dusts and to ammonia may carry an increased occupational risk of colon cancer.

Occupational asbestos exposure and digestive cancers - a cohort study

BACKGROUND

Although the role of asbestos in the genesis of mesothelioma and primary bronchopulmonary cancers has been established, results from studies focusing on the relationship between occupational exposure to asbestos and digestive cancer remain contradictory.

AIM

To determine whether occupational asbestos exposure increases the incidence of digestive cancers.

METHODS

Our study was a retrospective morbidity study based on 2024 subjects occupationally exposed to asbestos. The incidence of digestive cancer was calculated from 1st January 1978 to 31st December 2004 and compared with levels among the local general population using Standardized Incidence Ratios. Asbestos exposure was assessed using the company's job exposure matrix.

RESULTS

Eighty-five cases of digestive cancer were observed within our cohort, for an expected number of 66.90 (SIR = 1.27 [1.01; 1.57]). A significantly elevated incidence, particularly notable among women, was observed for peritoneal mesothelioma, independently of exposure levels. A significantly elevated incidence was also noted among men for cancer of small intestine and oesophagus, for cumulative exposure indexes for asbestos above 80 fibres/mL x years. A significantly elevated incidence of cancer of the small intestine was also observed among men having been exposed to asbestos for periods in excess of 25 years and for mean exposure levels in excess of 4 fibres/mL.

CONCLUSIONS

This study suggests the existence of a relationship between exposure to asbestos and cancer of the small intestine and of the oesophagus in men.

Antioxidant supplements for preventing gastrointestinal cancers

BACKGROUND

Oxidative stress may cause gastrointestinal cancers. The evidence on whether antioxidant supplements are effective in preventing gastrointestinal cancers is contradictory.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements in preventing gastrointestinal cancers.

SEARCH STRATEGY

We identified trials through the trials registers of the four Cochrane Review Groups on gastrointestinal diseases, The Cochrane Central Register of Controlled Trials in The Cochrane Library (Issue 2, 2007), MEDLINE, EMBASE, LILACS, SCI-EXPANDED, and The Chinese Biomedical Database from inception to October 2007. We scanned reference lists and contacted pharmaceutical companies.

SELECTION CRITERIA

Randomised trials comparing antioxidant supplements to placebo/no intervention examining occurrence of gastrointestinal cancers.

DATA COLLECTION AND ANALYSIS

Two authors (GB and DN) independently selected trials for inclusion and extracted data. Outcome measures were gastrointestinal cancers, overall mortality, and adverse effects. Outcomes were reported as relative risks (RR) with 95% confidence interval (CI) based on random-effects and fixed-effect model meta-analysis. Meta-regression assessed the effect of covariates across the trials.

MAIN RESULTS

We identified 20 randomised trials (211,818 participants), assessing beta-carotene (12 trials), vitamin A (4 trials), vitamin C (8 trials), vitamin E (10 trials), and selenium (9 trials). Trials quality was generally high. Heterogeneity was low to moderate. Antioxidant supplements were without significant effects on gastrointestinal cancers (RR 0.94, 95% CI 0.83 to 1.06). However, there was significant heterogeneity (I(2) = 54.0%, P = 0.003). The heterogeneity may have been explained by bias risk (low-bias risk trials RR 1.04, 95% CI 0.96 to 1.13 compared to high-bias risk trials RR 0.59, 95% CI 0.43 to 0.80; test of interaction P < 0.0005), and type of antioxidant supplement (beta-carotene potentially increasing and selenium potentially decreasing cancer risk). The antioxidant supplements had no significant effects on mortality in a random-effects model meta-analysis (RR 1.02, 95% CI 0.97 to 1.07, I(2) = 53.5%), but significantly increased mortality in a fixed-effect model meta-analysis (RR 1.04, 95% CI 1.02 to 1.07). Beta-carotene in combination with vitamin A (RR 1.16, 95% CI 1.09 to 1.23) and vitamin E (RR 1.06, 95% CI 1.02 to 1.11) significantly increased mortality. Increased yellowing of the skin and belching were non-serious adverse effects of beta-carotene. In five trials (four with high risk of bias), selenium seemed to show significant beneficial effect on gastrointestinal cancer occurrence (RR 0.59, 95% CI 0.46 to 0.75, I(2) = 0%).

AUTHORS' CONCLUSIONS

We could not find convincing evidence that antioxidant supplements prevent gastrointestinal cancers. On the contrary, antioxidant supplements seem to increase overall mortality. The potential cancer preventive effect of selenium should be tested in adequately conducted randomised trials.

Iron intake, oxidative stress-related genes (MnSOD and MPO) and prostate cancer risk in CARET cohort

Iron overload may increase prostate cancer risk through stimulation of oxidative stress, and endogenous pro- and antioxidant capabilities, i.e. manganese superoxide dismutase (MnSOD) and myeloperoxidase (MPO), may modify these associations. We investigated this hypothesis in the Carotene and Retinol Efficacy Trial cohort in a nested case-control study. Although there was no association between iron intake and risk overall, there was a suggestion of increased risk of clinically aggressive prostate cancer with higher iron intake [odds ratio (OR) = 1.4, 95% confidence interval (CI) = 0.9-2.0]. Associations were most notable for men with aggressive prostate cancer who were below the median consumption of total fruits and vegetables (OR = 1.8, 95% CI = 1.1-3.2). Associations between MPO -463 G to A genotype (rs2333227) and prostate cancer risk were only noted among men with aggressive cancer, with more than a 2-fold risk reduction among men with AA genotypes (OR = 0.4, 95% CI = 0.2-1.0); MnSOD was not associated with risk overall, but the MnSOD T to C (Val-9Ala, rs4880) polymorphism modified associations between risk of clinically aggressive prostate cancer and dietary iron intake (P for interaction = 0.02). Among aggressive cancer cases with the TT genotype, higher iron intake level was associated with >2-fold increase in risk (OR = 2.3, 95% CI = 1.0-4.9), whereas there was no association among men with CC genotypes (OR = 0.9, 95% CI = 0.4-2.3). Although interactions were not significant, there were similar patterns for MPO genotype, iron intake and risk. These findings suggest that higher iron intake may be associated with risk of clinically aggressive prostate cancer, and that endogenous antioxidant capabilities may modify these associations.

Antioxidant supplements for preventing gastrointestinal cancers

BACKGROUND

Oxidative stress may cause gastrointestinal cancers. The evidence on whether antioxidant supplements are effective in preventing gastrointestinal cancers is contradictory.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements in preventing gastrointestinal cancers.

SEARCH STRATEGY

We identified trials through the trials registers of the four Cochrane Review Groups on gastrointestinal diseases, The Cochrane Central Register of Controlled Trials on The Cochrane Library (Issue 1, 2003), MEDLINE, EMBASE, LILACS, and SCI-EXPANDED from inception to February 2003, and The Chinese Biomedical Database (March 2003). We scanned reference lists and contacted pharmaceutical companies.

SELECTION CRITERIA

Randomised trials comparing antioxidant supplements to placebo/no intervention examining the incidence of gastrointestinal cancers.

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected trials for inclusion and extracted data. The outcome measures were incidence of gastrointestinal cancers, overall mortality, and adverse events. Outcomes were reported as relative risks (RR) with 95% confidence interval (CI) based on fixed and random effects meta-analyses.

MAIN RESULTS

We identified 14 randomised trials (170,525 participants), assessing beta-carotene (9 trials), vitamin A (4 trials), vitamin C (4 trials), vitamin E (5 trials), and selenium (6 trials). Trial quality was generally high. Heterogeneity was low to moderate. Neither the fixed effect (RR 0.96, 95% CI 0.88 to 1.04) nor random effects meta-analyses (RR 0.90, 95% CI 0.77 to 1.05) showed significant effects of supplementation with antioxidants on the incidences of gastrointestinal cancers. Among the seven high-quality trials reporting on mortality (131,727 participants), the fixed effect (RR 1.06, 95% CI 1.02 to 1.10) unlike the random effects meta-analysis (RR 1.06, 95% CI 0.98 to 1.15) showed that antioxidant supplements significantly increased mortality. Two low-quality trials (32,302 participants) found no significant effect of antioxidant supplementation on mortality. The difference between the mortality estimates in high- and low-quality trials was significant by test of interaction (z = 2.10, P = 0.04). Beta-carotene and vitamin A (RR 1.29, 95% CI 1.14 to 1.45) and beta-carotene and vitamin E (RR 1.10, 95% CI 1.01 to 1.20) significantly increased mortality, while beta-carotene alone only tended to do so (RR 1.05, 95% CI 0.99 to 1.11). Increased yellowing of the skin and belching were non-serious adverse effects of beta-carotene. In four trials (three with unclear/inadequate methodology), selenium showed significant beneficial effect on gastrointestinal cancer incidences.

REVIEWERS' CONCLUSIONS

We could not find evidence that antioxidant supplements prevent gastrointestinal cancers. On the contrary, they seem to increase overall mortality. The potential cancer preventive effect of selenium should be studied in adequately conducted randomised trials.