Effects of supplemental alpha-tocopherol and beta-carotene on colorectal cancer: results from a controlled trial (Finland)

Association between β-carotene supplementation and risk of cancer: a meta-analysis of randomized controlled trials

CONTEXT

β-Carotene, which is derived from most fruits and vegetables, is the most common type of carotenes. Existing studies have demonstrated that β-carotene is associated with some positive health outcomes. However, results about the effects of supplemental β-carotene on cancer are inconsistent.

OBJECTIVE

To determine the association between supplemental β-carotene intake and the risk of cancers.

DATA SOURCES

Eight databases (PubMed, Web of Science, Embase, Cochrane, China National Knowledge Infrastructure, Wangfang, China Science and Technology Journal Database, and Chinese Biomedical Literature Database) were systematically searched until September 2022.

DATA EXTRACTION

Only reports from randomized controlled trials in which an association between supplemental β-carotene intake and the risk of cancer was found were included in the meta-analysis.

DATA ANALYSIS

A total of 18 eligible studies based on 8 different randomized controlled trials were included in the meta-analysis, with varying sample sizes from 391 to 39 876 participants. There was no significant association between supplemental β-carotene intake and overall cancer incidence rate after synthesizing all the results (risk ratio [RR]: 1.02; 95% confidence interval [CI], 0.99-1.05). Results from subgroup analysis indicated that intake of supplemental β-carotene significantly increased the risk of lung cancer (RR: 1.19; 95%CI: 1.08-1.32), whereas no significant associations were observed for other site-specific cancers. In addition, smokers and the subgroup of participants with only low-dose β-carotene intake had a risk increment of cancer if they took supplemental β-carotene (RR: 1.16; 95%CI: 1.05-1.29).

CONCLUSION

β-Carotene supplementation has no beneficial or harmful effect on cancer incidence; moreover, it might have potentially harmful effects on lung cancer, especially for people who smoke. On the basis of the evidence from this study, supplemental intake of β-carotene is not recommended for preventing cancer, and the establishment of a tolerable upper intake level of β-carotene should be considered.

An overview of vitamins as epidrugs for colorectal cancer prevention

Gene expression altering epigenomic modifications such as DNA methylation, histone modification, and chromosome remodeling is crucial to regulating many biological processes. Several lifestyle factors, such as diet and natural, bioactive food compounds, such as vitamins, modify epigenetic patterns. However, epigenetic dysregulation can increase the risk of many diseases, including cancer. Various studies have provided supporting and contrasting evidence on the relationship between vitamins and cancer risk. Though there is a gap in knowledge about whether dietary vitamins can induce epigenetic modifications in the context of colorectal cancer (CRC), the possibility of using them as epidrugs for CRC treatment is being explored. This is promising because such studies might be informative about the most effective way to use vitamins in combination with DNA methyltransferase inhibitors and other approved therapies to prevent and treat CRC. This review summarizes the available epidemiological and observational studies involving dietary, circulating levels, and supplementation of vitamins and their relationship with CRC risk. Additionally, using available in vitro, in vivo, and human observational studies, the role of vitamins as potential epigenetic modifiers in CRC is discussed. This review is focused on the action of vitamins as modifiers of DNA methylation because aberrant DNA methylation, together with genetic alterations, can induce the initiation and progression of CRC. Although this review presents some studies with promising results, studies with better study designs are necessary. A thorough understanding of the underlying molecular mechanisms of vitamin-mediated epigenetic regulation of CRC genes can help identify effective therapeutic targets for CRC prevention and treatment.

The efficacy of chemopreventive agents on the incidence of colorectal adenomas: A systematic review and network meta-analysis

Colorectal cancer (CRC) is the fourth most common cancer and third leading cause of cancer-related death worldwide. Use of chemopreventive agents (CPAs) to reduce the incidence of precursor colorectal adenomas could lower the future burden of CRC. Many classes of potential CPAs have been investigated. To identify the most effective CPAs, we conducted a systematic review and a network meta-analysis (NMA). An electronic search was performed through August 2020 to identify all randomized controlled trials (RCTs) assessing the efficacy of CPAs in reducing the incidence of colorectal adenomas at the time of surveillance colonoscopy among patients who had previously undergone polypectomy during an index colonoscopy. In total, 33 RCTs were included in the NMA, which was conducted under a Bayesian inference framework. Random effects models were used with adjustment for follow-up length and control group event rates to yield relative risks (RRs) and 95% credible intervals (CrIs). Our full network consisted of 13 interventions in addition to a placebo arm. Of 20,925 included patients, 7766 had an adenoma. Compared to placebo, the combination of difluoromethylornithine (DFMO) + Sulindac (RR 0.24, CrI 0.10-0.55) demonstrated a protective effect, while aspirin had a RR of 0.77 (CrI 0.60-1.00), celecoxib 800 mg had a RR of 0.56 (CrI 0.31-1.01) and metformin had a RR of 0.56 (CrI 0.22-1.39). Our results suggest that select CPAs may be efficacious in preventing the development of adenomas. Further studies are needed to identify those patients most likely to benefit and the minimum effective dosages of CPAs.

Association Between Beta-Carotene Supplementation and Mortality: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background

Aging is a phenomenon universally involving all organisms, genetically determined, and epigenetically influenced by the environment. Numerous observational studies have shown the positive impact of non-pharmacological approaches started in younger age on chronic conditions affecting the elderly health and survival. This meta-analysis aimed to investigate the effect of beta-carotene on the total and cause-specific mortality as reported by randomized controlled trials (RCTs).

Methods

We searched Medline, Scopus, Web of Science, and CENTRAL Cochrane from inception to September 2021. Studies were eligible if enrolled adults with any health condition, compared beta-carotene supplements at any dose with placebo or no intervention, provided information on deaths from any cause, and were RCTs, in English. The risk of bias was assessed by the Cochrane risk of bias tool and the GRADE. Risk ratios and their 95% confidence intervals were used and a P-value less than 0.05 was considered statistically significant.

Results

Among 3,942 articles searched, 44 articles on 31 RCTs, which included 216,734 total subjects, 108,622 in beta-carotene supplement groups, and 108,112 in the placebo or no-intervention groups, were involved in the final analyses. In a random-effects meta-analysis of all 31 trials, beta-carotene supplements were found to have no preventive effect on mortality (risk ratio 1.02, 95% confidence interval 0.98–1.05, I2 = 42%). Further, the analysis showed no preventive effect on cancer, cardiovascular, cerebrovascular, and other mortality causes. Instead, beta-carotene supplementation significantly increased the risk of lung cancer mortality (RR 1.14, 95% CI 1.02, 1.27, I2 = 3%) but decreased the risk of human immunodeficiency virus-related mortality (RR 0.55, 95% CI 0.33, 0.92, I2 = 0).

Conclusion

More studies should be performed to better define the role of beta-carotene on survival, to confirm or deny our results. Therefore, the possible beneficial or harmful effects of the beta-carotene supplementation on mortality must not be overstated.

Systematic Review Registration

[https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=259354], identifier [CRD42021259354].

Composite dietary antioxidant index and the risk of colorectal cancer: Findings from the Singapore Chinese Health Study

Colorectal cancer (CRC) is a major contributor to cancer death globally. Several studies showed some protections by certain individual dietary antioxidants against CRC development. Epidemiologic data on the composite dietary antioxidant index (CDAI) in relation to CRC risk are sparse. Using the Singapore Chinese Health Study, an ongoing prospective cohort consisting of 61 321 cancer-free participants aged 45 to 74 years at baseline, a food-based CDAI was calculated according to a previously established and validated method that included six food-sourced antioxidants including vitamins A, C and E, manganese, selenium and zinc. Cox proportional hazard regression method was used to estimate the hazard ratios (HRs) and their 95% confidence intervals (CIs) for CRC associated with various levels of CDAI with adjustment for multiple potential confounders. After an average of 17.5 years of follow-up, 2140 participants developed CRC. HRs (95% CIs) of CRC for quartiles 2, 3 and 4 of CDAI were 0.94 (0.83-1.07), 0.86 (0.75-1.00) and 0.80 (0.66-0.98), respectively, compared to the lowest quartile (P_trend  = .02). This inverse association between CDAI and CRC risk was more apparent in women or those without a history of diabetes, without family history of CRC, never smokers or overweight/obese individuals. However, none of the heterogeneity tests for the CDAI-CRC risk association reached statistical significance. Our findings suggest that food-based antioxidants may be beneficial for reducing the risk of CRC in the general population.

Preventing Colitis-Associated Colon Cancer With Antioxidants: A Systematic Review

Inflammatory bowel disease (IBD) patients have an increased risk of developing colitis-associated colon cancer (CAC); however, the basis for inflammation-induced genetic damage requisite for neoplasia is unclear. Several studies have shown that IBD patients have signs of increased oxidative damage, which could be a result of genetic and environmental factors such as an excess in oxidant molecules released during chronic inflammation, mitochondrial dysfunction, a failure in antioxidant capacity, or oxidant promoting diets. It has been suggested that chronic oxidative environment in the intestine leads to the DNA lesions that precipitate colon carcinogenesis in IBD patients. Indeed, several preclinical and clinical studies show that different endogenous and exogenous antioxidant molecules are effective at reducing oxidation in the intestine. However, most clinical studies have focused on the short-term effects of antioxidants in IBD patients but not in CAC. This review article examines the role of oxidative DNA damage as a possible precipitating event in CAC in the context of chronic intestinal inflammation and the potential role of exogenous antioxidants to prevent these cancers.

Efficacy and safety of chemopreventive agents on colorectal cancer incidence and mortality: systematic review and network meta-analysis

Background

Various interventions have been tested as primary prevention of colorectal cancers (CRC), but comprehensive evidence comparing them is absent. We examined the effects of various chemopreventive agents (CPAs) on CRC incidence and mortality.

Methods

We did a network meta-analysis based on a systematic review of randomized controlled trials (RCTs) that compared at least one CPA (aspirin, antioxidants, folic acid, vitamin B6, vitamin B12, calcium, vitamin D, alone or in combination) to placebo or other CPA in persons without history of CRC. Several databases were searched from inception up to March 2017. Primary outcomes were early and long-term CRC incidence and mortality.

Results

Twenty-one RCTs comprising 281,063 participants, 9 RCTS comprising 160,101 participants, and 7 RCTs comprising 24,001 participants were included in the network meta-analysis for early risk of CRC incidence, long-term risk of CRC incidence and mortality, respectively. For early CRC incidence, no CPAs were found to be effective. For long-term CRC incidence and mortality, aspirin was the only intervention that showed protective effects with potential dose-dependent effects (risk ratio [RR], 0.74 [95% CI, 0.57–0.97] for high-dose [≥325 mg/day] and RR, 0.81 [95% CI, 0.67–0.98] for very-low-dose [≤100 mg/day]). Similar trend was found for mortality (RR, 0.43 [95% CI, 0.23–0.81] for low-dose [>100–325 mg/day] and RR, 0.65 [95% CI, 0.45–0.94] for very-low-dose). However, in net clinical benefit analysis, when combining risk estimates on mortality from CRC, cardiovascular disease, and pooled risk estimates of major gastrointestinal bleeding, low-dose aspirin provided the highest net survival gain (%) of 1.736 [95% CI, 1.010–2.434].

Conclusion

Aspirin at the dose range of 75–325 mg/day is a safe and effective primary prevention for long-term CRC among people at average risk. None of the other CPAs were found to be effective. There may potentially be differential effects among various doses of aspirin that needs further investigation.

Carotenoid intake from natural sources and colorectal cancer: a systematic review and meta-analysis of epidemiological studies

Carotenoid intake from natural sources has been hypothesized to reduce the risk of colorectal cancer (CRC). The aim of this study was to systematically review the epidemiological evidence for the association between carotenoid intake from natural sources and CRC development. We carried out a systematic review and meta-analysis of epidemiological studies to investigate whether the intake of specific carotenoids from natural sources, as well as combined carotenoids, is associated with the risk of CRC overall and by anatomic subsite. A comprehensive literature search of MEDLINE and Scopus databases was performed. Twenty-two articles were identified from the literature search, of which 16 were case-control studies and 6 were cohort studies. In the random-effects meta-analysis of case-control and cohort studies, we found no association between the intake of individual and total carotenoids and the risk of CRC overall and by anatomic subsite. Overall, our findings do not support a significant association between intake of specific carotenoids from dietary sources, as well as combined carotenoids, and the risk of CRC overall and by anatomic subsite.

Antioxidant intake from diet and supplements and risk of digestive cancers in middle-aged adults: results from the prospective NutriNet-Santé cohort

Experimental studies suggest beneficial effects of antioxidants in digestive cancer prevention. However, epidemiological results are contrasting and few studies quantitatively assessed supplemental intake. This study aimed at investigating the associations between antioxidant intakes (dietary, supplemental and total) and digestive cancer risk. This prospective study included 38 812 middle-aged subjects (≥45 years) from the NutriNet-Santé cohort (2009-2016). Dietary data were collected using repeated 24 h records. A specific questionnaire assessed dietary supplement use over a 12-month period. A composition database of about 8000 dietary supplements was developed. Associations between continuous and sex-specific quartiles of vitamins C and E, β-carotene and Se intakes and digestive cancer risk were characterised using multivariable Cox proportional hazard models. A total of 167 incident digestive cancers (120 colorectal, twenty-six pancreatic, nine oesophagus, seven stomach and five liver) were diagnosed during follow-up investigation. Dietary (hazard ratios (HR)Q4 v. Q1=0·56; 95 % CI 0·34, 0·91, P trend=0·01) and total (HRQ4 v. Q1=0·51; 95 % CI 0·30, 0·84, P trend=0·008) vitamin C intakes, dietary (HRQ4 v. Q1=0·56; 95 % CI 0·34, 0·92, P trend=0·005) and total (HRQ4 v. Q1=0·58; 95 % CI 0·36, 0·94, P trend=0·003) vitamin E intakes, and dietary (HRfor an increment of 10 µg/d=0·92; 95 % CI 0·85, 1·00, P=0·04) and total (HRfor an increment of 10 µg/d=0·92; 95 % CI 0·86, 0·99, P=0·03) Se intakes were associated with a decreased digestive cancer risk. Statistically significant interactions were observed between dietary and total Se intakes and alcohol consumption as well as between total vitamin E intake and smoking status. This prospective cohort study with quantitative assessment of supplemental intakes suggests a potential protective effect of several antioxidants (vitamins C and E and Se) on digestive cancer risk, and a modulation of some of these relationships by alcohol consumption and smoking status.

Immunomodulatory basis of antioxidant therapy and its future prospects: an appraisal

Antioxidants are agents which can modulate oxidant-antioxidant profile of body system by neutralizing pro-oxidant molecules. The current scientific knowledge on mechanisms of antioxidant activity of biomolecules was critically reviewed with a special emphasis on immunomodulation. The immuno-oxidative wreckage of animals in various disease conditions and the role of biomodulators in curbing the oxidative stress through immune pathways were analyzed. The critical role of immunomodulatory mechanisms in controlling oxidative damage was identified. Selection of antioxidant therapy considering the immunopharmacology of the drug as well as immunological basis of disease may reduce treatment failure and adverse health effects. Hence, it is suggested that future studies on antioxidants may focus on the immuno-oxidative pathobiology to better understand its clinical effects and effective disease management.

Dietary polyacetylenes, falcarinol and falcarindiol, isolated from carrots prevents the formation of neoplastic lesions in the colon of azoxymethane-induced rats

Falcarinol (FaOH) and falcarindiol (FaDOH) are found in many food plants of the Apiaceae family. Carrots are a major dietary source of these polyacetylenes. Feeding azoxymethane (AOM)-induced rats with carrots and purified FaOH have previously been shown to inhibit neoplastic transformations in the colon. FaOH and FaDOH have also shown to have a synergistic effect in vitro, resulting in a significant increased cytotoxic activity. Based on these findings the antineoplastic effect of FaOH and FaDOH (purity > 99%) was investigated in the AOM-induced rat model. Twenty rats received rat diet containing 7 μg FaOH per g feed and 7 μg FaDOH per g feed and 20 rats were controls receiving only rat diet. Then carcinogenesis was induced in all 40 rats with the carcinogen AOM. All animals received the designated diet for 2 weeks before AOM induction and continued on the designated diet throughout the experiment. Rats were euthanized 18 weeks after the first AOM injection and macroscopic polyp/cancers were measured, harvested and stained for histology. The difference in sizes of aberrant crypt foci (ACF) were analysed in a Wilcoxon rank sum test, in which the median number of small ACF was 218 in controls and 145 in polyacetylene treated rats (P < 0.001). Fifteen control rats and 8 treated rats had macroscopic tumors (P = 0.027). The number of tumors larger than 3 mm were 6 and 1 in control and treated rats, respectively (P = 0.032). In conclusion dietary supplements with FaOH and FaDOH reduced the number of neoplastic lesions as well as the growth rate of the polyps suggesting a preventive effect of FaOH and FaDOH on the development of colorectal cancer.

Terpenoids as anti-colon cancer agents - A comprehensive review on its mechanistic perspectives

Multistep model of colon carcinogenesis has provided the framework to advance our understanding of the molecular basis of colon cancer. This multistage process of carcinogenesis takes a long period to transform from a normal epithelial cell to invasive carcinoma. Thus, it provides enough time to intervene the process of carcinogenesis especially through dietary modification. In spite of the in-depth understanding of the colon cancer etiology and pathophysiology and its association with diet, colon cancer remains a major cause of cancer mortality worldwide. Phytochemicals and their derivatives are gaining attention in cancer prevention and treatment strategies because of cancer chemotherapy associated adverse effects. Being the largest group of phytochemicals traditionally used for medicinal purpose in India and China, terpenoids are recently being explored as anticancer agents. Anticancer properties of terpenoids are associated with various mechanisms like counteraction of oxidative stress, potentiating endogenous antioxidants, improving detoxification potential, disrupting cell survival pathways and inducing apoptosis. This review gives a comprehensive idea of naturally occurring terpenoids as useful agents for the prevention of colon cancer with reference to their classes, sources and molecular targets. Based on the explored molecular targets further research in colon cancer chemoprevention is warranted.

Oxidative stress in prostate cancer patients: A systematic review of case control studies

BACKGROUND

Prostate cancer (PCa) is the most common cancer in men in Western countries. In-vitro and in-vivo studies suggest that oxidative stress (OS) and antioxidants play a key role in the pathogenesis of chronic diseases including PCa, which is promoted by the production of reactive oxygen species and impaired antioxidant defense mechanisms. This study evaluates the association between OS and men with PCa.

METHODS

A literature search was carried out on Medline, PubMed, and ScienceDirect databases, as well as manual searches from inception up to August 2015 using the keywords "Oxidative stress" or "Reactive oxygen species" or "Lipid peroxidation" AND "Prostate cancer." All studies including data on the measurement of OS biomarkers in PCa were included.

RESULTS

Twenty-three case control studies were retrieved with sample sizes ranging from 15 to 3,613 (6,439 participants in total). Markers of OS were significantly higher in patients with PCa compared with control groups in 21 studies. Two self-controlled case studies comparing OS between PCa cells and non-PCa cells in tissue biopsies found OS to be statistically higher in PCa cancer cells. Results on markers of antioxidant capacity (superoxide dismutase, catalase, glutathione, glutathione reductase, glutathione peroxidase, uric acid, lutein, lycopene, beta carotein, vitamin A, vitamin C, vitamin E, and total antioxidants) were not completely consistent in their association with PCa.

CONCLUSIONS

Upregulated OS profiles and impairment of antioxidant defense systems may play a role in men with PCa. To confirm these findings, robust clinical trials utilizing a personalized approach which monitors both OS and antioxidant markers during therapy are warranted.

Natural Products for Cancer Prevention: Clinical Update 2016

OBJECTIVES

To present a clinical update of natural products for cancer prevention and provide oncology nurses with an evidence-based review of natural products for patient counseling and education.

DATA SOURCES

Clinical trials published in PubMed.

CONCLUSION

In the past 4 years since the publication of the original review there have been minimal changes in the conclusions of the published literature on the use of natural products for cancer prevention. To date, clinical trials have not demonstrated conclusive benefit of using natural products for cancer prevention, and current guidelines do not recommend their use. This review provides an update on published and ongoing trials and can serve as an updated resource for nurses. Evidence-based natural products databases can help nurses stay current with the scientific literature and be effective educators and health coaches for their patients, who can be influenced by marketing of unregulated products.

IMPLICATIONS FOR NURSING PRACTICE

Patients often discuss the use of natural products with nurses. Nurses have an opportunity to educate and coach patients in effective preventive lifestyle practices.

Paleolithic and Mediterranean Diet Pattern Scores Are Inversely Associated with Biomarkers of Inflammation and Oxidative Balance in Adults

BACKGROUND

Chronic inflammation and oxidative balance are associated with poor diet quality and risk of cancer and other chronic diseases. A diet-inflammation/oxidative balance association may relate to evolutionary discordance.

OBJECTIVE

We investigated associations between 2 diet pattern scores, the Paleolithic and the Mediterranean, and circulating concentrations of 2 related biomarkers, high-sensitivity C-reactive protein (hsCRP), an acute inflammatory protein, and F2-isoprostane, a reliable marker of in vivo lipid peroxidation.

METHODS

In a pooled cross-sectional study of 30- to 74-y-old men and women in an elective outpatient colonoscopy population (n = 646), we created diet scores from responses on Willett food-frequency questionnaires and measured plasma hsCRP and F2-isoprostane concentrations by ELISA and gas chromatography-mass spectrometry, respectively. Both diet scores were calculated and categorized into quintiles, and their associations with biomarker concentrations were estimated with the use of general linear models to calculate and compare adjusted geometric means, and via unconditional ordinal logistic regression.

RESULTS

There were statistically significant trends for decreasing geometric mean plasma hsCRP and F2-isoprostane concentrations with increasing quintiles of the Paleolithic and Mediterranean diet scores. The multivariable-adjusted ORs comparing those in the highest with those in the lowest quintiles of the Paleolithic and Mediterranean diet scores were 0.61 (95% CI: 0.36, 1.05; P-trend = 0.06) and 0.71 (95% CI: 0.42, 1.20; P-trend = 0.01), respectively, for a higher hsCRP concentration, and 0.51 (95% CI: 0.27, 0.95; P-trend 0.01) and 0.39 (95% CI: 0.21, 0.73; P-trend = 0.01), respectively, for a higher F2-isoprostane concentration.

CONCLUSION

These findings suggest that diets that are more Paleolithic- or Mediterranean-like may be associated with lower levels of systemic inflammation and oxidative stress in humans.

Antioxidant strategies in respiratory medicine

Pulmonary oxidant stress plays an important pathogenetic role in disease conditions including acute lung injury/adult respiratory distress syndrome (ALI/ARDS), hyperoxia, ischemia-reperfusion, sepsis, radiation injury, lung transplantation, COPD, and inflammation. Reactive oxygen species (ROS), released from activated macrophages and leukocytes or formed in the pulmonary epithelial and endothelial cells, damage the lungs and initiate cascades of pro-inflammatory reactions propagating pulmonary and systemic stress. Diverse molecules including small organic compounds (e.g. gluthatione, tocopherol (vitamin E), flavonoids) serve as natural antioxidants that reduce oxidized cellular components, decompose ROS and detoxify toxic oxidation products. Antioxidant enzymes can either facilitate these antioxidant reactions (e.g. peroxidases using glutathione as a reducing agent) or directly decompose ROS (e.g. superoxide dismutases [SOD] and catalase). Many antioxidant agents are being tested for treatment of pulmonary oxidant stress. The administration of small antioxidants via the oral, intratracheal and vascular routes for the treatment of short- and long-term oxidant stress showed rather modest protective effects in animal and human studies. Intratracheal and intravascular administration of antioxidant enzymes are being currently tested for the treatment of acute oxidant stress. For example, intratracheal administration of recombinant human SOD is protective in premature infants exposed to hyperoxia. However, animal and human studies show that more effective delivery of drugs to cells experiencing oxidant stress is needed to improve protection. Diverse delivery systems for antioxidants including liposomes, chemical modifications (e.g. attachment of masking pegylated [PEG]-groups) and coupling to affinity carriers (e.g. antibodies against cellular adhesion molecules) are being employed and currently tested, mostly in animal and, to a limited extent, in humans, for the treatment of oxidant stress. Further studies are needed, however, in order to develop and establish effective applications of pulmonary antioxidant interventions useful in clinical practice. Although beyond the scope of this review, antioxidant gene therapies may eventually provide a strategy for the management of subacute and chronic pulmonary oxidant stress.

Nutrients, foods, and colorectal cancer prevention

Diet has an important role in the development of colorectal cancer. In the past few decades, findings from extensive epidemiologic and experimental investigations have linked consumption of several foods and nutrients to the risk of colorectal neoplasia. Calcium, fiber, milk, and whole grains have been associated with a lower risk of colorectal cancer, and red meat and processed meat have been associated with an increased risk. There is substantial evidence for the potential chemopreventive effects of vitamin D, folate, fruits, and vegetables. Nutrients and foods also may interact, as a dietary pattern, to influence colorectal cancer risk. Diet likely influences colorectal carcinogenesis through several interacting mechanisms. These include the direct effects on immune responsiveness and inflammation, and the indirect effects of overnutrition and obesity-risk factors for colorectal cancer. Emerging evidence also implicates the gut microbiota as an important effector in the relationship between diet and cancer. Dietary modification therefore has the promise of reducing colorectal cancer incidence.

Inhibitory effects of astaxanthin on azoxymethane-induced colonic preneoplastic lesions in C57/BL/KsJ-db/db mice

Background

Obesity and related metabolic abnormalities, including excess oxidative stress and chronic inflammation, are associated with colorectal carcinogenesis. Astaxanthin, a xanthophyll carotenoid found in aquatic animals, is known to possess antioxidant, anti-inflammatory, and antineoplastic properties. The present study examined the effects of astaxanthin on the development of azoxymethane (AOM)-induced colonic premalignant lesions in C57BL/KsJ-db/db (db/db) obese mice.

Method

Male db/db mice were administered 4 weekly subcutaneous injections of AOM (15 mg/kg body weight) from 5 weeks of age and subsequently, from 1 week after the last injection of AOM, were fed a diet containing 200 ppm astaxanthin throughout the experiment (8 weeks).

Result

The development of colonic premalignant lesions, i.e., aberrant crypt foci and β-catenin accumulated crypts, was significantly inhibited in mice treated with astaxanthin than in mice fed the basal diet. Astaxanthin administration markedly reduced urinary levels of 8-OHdG and serum levels of d-ROMs, which are oxidative stress markers, while increasing the expression of mRNA for the antioxidant enzymes GPx1, SOD1, and CAT in the colonic mucosa of AOM-treated db/db mice. The expression levels of IL-1β, IL-6, F4/80, CCL2, and CXCL2 mRNA in the colonic mucosa of AOM-treated mice were significantly decreased by astaxanthin. Dietary feeding with astaxanthin also resulted in a reduction in the numbers of NF-κB- and PCNA-positive cells that were increased by AOM exposure, in the colonic epithelium.

Conclusion

These findings suggest that astaxanthin inhibits the development of colonic premalignant lesions in an obesity-related colorectal carcinogenesis model by reducing oxidative stress, attenuating chronic inflammation, and inhibiting NF-κB activation and cell proliferation in the colonic mucosa. Astaxanthin, therefore, may be a potential candidate as a chemoprevention agent against colorectal carcinogenesis in obese individuals.

Vitamin E and C supplementation and risk of cancer in men: posttrial follow-up in the Physicians' Health Study II randomized trial

BACKGROUND

Recent posttrial analysis of a completed randomized trial found an increased risk of prostate cancer among healthy men taking high-dose vitamin E supplements. Trials that examined the effect of vitamin C supplements on cancer risk are few.

OBJECTIVE

We examined whether vitamin E or vitamin C supplementation affects the risk of cancer events during posttrial follow-up of the Physicians' Health Study II.

DESIGN

Beginning in 1997, a total of 14,641 US male physicians aged ≥50 y were randomly assigned to receive 400 IU of vitamin E every other day, 500 mg of vitamin C daily, or their respective placebos. The vitamin E and vitamin C treatment ended in 2007, and observational follow-up continued through June 2011.

RESULTS

This study included an additional 356 cases of incident prostate cancer and 771 total cancers that developed during a mean (maximum) of 2.8 (3.8) y of posttrial observation. During an overall mean of 10.3 (13.8) y, there were a total of 1373 incident prostate cancers and 2669 total cancers documented. In comparison with placebo, vitamin E supplementation had no effect on the incidence of prostate cancer (HR: 0.99; 95% CI: 0.89, 1.10) or total cancers (HR: 1.02; 95% CI: 0.95, 1.10). There was also no effect of vitamin C supplementation on total cancers (HR: 1.02; 95% CI: 0.94, 1.10) or incident prostate cancer (HR: 1.03; 95% CI: 0.93, 1.15). Neither vitamin E nor vitamin C supplementation had effects on other site-specific cancers overall. Stratification by known cancer risk factors, history of cancer, other randomized treatment, and follow-up time showed no significant interactions.

CONCLUSION

In this large-scale randomized trial in men, vitamin E and C supplementation had no immediate or long-term effects on the risk of total cancers, prostate cancer, or other site-specific cancers.

Nutraceuticals for older people: facts, fictions and gaps in knowledge

In the last decades nutraceuticals have entered the health market as an easy and attractive means of preventing diseases. These products are of interest for an increasingly health-concerned society and may be especially relevant for preventing or delaying a number of age-related diseases, i.e. arthritis, cancer, metabolic and cardiovascular diseases, osteoporosis, cataracts, brain disorders, etc. Nutraceuticals are marketed in a variety of forms, composition and potential applications which have made their definition ambiguous and their use uncontrolled and poorly funded. Although epidemiological, animal and in vitro studies have given evidence of the potential benefits of some of these nutraceuticals or of their components, definitive proof of their effects in appropriate human clinical trials is still lacking in most cases, more critically among people above 65 years of age. We cover the well-established nutraceuticals (polyvitamins, omega-3 fatty acids, etc.) and will focus on many other 'novel' commercial nutraceuticals where the scientific evidence is more limited (food extracts, polyphenols, carotenoids, etc.). Solid scientific evidence has been reported only for a few nutraceuticals, which have some health claims approved by the European Food Safety Authority (EFSA). Further well-designed trials are needed to improve the current knowledge on the health benefits of nutraceuticals in the elderly. Overall, there are some facts, a lot of fiction and many gaps in the knowledge of nutraceutical benefits.

Antioxidant supplement and long-term reduction of recurrent adenomas of the large bowel. A double-blind randomized trial

BACKGROUND

Patients who undergo polypectomy are at increased risk of adenoma recurrence. The preventive potential of vitamins (A, C and E) and selenium supplementation represent an interesting opportunity for colorectal cancer prevention.

METHODS

To assess the efficacy of a combination of these micronutrients in reducing the incidence of recurrent adenomas in subjects on post-polypectomy endoscopic follow-up, a double-blind placebo-controlled randomized trial was started in Italy in 1988. A total of 411 patients were randomized to receive either an active compound (200 μg selenium, 30 mg zinc, 2 mg vitamin A, 180 mg vitamin C, 30 mg vitamin E) or a placebo daily for 5 years. Of them, 330 had follow-up colonoscopy (164 in the intervention and 166 in the placebo group).

RESULTS

After a median follow-up of 4 years (range 1-15 years), 100 patients had recurrence: 38 in the intervention and 62 in the placebo arm. The 15-year cumulative incidence of recurrence was 48.3% in the intervention and 64.5% in the placebo arm (HR = 0.59; log-rank P = 0.009). A 39% reduction of the risk of recurrence was observed in the intervention compared to the placebo group (adjusted HR = 0.61; 95% CI 0.41-0.92): the risk reduction was similar for small tubular (adjusted HR = 0.61; 95% CI 0.37-0.99) and advanced adenomas (adjusted HR = 0.50; 95% CI 0.24-1.01).

CONCLUSIONS

Our study showed a statistically significant effect of antioxidant supplementation on adenoma recurrence. Further clinical trials are needed to address the role of antioxidants in subgroups of subjects at increased risk for colorectal cancer.

Dietary administration of δ- and γ-tocopherol inhibits tumorigenesis in the animal model of estrogen receptor-positive, but not HER-2 breast cancer

Tocopherol, a member of the vitamin E family, consists of four forms designated as α, β, γ, and δ. Several large cancer prevention studies with α-tocopherol have reported no beneficial results, but recent laboratory studies have suggested that δ- and γ-tocopherol may be more effective. In two different animal models of breast cancer, the chemopreventive activities of individual tocopherols were assessed using diets containing 0.3% of tocopherol (α-, δ-, or γ-) or 0.3% of a γ-tocopherol rich mixture (γ-TmT). Although administration of tocopherols did not prevent human epidermal growth factor receptor 2 (HER2/neu)-driven tumorigenesis, δ- and γ-tocopherols inhibited hormone-dependent mammary tumorigenesis in N-methyl-N-nitrosourea (NMU)-treated female Sprague-Dawley rats. NMU-treated rats showed an average tumor burden of 10.6 ± 0.8 g in the control group at 11 weeks, whereas dietary administration of δ- and γ-tocopherols significantly decreased tumor burden to 7.2 ± 0.8 g (P < 0.01) and 7.1 ± 0.7 g (P < 0.01), respectively. Tumor multiplicity was also reduced in δ- and γ-tocopherol treatment groups by 42% (P < 0.001) and 32% (P < 0.01), respectively. In contrast, α-tocopherol did not decrease tumor burden or multiplicity. In mammary tumors, the protein levels of proapoptotic markers (BAX, cleaved caspase-9, cleaved caspase-3, cleaved PARP) were increased, whereas antiapoptotic markers (Bcl-2, XIAP) were inhibited by δ-tocopherol, γ-tocopherol, and γ-TmT. Furthermore, markers of cell proliferation (PCNA, PKCα), survival (PPAR-γ, PTEN, phospho-Akt), and cell cycle (p53, p21) were affected by δ- and γ-tocopherols. Both δ- and γ-tocopherols, but not α-tocopherol, seem to be promising agents for the prevention of hormone-dependent breast cancer.

Leukocyte DNA methylation and colorectal cancer among male smokers

AIM: To explore the association between methylation in leukocyte DNA and colorectal cancer (CRC) risk in male smokers using the α-tocopherol, β-carotene cancer prevention study.

METHODS: About 221 incident CRC cases, and 219 controls, frequency-matched on age and smoking intensity were included. DNA methylation of 1505 CpG sites selected from 807 genes were evaluated using Illumina GoldenGate Methylation Cancer Panel I in pre-diagnostic blood leukocytes of study subjects. Tertiles of methylation level classified according to the distribution in controls for each CpG site were used to analyze the association between methylation level and CRC risk with logistic regression. The time between blood draw to cancer diagnosis (classifying cases according to latency) was incorporated in further analyses using proportional odds regression.

RESULTS: We found that methylation changes of 31 CpG sites were associated with CRC risk at P < 0.01 level. Though none of these 31 sites remained statistically significant after Bonferroni correction, the most statistically significant CpG site associated with CRC risk achieved a P value of 1.0 × 10^-4. The CpG site is located in DSP gene, and the risk estimate was 1.52 (95% CI: 0.91-2.53) and 2.62 (95% CI: 1.65-4.17) for the second and third tertile comparing with the lowest tertile respectively. Taking the latency information into account strengthened some associations, suggesting that the methylation levels of corresponding sites might change over time with tumor progression.

CONCLUSION: The results suggest that the methylation level of some genes were associated with cancer susceptibility and some were related to tumor development over time. Further studies are warranted to confirm and refine our results.

Dietary intakes of retinol, carotenes, vitamin C, and vitamin E and colorectal cancer risk: the Fukuoka colorectal cancer study

It has long been a matter of interest whether antioxidant vitamins are protective against colorectal cancer as well as human cancers in general, but epidemiological evidence is inconclusive. We investigated associations of dietary intakes of retinol and antioxidant vitamins with colorectal cancer risk in 816 incident cases of histologically confirmed colorectal cancer and 815 controls randomly selected for the Fukuoka colorectal cancer study in Japan. Dietary intakes were assessed by a PC-assisted interview regarding 148 food items. Statistical adjustment was made for body mass index, physical activity, calcium, and n-3 fatty acid intake and other factors. Retinol intake was significantly, inversely associated with colorectal cancer risk; the odds ratio for the highest vs. lowest was 0.55 (95% CI: 0.35, 0.88; P (trend) = 0.01) in women, but a modest increase in the risk was observed among men with the highest intake of retinol. Liver was the major source of retinol intake and showed similar associations with colorectal cancer risk in men and women. Intake of carotenes, vitamin C, and vitamin E were not related to colorectal cancer risk in either men or women. The study did not support a hypothesis that dietary intake of antioxidant vitamins is protective in the development of colorectal cancer.

Natural products for cancer prevention

OBJECTIVES

To review the clinical trial literature on the use and effects of natural products for cancer prevention.

DATA SOURCES

Clinical trials published in PubMed.

CONCLUSION

There is a growing body of literature on the use of natural products for cancer prevention. To date, few trials have demonstrated conclusive benefit. Current guidelines recommend against the use of natural products for cancer prevention.

IMPLICATIONS FOR NURSING PRACTICE

Clinicians should ask patients about their use of natural products and motivations for use. If patients are using natural products for cancer prevention, they should be counseled on the current guidelines, as well as their options for other cancer prevention strategies.

Genome-wide association study identifies three common variants associated with serologic response to vitamin E supplementation in men

Vitamin E inhibits lipid peroxidation in cell membranes, prevents oxidative damage to DNA by scavenging free radicals, and reduces carcinogen production. No study to our knowledge, however, has examined the association between genetic variants and response to long-term vitamin E supplementation. We conducted a genome-wide association study (GWAS) of common variants associated with circulating α-tocopherol concentrations following 3 y of controlled supplementation. The study population included 2112 middle-aged, male smokers in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study cohort who received a trial supplementation of α-tocopherol (50 mg/d) and had fasting serum α-tocopherol concentrations measured after 3 y. Serum concentrations were log-transformed for statistical analysis and general linear models adjusted for age, BMI, serum total cholesterol, and cancer case status. Associations with serum response to α-tocopherol supplementation achieved genome-wide significance for 2 single nucleotide polymorphisms (SNP): rs964184 on 11q23.3 (P = 2.6 × 10(-12)) and rs2108622 on 19pter-p13.11 (P = 2.2 × 10(-7)), and approached genome-wide significance for one SNP, rs7834588 on 8q12.3 (P = 6.2 × 10(-7)). Combined, these SNP explain 3.4% of the residual variance in serum α-tocopherol concentrations during controlled vitamin E supplementation. A GWAS has identified 3 genetic variants at different loci that appear associated with serum concentrations after vitamin E supplementation in men. Identifying genetic variants that influence serum nutrient biochemical status (e.g., α-tocopherol) under supplementation conditions improves our understanding of the biological determinants of these nutritional exposures and their associations with cancer etiology.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Our systematic review has demonstrated that antioxidant supplements may increase mortality. We have now updated this review.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements for prevention of mortality in adults.

SEARCH METHODS

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index Expanded, and Conference Proceedings Citation Index-Science to February 2011. We scanned bibliographies of relevant publications and asked pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention.

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Random-effects and fixed-effect model meta-analyses were conducted. Risk of bias was considered in order to minimise the risk of systematic errors. Trial sequential analyses were conducted to minimise the risk of random errors. Random-effects model meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Seventy-eight randomised trials with 296,707 participants were included. Fifty-six trials including 244,056 participants had low risk of bias. Twenty-six trials included 215,900 healthy participants. Fifty-two trials included 80,807 participants with various diseases in a stable phase. The mean age was 63 years (range 18 to 103 years). The mean proportion of women was 46%. Of the 78 trials, 46 used the parallel-group design, 30 the factorial design, and 2 the cross-over design. All antioxidants were administered orally, either alone or in combination with vitamins, minerals, or other interventions. The duration of supplementation varied from 28 days to 12 years (mean duration 3 years; median duration 2 years). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects model meta-analysis (21,484 dead/183,749 (11.7%) versus 11,479 dead/112,958 (10.2%); 78 trials, relative risk (RR) 1.02, 95% confidence interval (CI) 0.98 to 1.05) but significantly increased mortality in a fixed-effect model (RR 1.03, 95% CI 1.01 to 1.05). Heterogeneity was low with an I(2)- of 12%. In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. Meta-regression analysis did not find a significant difference in the estimated intervention effect in the primary prevention and the secondary prevention trials. In the 56 trials with a low risk of bias, the antioxidant supplements significantly increased mortality (18,833 dead/146,320 (12.9%) versus 10,320 dead/97,736 (10.6%); RR 1.04, 95% CI 1.01 to 1.07). This effect was confirmed by trial sequential analysis. Excluding factorial trials with potential confounding showed that 38 trials with low risk of bias demonstrated a significant increase in mortality (2822 dead/26,903 (10.5%) versus 2473 dead/26,052 (9.5%); RR 1.10, 95% CI 1.05 to 1.15). In trials with low risk of bias, beta-carotene (13,202 dead/96,003 (13.8%) versus 8556 dead/77,003 (11.1%); 26 trials, RR 1.05, 95% CI 1.01 to 1.09) and vitamin E (11,689 dead/97,523 (12.0%) versus 7561 dead/73,721 (10.3%); 46 trials, RR 1.03, 95% CI 1.00 to 1.05) significantly increased mortality, whereas vitamin A (3444 dead/24,596 (14.0%) versus 2249 dead/16,548 (13.6%); 12 trials, RR 1.07, 95% CI 0.97 to 1.18), vitamin C (3637 dead/36,659 (9.9%) versus 2717 dead/29,283 (9.3%); 29 trials, RR 1.02, 95% CI 0.98 to 1.07), and selenium (2670 dead/39,779 (6.7%) versus 1468 dead/22,961 (6.4%); 17 trials, RR 0.97, 95% CI 0.91 to 1.03) did not significantly affect mortality. In univariate meta-regression analysis, the dose of vitamin A was significantly associated with increased mortality (RR 1.0006, 95% CI 1.0002 to 1.001, P = 0.002).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.

Chemopreventive activity of vitamin E in breast cancer: a focus on γ- and δ-tocopherol

Vitamin E consists of eight different variants: α-, β-, γ-, and δ-tocopherols (saturated phytyl tail) and α-, β-, γ-, and δ-tocotrienols (unsaturated phytyl tail). Cancer prevention studies with vitamin E have primarily utilized the variant α-tocopherol. To no avail, a majority of these studies focused on variant α-tocopherol with inconsistent results. However, γ-tocopherol, and more recently δ-tocopherol, have shown greater ability to reduce inflammation, cell proliferation, and tumor burden. Recent results have shown that γ-enriched mixed tocopherols inhibit the development of mammary hyperplasia and tumorigenesis in animal models. In this review, we discuss the possible differences between the variant forms, molecular targets, and cancer-preventive effects of tocopherols. We recommend that a γ-enriched mixture, γ- and δ-tocopherol, but not α-tocopherol, are promising agents for breast cancer prevention and warrant further investigation.

Clinical trials of antioxidants as cancer prevention agents: past, present, and future

The purpose of this review is to summarize the most important human clinical trials of antioxidants as cancer prevention agents conducted to date, provide an overview of currently ongoing studies, and discuss future steps needed to advance research in this field. To date there have been several large (at least 7000 participants) trials testing the efficacy of antioxidant supplements in preventing cancer. The specific agents (diet-derived direct antioxidants and essential components of antioxidant enzymes) tested in those trials included β-carotene, vitamin E, vitamin C, selenium, retinol, zinc, riboflavin, and molybdenum. None of the completed trials produced convincing evidence to justify the use of traditional antioxidant-related vitamins or minerals for cancer prevention. Our search of ongoing trials identified six projects at various stages of completion. Five of those six trials use selenium as the intervention of interest delivered either alone or in combination with other agents. The lack of success to date can be explained by a variety of factors that need to be considered in the next generation research. These factors include lack of good biological rationale for selecting specific agents of interest; limited number of agents tested to date; use of pharmacological, rather than dietary, doses; and insufficient duration of intervention and follow-up. The latter consideration underscores the need for alternative endpoints that are associated with increased risk of neoplasia (i.e., biomarkers of risk), but are detectable prior to tumor occurrence. Although dietary antioxidants are a large and diverse group of compounds, only a small proportion of candidate agents have been tested. In summary, the strategy of focusing on large high-budget studies using cancer incidence as the endpoint and testing a relatively limited number of antioxidant agents has been largely unsuccessful. This lack of success in previous trials should not preclude us from seeking novel ways of preventing cancer by modulating oxidative balance. On the contrary, the well demonstrated mechanistic link between excessive oxidative stress and carcinogenesis underscores the need for new studies. It appears that future large-scale projects should be preceded by smaller, shorter, less expensive biomarker-based studies that can serve as a link from mechanistic and observational research to human cancer prevention trials. These relatively inexpensive studies would provide human experimental evidence for the likely efficacy, optimum dose, and long-term safety of the intervention of interest that would then guide the design of safe, more definitive large-scale trials.

Serum vitamin E concentrations among highly functioning hip fracture patients are higher than in nonfracture controls

Malnutrition after hip fracture is common and associated with poor outcomes and protracted recovery. Low concentrations of vitamin E have been associated with incident decline in physical function among older adults and may, therefore, be particularly important to functionally compromised patients hip fracture patients. Serum concentrations of α-tocopherol and γ-tocopherol, the 2 major forms of vitamin E, were assessed in 148 female hip fracture patients 65 years or older from the Baltimore Hip Studies cohort 4 around the time of fracture (baseline) and at 2, 6, and 12 month postfracture follow-up visits (recovery). It was hypothesized that mean concentrations of both forms of vitamin E among these hip fracture patients would be lowest at the baseline visit and increase at each study visit during the year after fracture. Linear regression and generalized estimating equations were used to assess changes in vitamin E concentrations after adjustment for covariates and to determine predictors of vitamin E concentrations at baseline and throughout recovery. It was also hypothesized that vitamin E concentrations shortly after hip fracture would be lower than those in nonfracture controls after adjustment for covariates. To evaluate this hypothesis, linear regression was used to perform adjusted comparisons of baseline vitamin E concentrations among Baltimore Hip Studies cohort 4 participants to 1076 older women without history of hip fracture from the Women's Health and Aging Study I, Invecchiare in Chianti Study, and the National Health and Nutrition Examination Surveys. Mean α-tocopherol was lowest at baseline, and time from fracture to blood draw was positively associated with baseline α-tocopherol (P = .005). Mean γ-tocopherol did not change appreciably throughout the year after fracture, although it fluctuated widely within individuals. Serum concentrations of α-tocopherol and γ-tocopherol were highest among the hip fracture population after adjustment (P < .0001). In general, highly cognitively and physically functioning hip fracture patients demonstrated higher vitamin E concentrations. Thus, the relatively high degree of function among this cohort of hip fracture patients may explain their higher-than-expected vitamin E concentrations.

Colorectal cancer: what should patients and families be told to lower the risk of colorectal cancer?

Colorectal cancer (CRC) is the second most common cause of cancer-related death in the United States. CRC, however, is potentially preventable, and several strategies may be employed to decrease the incidence of and mortality from CRC. Understanding of individual risk and adherence to screening and surveillance recommendations undoubtedly will reduce CRC-associated deaths. Several natural and synthetic chemopreventive agents may prove effective for both primary and secondary CRC chemoprevention. Finally, dietary modifications (ie, increased dietary fiber, fruits and vegetables, and decreased red meat) and other lifestyle changes (i.e., increased physical activity, weight maintenance, avoidance of smoking, and moderation of alcohol intake) also may lower the risk of developing CRC.

Cancer-preventive activities of tocopherols and tocotrienols

The cancer-preventive activity of vitamin E has been studied. Whereas some epidemiological studies have suggested a protective effect of vitamin E against cancer formation, many large-scale intervention studies with alpha-tocopherol (usually large doses) have not demonstrated a cancer-preventive effect. Studies on alpha-tocopherol in animal models also have not demonstrated robust cancer prevention effects. One possible explanation for the lack of demonstrable cancer-preventive effects is that high doses of alpha-tocopherol decrease the blood and tissue levels of delta-tocopherols. It has been suggested that gamma-tocopherol, due to its strong anti-inflammatory and other activities, may be the more effective form of vitamin E in cancer prevention. Our recent results have demonstrated that a gamma-tocopherol-rich mixture of tocopherols inhibits colon, prostate, mammary and lung tumorigenesis in animal models, suggesting that this mixture may have a high potential for applications in the prevention of human cancer. In this review, we discuss biochemical properties of tocopherols, results of possible cancer-preventive effects in humans and animal models and possible mechanisms involved in the inhibition of carcinogenesis. Based on this information, we propose that a gamma-tocopherol-rich mixture of tocopherols is a very promising cancer-preventive agent and warrants extensive future research.

Lipid peroxidation and etheno DNA adducts in white blood cells of liver fluke-infected patients: protection by plasma alpha-tocopherol and praziquantel

Chronic infection by the liver fluke Opisthorchis viverrini is a strong risk factor for cholangiocarcinoma. To clarify the involvement of oxidative stress and lipid peroxidation-derived DNA damage, etheno (epsilon)-DNA adducts (epsilondA, epsilondC) in WBC and plasma alpha-tocopherol were measured in samples collected from O. viverrini-infected Thai patients (n = 50) and healthy noninfected volunteers (n = 20). epsilondA and epsilondC levels were three to five times higher (P < 0.001) in infected patients than in controls; O. viverrini infection also increased two to three times in the plasma inflammatory indicators, 8-isoprostane, malondialdehyde, and nitrate/nitrite. Mean plasma alpha-tocopherol levels were two times lower in patients than in healthy controls (P < 0.001). Two months after a single dose to infected patients of the antiparasitic drug praziquantel, epsilondA and epsilondC levels in WBC were decreased to control level (P < 0.03); plasma 8-isoprostane, malondialdehyde, nitrate/nitrite, and alkaline phosphatase (ALP) were concomitantly lowered. epsilondA and epsilondC levels in WBC were positively correlated with plasma 8-isoprostane, malondialdehyde, and nitrate/nitrite levels and ALP activity, whereas plasma alpha-tocopherol levels showed inverse correlations. We conclude that chronic O.viverrini infection induces an accumulation of lipid peroxidation-derived DNA damage through oxidative/nitrative stress, which is lowered by the plasma alpha-tocopherol and by antiparasitic drug therapy. Etheno adducts in WBC and urine should be explored as a risk marker for opisthorchiasis-related cholangiocarcinoma, and to assess the efficacy of preventive and therapeutic interventions.

Beta-carotene affects oxidative stress-related DNA damage in lung epithelial cells and in ferret lung

Beta-carotene (BC) was found to enhance lung cancer risk in smokers. This adverse effect was unexpected because BC was thought to act as an anti-oxidant against cigarette smoke-derived radicals. These radicals can directly or indirectly damage DNA, leading to the formation of pro-mutagenic DNA lesions such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) and 3-(2-deoxy-beta-D-erythro-pentafuranosyl)pyrimido[1,2-alpha]purin-10(3H)-one deoxyguanosine (M(1)dG). Later, it was suggested that high concentrations of BC could also result in pro-oxidant effects. Therefore, we investigated whether high but physiologically feasible concentrations of BC were able to alter (i) the formation of radicals in vitro assessed by electron spin resonance spectroscopy, (ii) the levels of 8-oxo-dG and M(1)dG in vitro in lung epithelial cells after incubation with hydrogen peroxide (H(2)O(2)) and the smoke-derived carcinogen benzo[a]pyrene (B[a]P) and (iii) the levels of 8-oxo-dG and M(1)dG in vivo in ferrets' lung after chronic exposure to B[a]P. BC increased in vitro hydroxyl radical formation in the Fenton reaction but inhibited the formation of carbon-centered radicals. Similarly, BC was able to enhance 8-oxo-dG in vitro in lung epithelial cells. On the other hand, BC significantly inhibited M(1)dG formation in lung epithelial cells, especially after induction of M(1)dG by H(2)O(2) or B[a]P. Finally, BC supplementation of ferrets also resulted in a significant decrease in M(1)dG, but in contrast to the in vitro experiments, no effect was observed on 8-oxo-dG levels, probably because of increased base excision repair capacities as assessed by a modified comet assay. These data indicate that the fate of BC being a pro- or anti-oxidant strongly depends on the type of radical involved.

Effects of antioxidant supplements on cancer prevention: meta-analysis of randomized controlled trials

BACKGROUND

This meta-analysis aimed to investigate the effect of antioxidant supplements on the primary and secondary prevention of cancer as reported by randomized controlled trials.

METHODS

We searched Medline (PubMed), Excerpta Medica database, and the Cochrane Review in October 2007.

RESULTS

Among 3327 articles searched, 31 articles on 22 randomized controlled trials, which included 161 045 total subjects, 88 610 in antioxidant supplement groups and 72 435 in placebo or no-intervention groups, were included in the final analyses. In a fixed-effects meta-analysis of all 22 trials, antioxidant supplements were found to have no preventive effect on cancer [relative risk (RR) 0.99; 95% confidence interval (CI) 0.96-1.03). Similar findings were observed in 12 studies on primary prevention trials (RR 1.00; 95% CI 0.97-1.04) and in nine studies on secondary prevention trials (RR 0.97; 95% CI 0.83-1.13). Further, subgroup analyses revealed no preventive effect on cancer according to type of antioxidant, type of cancer, or the methodological quality of the studies. On the other hand, the use of antioxidant supplements significantly increased the risk of bladder cancer (RR 1.52; 95% CI 1.06-2.17) in a subgroup meta-analysis of four trials.

CONCLUSIONS

The meta-analysis of randomized controlled trials indicated that there is no clinical evidence to support an overall primary and secondary preventive effect of antioxidant supplements on cancer. The effects of antioxidant supplements on human health, particularly in relation to cancer, should not be overemphasized because the use of those might be harmful for some cancer.

Smoking attenuates the negative association between carotenoids consumption and colorectal cancer risk

OBJECTIVES

Consumption of vegetables and fruits, physical activity, obesity and caloric intake are all strongly related to the risk of colorectal cancer (CRC). The association between dietary intake of carotenoids from vegetables/fruits and risk of CRC in the context of cigarette smoking was studied in a nutritionally diverse population.

METHODS

The study included 1,817 age sex residence-matched case-control pairs from a population-based study in Northern Israel. Data were acquired by food-frequency questionnaire. Individual intake of carotenoid isomers was calculated using an Israeli food content database. Odds ratios (ORs) were calculated using conditional logistic regression models adjusted for known risk factors.

RESULTS

Strong inverse associations were found with consumption of 9-cis-beta-carotene (OR = 0.35, 0.26-0.47), all-trans-beta-carotene (OR = 0.58, 0.44-0.76), cis-beta-cryptoxanthin (OR = 0.67, 0.50-0.90), all-trans-zeaxanthin (OR = 0.64, 0.48-0.86), and lutein (OR = 0.74, 0.57-0.96). Lycopene (OR = 2.22, 1.71-2.89) and all-trans-beta-cryptoxanthin (OR = 2.01, 1.48-2.73) were associated with increased risk of CRC. Inverse associations of most carotenoids with CRC, demonstrated in non-smokers, were much attenuated or reversed in past or current smokers with a highly significant interaction term.

CONCLUSIONS

Consumption of most dietary carotenoids was found to be strongly associated with reduced risk of CRC. However, smoking significantly attenuated or reversed this observed protective effect on CRC occurrence. Smokers should be advised that smoking also hampers the potential health promoting effects of high fruit and vegetable consumption.

Carotenoid intake and colorectal cancer risk: the multiethnic cohort study

Background

A protective effect of fruits and vegetables against colorectal cancer has been supported by many epidemiologic studies. This suggests that the carotenoids frequently found in these foods play a role in the prevention of this common cancer. To examine associations between the intake of individual and total carotenoids and the risk of colorectal cancer, we analyzed prospective data from the Multiethnic Cohort Study.

Methods

This analysis includes 85 898 men and 105 106 women who completed a quantitative food frequency questionnaire in 1993–1996. The participants were African Americans, Native Hawaiians, Japanese Americans, Latinos, and whites aged 45–75 years at cohort entry. After an average follow-up of 8.2 years, 1292 and 1086 incident cases of colorectal cancer were identified in men and women, respectively. Cox proportional hazard models were used to estimate relative risks of colorectal cancer.

Results

No significant associations were found between intake of individual and total carotenoids and colorectal cancer risk either in men or women, except for β-cryptoxanthin, which showed a mild protective effect in men. When the associations were investigated separately for colon and rectal cancer, lycopene intake was related to an increased risk of rectal cancer in men. A decreased risk was seen for total β-carotene in male current smokers, but the test for interaction with smoking status was not significant. No association was observed in each ethnic-sex group.

Conclusion

Overall, our findings do not support a significant association between carotenoid intake and colorectal cancer, although some associations were seen in subgroup analyses.

Beta-carotene metabolites enhance inflammation-induced oxidative DNA damage in lung epithelial cells

beta-Carotene (BC) intake has been shown to enhance lung cancer risk in smokers and asbestos-exposed subjects (according to the ATBC and CARET studies), but the mechanism behind this procarcinogenic effect of BC is unclear. Both smoking and asbestos exposure induce an influx of inflammatory neutrophils into the airways, which results in an increased production of reactive oxygen species and formation of promutagenic DNA lesions. Therefore, the aim of our study was to investigate the effects of BC and its metabolites (BCM) on neutrophil-induced genotoxicity. We observed that the BCM vitamin A (Vit A) and retinoic acid (RA) inhibited the H(2)O(2)-utilizing enzyme myeloperoxidase (MPO), which is released by neutrophils, thereby reducing H(2)O(2) conversion. Moreover, BC and BCM were able to increase (.)OH formation from H(2)O(2) in the Fenton reaction (determined by electron spin resonance spectroscopy). Addition of Vit A and RA to lung epithelial cells that were co-incubated with activated neutrophils resulted in a significant increase in the level of oxidized purines assessed by the formamidopyrimidine DNA glycosylase-modified comet assay. These data indicate that BCM can enhance neutrophil-induced genotoxicity by inhibition of MPO in combination with subsequent increased formation of hydroxyl radicals.

Vitamins E and C in the prevention of prostate and total cancer in men: the Physicians' Health Study II randomized controlled trial

CONTEXT

Many individuals take vitamins in the hopes of preventing chronic diseases such as cancer, and vitamins E and C are among the most common individual supplements. A large-scale randomized trial suggested that vitamin E may reduce risk of prostate cancer; however, few trials have been powered to address this relationship. No previous trial in men at usual risk has examined vitamin C alone in the prevention of cancer.

OBJECTIVE

To evaluate whether long-term vitamin E or C supplementation decreases risk of prostate and total cancer events among men.

DESIGN, SETTING, AND PARTICIPANTS

The Physicians' Health Study II is a randomized, double-blind, placebo-controlled factorial trial of vitamins E and C that began in 1997 and continued until its scheduled completion on August 31, 2007. A total of 14,641 male physicians in the United States initially aged 50 years or older, including 1307 men with a history of prior cancer at randomization, were enrolled.

INTERVENTION

Individual supplements of 400 IU of vitamin E every other day and 500 mg of vitamin C daily.

MAIN OUTCOME MEASURES

Prostate and total cancer.

RESULTS

During a mean follow-up of 8.0 years, there were 1008 confirmed incident cases of prostate cancer and 1943 total cancers. Compared with placebo, vitamin E had no effect on the incidence of prostate cancer (active and placebo vitamin E groups, 9.1 and 9.5 events per 1000 person-years; hazard ratio [HR], 0.97; 95% confidence interval [CI], 0.85-1.09; P = .58) or total cancer (active and placebo vitamin E groups, 17.8 and 17.3 cases per 1000 person-years; HR, 1.04; 95% CI, 0.95-1.13; P = .41). There was also no significant effect of vitamin C on total cancer (active and placebo vitamin C groups, 17.6 and 17.5 events per 1000 person-years; HR, 1.01; 95% CI, 0.92-1.10; P = .86) or prostate cancer (active and placebo vitamin C groups, 9.4 and 9.2 cases per 1000 person-years; HR, 1.02; 95% CI, 0.90-1.15; P = .80). Neither vitamin E nor vitamin C had a significant effect on colorectal, lung, or other site-specific cancers. Adjustment for adherence and exclusion of the first 4 or 6 years of follow-up did not alter the results. Stratification by various cancer risk factors demonstrated no significant modification of the effect of vitamin E on prostate cancer risk or either agent on total cancer risk.

CONCLUSIONS

In this large, long-term trial of male physicians, neither vitamin E nor C supplementation reduced the risk of prostate or total cancer. These data provide no support for the use of these supplements for the prevention of cancer in middle-aged and older men.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00270647.

Vitamins C and E and beta carotene supplementation and cancer risk: a randomized controlled trial

BACKGROUND

Observational studies suggested that a diet high in fruits and vegetables, both of which are rich with antioxidants, may prevent cancer development. However, findings from randomized trials of the association between antioxidant use and cancer risk have been mostly negative.

METHODS

From 8171 women who were randomly assigned in the Women's Antioxidant Cardiovascular Study, a double-blind, placebo-controlled 2 x 2 x 2 factorial trial of vitamin C (500 mg of ascorbic acid daily), natural-source vitamin E (600 IU of alpha-tocopherol every other day), and beta carotene (50 mg every other day), 7627 women who were free of cancer before random assignment were selected for this study. Diagnoses and deaths from cancer at a specific site were confirmed by use of hospital reports and the National Death Index. Cox proportional hazards regression models were used to assess hazard ratios (represented as relative risks [RRs]) of common cancers associated with use of antioxidants, either individually or in combination. Subgroup analyses were conducted to determine if duration of use modified the association of supplement use with cancer risk. All statistical tests were two-sided.

RESULTS

During an average 9.4 years of treatment, 624 women developed incident invasive cancer and 176 women died from cancer. There were no statistically significant effects of use of any antioxidant on total cancer incidence. Compared with the placebo group, the RRs were 1.11 (95% confidence interval [CI] = 0.95 to 1.30) in the vitamin C group, 0.93 (95% CI = 0.79 to 1.09) in the vitamin E group, and 1.00 (95% CI = 0.85 to 1.17) in the beta carotene group. Similarly, no effects of these antioxidants were observed on cancer mortality. Compared with the placebo group, the RRs were 1.28 (95% CI = 0.95 to 1.73) in the vitamin C group, 0.87 (95% CI = 0.65 to 1.17) in the vitamin E group, and 0.84 (95% CI = 0.62 to 1.13) in the beta carotene group. Duration and combined use of the three antioxidants also had no effect on cancer incidence and cancer death.

CONCLUSIONS

Supplementation with vitamin C, vitamin E, or beta carotene offers no overall benefits in the primary prevention of total cancer incidence or cancer mortality.

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.

Randomized trial of a clinic-based, community-supported, lifestyle intervention to improve physical activity and diet: the North Carolina enhanced WISEWOMAN project

OBJECTIVE

To determine if a clinic-based behavioral intervention program for low-income mid-life women that emphasizes use of community resources will increase moderate intensity physical activity (PA) and improve dietary intake.

METHODS

Randomized trial conducted from May 2003 to December 2004 at one community health center in Wilmington, NC. A total of 236 women, ages 40-64, were randomized to receive an Enhanced Intervention (EI) or Minimal Intervention (MI). The EI consisted of an intensive phase (6 months) including 2 individual counseling sessions, 3 group sessions, and 3 phone calls from a peer counselor followed by a maintenance phase (6 months) including 1 individual counseling session and 7 monthly peer counselor calls. Both phases included efforts to increase participants' use of community resources that promote positive lifestyle change. The MI consisted of a one-time mailing of pamphlets on diet and PA. Outcomes, measured at 6 and 12 months, included the comparison of moderate intensity PA between study groups as assessed by accelerometer (primary outcome) and questionnaire, and dietary intake assessed by questionnaire and serum carotenoids (6 months only).

RESULTS

For accelerometer outcomes, follow-up was 75% at 6 months and 73% at 12 months. Though moderate intensity PA increased in the EI and decreased in the MI, the difference between groups was not statistically significant (p=0.45; multivariate model, p=0.08); however, moderate intensity PA assessed by questionnaire (92% follow-up at 6 months and 75% at 12 months) was greater in the EI (p=0.01; multivariate model, p=0.001). For dietary outcomes, follow-up was 90% for questionnaire and 92% for serum carotenoids at 6 months and 74% for questionnaire at 12 months. Dietary intake improved more in the EI compared to the MI (questionnaire at 6 and 12 months, p<0.001; serum carotenoid index, p=0.05; multivariate model, p=0.03).

CONCLUSION

The EI did not improve objectively measured PA, but was associated with improved self-reported and objective measures of dietary intake.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Animal and physiological research as well as observational studies suggest that antioxidant supplements may improve survival.

OBJECTIVES

To assess the effect of antioxidant supplements on mortality in primary or secondary prevention randomised clinical trials.

SEARCH STRATEGY

We searched The Cochrane Library (Issue 3, 2005), MEDLINE (1966 to October 2005), EMBASE (1985 to October 2005), and the Science Citation Index Expanded (1945 to October 2005). We scanned bibliographies of relevant publications and wrote to pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention. Included participants were either healthy (primary prevention trials) or had any disease (secondary prevention trials).

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Trials with adequate randomisation, blinding, and follow-up were classified as having a low risk of bias. Random-effects and fixed-effect meta-analyses were performed. Random-effects meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Sixty-seven randomised trials with 232,550 participants were included. Forty-seven trials including 180,938 participants had low risk of bias. Twenty-one trials included 164,439 healthy participants. Forty-six trials included 68111 participants with various diseases (gastrointestinal, cardiovascular, neurological, ocular, dermatological, rheumatoid, renal, endocrinological, or unspecified). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects meta-analysis (relative risk [RR] 1.02, 95% confidence interval [CI] 0.99 to 1.06), but significantly increased mortality in a fixed-effect model (RR 1.04, 95% CI 1.02 to 1.06). In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. In the trials with a low risk of bias, the antioxidant supplements significantly increased mortality (RR 1.05, 95% CI 1.02 to 1.08). When the different antioxidants were assessed separately, analyses including trials with a low risk of bias and excluding selenium trials found significantly increased mortality by vitamin A (RR 1.16, 95% CI 1.10 to 1.24), beta-carotene (RR 1.07, 95% CI 1.02 to 1.11), and vitamin E (RR 1.04, 95% CI 1.01 to 1.07), but no significant detrimental effect of vitamin C (RR 1.06, 95% CI 0.94 to 1.20). Low-bias risk trials on selenium found no significant effect on mortality (RR 0.91, 95% CI 0.76 to 1.09).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Vitamin A, beta-carotene, and vitamin E may increase mortality. Future randomised trials could evaluate the potential effects of vitamin C and selenium for primary and secondary prevention. Such trials should be closely monitored for potential harmful effects. Antioxidant supplements need to be considered medicinal products and should undergo sufficient evaluation before marketing.