A randomized controlled trial for chemoprevention of gastric cancer in high-risk Japanese population; study design, feasibility and protocol modification

Antioxidant vitamin and mineral supplements for preventing age-related macular degeneration

BACKGROUND

There is inconclusive evidence from observational studies to suggest that people who eat a diet rich in antioxidant vitamins (carotenoids, vitamins C, and E) or minerals (selenium and zinc) may be less likely to develop age-related macular degeneration (AMD).

OBJECTIVES

To determine whether or not taking antioxidant vitamin or mineral supplements, or both, prevent the development of AMD.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2017, Issue 2), MEDLINE Ovid (1946 to 29 March 2017), Embase Ovid (1947 to 29 March 2017), AMED (Allied and Complementary Medicine Database) (1985 to 29 March 2017), OpenGrey (System for Information on Grey Literature in Europe) (www.opengrey.eu/); searched 29 March 2017, the ISRCTN registry (www.isrctn.com/editAdvancedSearch); searched 29 March 2017, ClinicalTrials.gov (www.clinicaltrials.gov); searched 29 March 2017 and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en); searched 29 March 2017. We did not use any date or language restrictions in the electronic searches for trials.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) comparing an antioxidant vitamin or mineral supplement (alone or in combination) to control.

DATA COLLECTION AND ANALYSIS

Both review authors independently assessed risk of bias in the included studies and extracted data. One author entered data into RevMan 5; the other author checked the data entry. We pooled data using a fixed-effect model. We graded the certainty of the evidence using GRADE.

MAIN RESULTS

We included a total of five RCTs in this review with data available for 76,756 people. The trials were conducted in Australia, Finland, and the USA, and investigated vitamin C, vitamin E, beta-carotene, and multivitamin supplements. All trials were judged to be at low risk of bias.Four studies reported the comparison of vitamin E with placebo. Average treatment and follow-up duration ranged from 4 to 10 years. Data were available for a total of 55,614 participants. There was evidence that vitamin E supplements do not prevent the development of any AMD (risk ratio (RR) 0.97, 95% confidence interval (CI) 0.90 to 1.06; high-certainty evidence), and may slightly increase the risk of late AMD (RR 1.22, 95% CI 0.89 to 1.67; moderate-certainty evidence) compared with placebo. Only one study (941 participants) reported data separately for neovascular AMD and geographic atrophy. There were 10 cases of neovascular AMD (RR 3.62, 95% CI 0.77 to 16.95; very low-certainty evidence), and four cases of geographic atrophy (RR 2.71, 95% CI 0.28 to 26.0; very low-certainty evidence). Two trials reported similar numbers of adverse events in the vitamin E and placebo groups. Another trial reported excess of haemorrhagic strokes in the vitamin E group (39 versus 23 events, hazard ratio 1.74, 95% CI 1.04 to 2.91, low-certainty evidence).Two studies reported the comparison of beta-carotene with placebo. These studies took place in Finland and the USA. Both trials enrolled men only. Average treatment and follow-up duration was 6 years and 12 years. Data were available for a total of 22,083 participants. There was evidence that beta-carotene supplements did not prevent any AMD (RR 1.00, 95% CI 0.88 to 1.14; high-certainty evidence) nor have an important effect on late AMD (RR 0.90, 95% CI 0.65 to 1.24; moderate-certainty evidence). Only one study (941 participants) reported data separately for neovascular AMD and geographic atrophy. There were 10 cases of neovascular AMD (RR 0.61, 95% CI 0.17 to 2.15; very low-certainty evidence) and 4 cases of geographic atrophy (RR 0.31 95% CI 0.03 to 2.93; very low-certainty evidence). Beta-carotene was associated with increased risk of lung cancer in people who smoked.One study reported the comparison of vitamin C with placebo, and multivitamin (Centrum Silver) versus placebo. This was a study in men in the USA with average treatment duration and follow-up of 8 years for vitamin C and 11 years for multivitamin. Data were available for a total of 14,236 participants. AMD was assessed by self-report followed by medical record review. There was evidence that vitamin C supplementation did not prevent any AMD (RR 0.96, 95% CI 0.79 to 1.18; high-certainty evidence) or late AMD (RR 0.94, 0.61 to 1.46; moderate-certainty evidence). There was a slight increased risk of any AMD (RR 1.21, 95% CI 1.02 to 1.43; moderate-certainty evidence) and late AMD (RR 1.22, 95% CI 0.88 to 1.69; moderate-certainty evidence) in the multivitamin group. Neovascular AMD and geographic atrophy were not reported separately. Adverse effects were not reported but there was possible increased risk of skin rashes in the multivitamin group.Adverse effects were not consistently reported in these eye studies, but there is evidence from other large studies that beta-carotene increases the risk of lung cancer in people who smoke or who have been exposed to asbestos.None of the studies reported quality of life or resource use and costs.

AUTHORS' CONCLUSIONS

Taking vitamin E or beta-carotene supplements will not prevent or delay the onset of AMD. The same probably applies to vitamin C and the multivitamin (Centrum Silver) investigated in the one trial reported to date. There is no evidence with respect to other antioxidant supplements, such as lutein and zeaxanthin. Although generally regarded as safe, vitamin supplements may have harmful effects, and clear evidence of benefit is needed before they can be recommended. People with AMD should see the related Cochrane Review on antioxidant vitamin and mineral supplements for slowing the progression of AMD, written by the same review team.

Vitamin C for preventing and treating the common cold

BACKGROUND

Vitamin C (ascorbic acid) for preventing and treating the common cold has been a subject of controversy for 70 years.

OBJECTIVES

To find out whether vitamin C reduces the incidence, the duration or severity of the common cold when used either as a continuous regular supplementation every day or as a therapy at the onset of cold symptoms.

SEARCH METHODS

We searched CENTRAL 2012, Issue 11, MEDLINE (1966 to November week 3, 2012), EMBASE (1990 to November 2012), CINAHL (January 2010 to November 2012), LILACS (January 2010 to November 2012) and Web of Science (January 2010 to November 2012). We also searched the U.S. National Institutes of Health trials register and WHO ICTRP on 29 November 2012.

SELECTION CRITERIA

We excluded trials which used less than 0.2 g per day of vitamin C and trials without a placebo comparison. We restricted our review to placebo-controlled trials.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data. We assessed 'incidence' of colds during regular supplementation as the proportion of participants experiencing one or more colds during the study period. 'Duration' was the mean number of days of illness of cold episodes.

MAIN RESULTS

Twenty-nine trial comparisons involving 11,306 participants contributed to the meta-analysis on the risk ratio (RR) of developing a cold whilst taking vitamin C regularly over the study period. In the general community trials involving 10,708 participants, the pooled RR was 0.97 (95% confidence interval (CI) 0.94 to 1.00). Five trials involving a total of 598 marathon runners, skiers and soldiers on subarctic exercises yielded a pooled RR of 0.48 (95% CI 0.35 to 0.64).Thirty-one comparisons examined the effect of regular vitamin C on common cold duration (9745 episodes). In adults the duration of colds was reduced by 8% (3% to 12%) and in children by 14% (7% to 21%). In children, 1 to 2 g/day vitamin C shortened colds by 18%. The severity of colds was also reduced by regular vitamin C administration.Seven comparisons examined the effect of therapeutic vitamin C (3249 episodes). No consistent effect of vitamin C was seen on the duration or severity of colds in the therapeutic trials.The majority of included trials were randomised, double-blind trials. The exclusion of trials that were either not randomised or not double-blind had no effect on the conclusions.

AUTHORS' CONCLUSIONS

The failure of vitamin C supplementation to reduce the incidence of colds in the general population indicates that routine vitamin C supplementation is not justified, yet vitamin C may be useful for people exposed to brief periods of severe physical exercise. Regular supplementation trials have shown that vitamin C reduces the duration of colds, but this was not replicated in the few therapeutic trials that have been carried out. Nevertheless, given the consistent effect of vitamin C on the duration and severity of colds in the regular supplementation studies, and the low cost and safety, it may be worthwhile for common cold patients to test on an individual basis whether therapeutic vitamin C is beneficial for them. Further therapeutic RCTs are warranted.

Vitamin C supplementation in relation to inflammation in individuals with atrophic gastritis: a randomised controlled trial in Japan

Evidence has shown that both C-reactive protein (CRP) and serum amyloid component A (SAA) are increased in individuals with gastritis and stomach cancer. Controlling the level of these biomarkers by inhibiting the gastric infection with high doses of ascorbic acid may reduce the risk of carcinogenesis. A population-based double-blind randomised controlled trial in a Japanese population with atrophic gastritis in an area of high stomach cancer incidence was conducted between 1995 and 2000. Daily doses of 50 or 500 mg vitamin C were given, and 120 and 124 participants completed the 5-year study, respectively. Although serum ascorbic acid was higher in the high-dosage group (1.73 (SD 0.46) μg/l) than in the low-dosage group (1.49 (SD 0.29) μg/l, P< 0.001), at the end of the study, no significant difference was observed for CRP between the low- and high-dosage groups (0.39 (95 % CI 0.04, 4.19) mg/l and 0.38 (95 % CI 0.03, 4.31) mg/l, respectively; P= 0.63) or for SAA between the low- and high-dosage groups (3.94 (95 % CI 1.04, 14.84) μg/ml and 3.85 (95 % CI 0.99, 14.92) μg/ml, respectively; P= 0.61). Vitamin C supplementation may not have a strong effect on reducing infections in individuals with atrophic gastritis.

Antioxidant vitamin and mineral supplements for preventing age-related macular degeneration

BACKGROUND

There is inconclusive evidence from observational studies to suggest that people who eat a diet rich in antioxidant vitamins (carotenoids, vitamins C and E) or minerals (selenium and zinc) may be less likely to develop age-related macular degeneration (AMD).

OBJECTIVES

To examine the evidence as to whether or not taking antioxidant vitamin or mineral supplements prevents the development of AMD.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2011, Issue 12), MEDLINE (January 1950 to January 2012), EMBASE (January 1980 to January 2012), Open Grey (System for Information on Grey Literature in Europe) (www.opengrey.eu/), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). There were no date or language restrictions in the electronic searches for trials. The electronic databases were last searched on 26 January 2012.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) comparing an antioxidant vitamin and/or mineral supplement (alone or in combination) to control.

DATA COLLECTION AND ANALYSIS

Both review authors independently assessed risk of bias in the included studies and extracted data. One author entered data into RevMan 5 and the other author checked the data entry. We pooled data using a fixed-effect model.

MAIN RESULTS

We included four RCTs in this review; 62,520 people were included in the analyses. The trials were conducted in Australia, Finland and the USA and investigated vitamin E and beta-carotene supplements. Overall the quality of the evidence was high. People who took these supplements were not at decreased (or increased) risk of developing AMD. The pooled risk ratio for any antioxidant supplement in the prevention of any AMD was 0.98 (95% confidence interval 0.89 to 1.08) and for advanced AMD was 1.05 (95% CI 0.80 to 1.39). Similar results were seen when the analyses were restricted to beta-carotene and alpha-tocopherol alone.

AUTHORS' CONCLUSIONS

There is accumulating evidence that taking vitamin E or beta-carotene supplements will not prevent or delay the onset of AMD. There is no evidence with respect to other antioxidant supplements, such as vitamin C, lutein and zeaxanthin, or any of the commonly marketed multivitamin combinations. Although generally regarded as safe, vitamin supplements may have harmful effects and clear evidence of benefit is needed before they can be recommended. People with AMD should see the related Cochrane review 'Antioxidant vitamin and mineral supplements for slowing the progression of age-related macular degeneration' written by the same review team.

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.

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.

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.

Antioxidant vitamin and mineral supplements for preventing age-related macular degeneration

BACKGROUND

Some observational studies have suggested that people who eat a diet rich in antioxidant vitamins (carotenoids, vitamins C and E) or minerals (selenium and zinc) may be less likely to develop age-related macular degeneration (AMD).

OBJECTIVES

The aim of this review was to examine the evidence as to whether or not taking vitamin or mineral supplements prevents the development of AMD.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Group Trials Register) in The Cochrane Library (2007, Issue 3), MEDLINE (1966 to August 2007), SIGLE (1980 to 2005/03), EMBASE (1980 to August 2007), National Research Register (2007, Issue 3), AMED (1985 to January 2006) and PubMed (on 24 January 2006 covering last 60 days), reference lists of identified reports and the Science Citation Index. We contacted investigators and experts in the field for details of unpublished studies.

SELECTION CRITERIA

We included all randomised trials comparing an antioxidant vitamin and/or mineral supplement (alone or in combination) to control. We included only studies where supplementation had been given for at least one year.

DATA COLLECTION AND ANALYSIS

Both review authors independently extracted data and assessed trial quality. Data were pooled using a fixed-effect model.

MAIN RESULTS

Three randomised controlled trials were included in this review (23,099 people randomised). These trials investigated alpha-tocopherol and beta-carotene supplements. There was no evidence that antioxidant vitamin supplementation prevented or delayed the onset of AMD. The pooled risk ratio for any age-related maculopathy (ARM) was 1.04 (95% CI 0.92 to 1.18), for AMD (late ARM) was 1.03 (95% CI 0.74 to 1.43). Similar results were seen when the analyses were restricted to beta-carotene and alpha-tocopherol.

AUTHORS' CONCLUSIONS

There is no evidence to date that the general population should take antioxidant vitamin and mineral supplements to prevent or delay the onset of AMD. There are several large ongoing trials. People with AMD should see the related Cochrane review "Antioxidant vitamin and mineral supplements for slowing the progression of age-related macular degeneration" written by the same author.

Vitamin C for preventing and treating the common cold

BACKGROUND

The role of vitamin C (ascorbic acid) in the prevention and treatment of the common cold has been a subject of controversy for 60 years, but is widely sold and used as both a preventive and therapeutic agent.

OBJECTIVES

To discover whether oral doses of 0.2 g or more daily of vitamin C reduces the incidence, duration or severity of the common cold when used either as continuous prophylaxis or after the onset of symptoms.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 4, 2006); MEDLINE (1966 to December 2006); and EMBASE (1990 to December 2006).

SELECTION CRITERIA

Papers were excluded if a dose less than 0.2 g per day of vitamin C was used, or if there was no placebo comparison.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed trial quality. 'Incidence' of colds during prophylaxis was assessed as the proportion of participants experiencing one or more colds during the study period. 'Duration' was the mean days of illness of cold episodes.

MAIN RESULTS

Thirty trial comparisons involving 11,350 study participants contributed to the meta-analysis on the relative risk (RR) of developing a cold whilst taking prophylactic vitamin C. The pooled RR was 0.96 (95% confidence intervals (CI) 0.92 to 1.00). A subgroup of six trials involving a total of 642 marathon runners, skiers, and soldiers on sub-arctic exercises reported a pooled RR of 0.50 (95% CI 0.38 to 0.66). Thirty comparisons involving 9676 respiratory episodes contributed to a meta-analysis on common cold duration during prophylaxis. A consistent benefit was observed, representing a reduction in cold duration of 8% (95% CI 3% to 13%) for adults and 13.6% (95% CI 5% to 22%) for children. Seven trial comparisons involving 3294 respiratory episodes contributed to the meta-analysis of cold duration during therapy with vitamin C initiated after the onset of symptoms. No significant differences from placebo were seen. Four trial comparisons involving 2753 respiratory episodes contributed to the meta-analysis of cold severity during therapy and no significant differences from placebo were seen.

AUTHORS' CONCLUSIONS

The failure of vitamin C supplementation to reduce the incidence of colds in the normal population indicates that routine mega-dose prophylaxis is not rationally justified for community use. But evidence suggests that it could be justified in people exposed to brief periods of severe physical exercise or cold environments.

Long-term vitamin C supplementation has no markedly favourable effect on serum lipids in middle-aged Japanese subjects

Antioxidant vitamins have been reported to be associated with an improvement in blood lipid profiles, but results are not consistent. The present study was designed to determine whether long-term vitamin C supplementation could alter serum lipid concentrations in subjects who completed a 5-year population-based double-blind intervention trial. A total of 439 Japanese subjects with atrophic gastritis initially participated in the trial using vitamin C and β-carotene to prevent gastric cancer. Before and upon early termination of β-carotene supplementation, 134 subjects dropped out of the trial; finally, 161 subjects assigned to the high-dose group (500 mg vitamin C/d) and 144 subjects assigned to the low-dose group (50 mg vitamin C/d) were studied. No favourable effect of vitamin C supplementation on serum concentrations of total cholesterol, HDL- and LDL-cholesterol, and triacylglycerol was observed, although high-dose vitamin C supplementation increased serum vitamin C concentrations substantially. Among women, the mean change in serum triacylglycerol decreased (−0·12 mmol/l, 95 % CI −0·32, 0·09) in the high-dose group, but increased (+0·12 mmol/l, 95 % CI 0·03, 0·22) in the low-dose group. In addition, the mean change in serum triacylglycerol among women with hypertriacylglycerolaemia was statistically significant (−1·21, 95 % CI −2·38, −0·05) after high-dose vitamin C supplementation. The 5-year vitamin C supplementation had no markedly favourable effects on the serum lipid and lipoprotein profile. However, our present results do not preclude the possibility that vitamin C supplementation may decrease triacylglycerol concentrations among women with hypertriacylglycerolaemia.

Effect of vitamin C on common cold: randomized controlled trial

OBJECTIVE

To investigate the relationship between the common cold and vitamin C supplementation.

DESIGN

A double-blind, 5-year randomized controlled trial.

SETTING

A village in Akita prefecture, one of the regions in Japan with the highest mortality from gastric cancer.

SUBJECTS

Participants in annual screening programs for circulatory diseases conducted under the National Health and Welfare Services Law for the Aged, and diagnosed as having atrophic gastritis. Of the 439 eligible subjects, 144 and 161 were assigned to receive 50 or 500 mg of vitamin C, respectively, after protocol amendment. During the supplementation phase, 61 dropped out, and 244 completed the trial.

INTERVENTION

Daily vitamin C supplementation of 50 mg (low-dose group) or 500 mg (high-dose group).

RESULTS

Total number of common colds (per 1000 person-months) was 21.3 and 17.1 for the low- and high-dose groups, respectively. After adjustment for several factors, the relative risks (95% confidence interval (CI)) of suffering from a common cold three or more times during the survey period was 0.34 (0.12-0.97) for the high-dose group. No apparent reduction was seen for the severity and duration of the common cold.

CONCLUSION

A randomized, controlled 5-year trial suggests that vitamin C supplementation significantly reduces the frequency of the common cold but had no apparent effect on the duration or severity of the common cold. However, considering several limitations due to protocol amendment, the findings should be interpreted with caution.

Designing a Randomized Phase I/II Prostate Cancer Chemoprevention Trial Using 1??-Hydroxy-24-Ethyl-Cholecalciferol, an Analogue of Vitamin D3

Prostate cancer continues to be a significant source of morbidity and mortality among older men. One possible means of reducing its impact on overall health and vitality is via cancer chemoprevention, both in the population that is unaffected but at some risk and in those who have undergone some form of curative therapy after the onset of the disease. Chemoprevention holds significant promise, but large phase III clinical trials evaluating chemopreventive agents in prostate cancer can require vast numbers of enrollees and require the commitment of significant financial resources and time before any therapeutic benefit may become apparent. One technique to shorten the time required for chemoprevention clinical trials is to use surrogate endpoint biomarkers in place of the currently used actual endpoints of cancer incidence or survival. The validation of such surrogate endpoint biomarkers will require small, well-designed phase I and/or II trials to accumulate data on the modulation of the surrogate biomarkers and the endpoints of cancer incidence or survival by the chemopreventive agent. Careful statistical correlation and clinical validation of the data will then allow us to justify the use such surrogates in place of the actual endpoint in large, randomized trials, potentially shortening trial duration, improving financial efficiency, and accelerating approval of the chemopreventive agent. To that end, we first review the theoretical construct of cancer chemoprevention trials with particular reference to prostate cancer. We thereafter describe the design of a small, randomized, double-blinded, placebo-controlled phase I/II clinical trial of an analogue of vitamin D, vitamin D5, which we believe could serve as a model for data accumulation on surrogate biomarkers and correlation with other clinical endpoints.

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.

Effect of five-year supplementation of vitamin C on serum vitamin C concentration and consumption of vegetables and fruits in middle-aged Japanese: a randomized controlled trial

OBJECTIVE

This study was aimed at evaluating the effect of long-term vitamin C supplementation on serum and dietary vitamin C and identifying the factors associated with change in serum concentration.

METHODS

A total of 439 subjects with atrophic gastritis initially participated in a randomized clinical trial using vitamin C and beta-carotene to prevent gastric cancer. We originally randomized the participants into four treatment groups using a 2x2 factorial design, whereby 0 or 15 mg/day beta-carotene and 50 or 500 mg/day vitamin C were administered in a double-blind manner. The beta-carotene component was terminated early after a mean treatment duration of four months. Before and upon early termination of beta-carotene supplementation, 134 subjects dropped out this trial, while 120 and 124 subjects took the vitamin C supplement at either 50 mg or 500 mg daily for five years.

RESULTS

Changes in serum vitamin C were significantly higher in the high-dose group (38.5% increase, 95% CI = 27.0-49.9) than in the low-dose group (13.0% increase, 5.1-20.9) or in the dropout group (3.3% increase, -2.1-8.6) after five-year supplementation. The serum vitamin C at baseline was negatively associated with changes in serum vitamin C (p < 0.0001), while high-dose (p < 0.0001) and low-dose (p < 0.05) supplementation and female gender (p < 0.001) were positively associated. Dietary intake of vitamin C in the supplementation group was almost identical before and after five-year supplementation of vitamin C (2.31 mg/day decrease, 95% CI = -15.3-10.7), while a 17.7 mg/day decrease (95% CI = -44.2-8.86) was observed in the drop-out group.

CONCLUSION

Five-year vitamin C supplementation induces a remarkable increase in serum vitamin C concentration, and our intervention program appears to have no effect on dietary vitamin C intake.

The effect of 5-year vitamin C supplementation on serum pepsinogen level and Helicobacter pylori infection

We conducted a population-based, double-blind, randomized controlled trial to examine the effect of vitamin C supplementation on serum pepsinogen (PG) level, Helicobacter pylori (H. pylori ) infection, and cytotoxin-associated gene A (Cag A) status. Subjects aged 40 to 69 years living in one village in Akita prefecture, a high-risk area for gastric cancer in Japan, were recruited through annual health check-up programs. Among 635 subjects diagnosed as having chronic gastritis on the basis of serum PG levels, after excluding ineligible cases, 439 subjects were assigned to one of four groups using a 2 x 2 factorial design (0 or 15 mg/day beta-carotene and 50 or 500 mg/day vitamin C). However, based on the results from two beta-carotene trials in the United States, we discontinued beta-carotene (vitamin C supplementation was continued). Finally, 120 subjects in the low-dose group (vitamin C 50 mg), and 124 subjects in the high-dose group (vitamin C 500 mg) completed the 5-year supplementation. The difference in the change of PGI/II ratio between baseline and after 5-year follow up was statistically significant between the intervention groups among those who completed the supplementation: - 0.25 for the low-dose group and - 0.13 for the high-dose group (P = 0.046). To conclude, vitamin C supplementation may protect against progression of gastric mucosal atrophy.

Lack of long-term effect of vitamin C supplementation on blood pressure

In a double-blinded randomized controlled trial, we investigated the long-term effect of vitamin C supplementation on blood pressure. A total of 439 Japanese subjects with atrophic gastritis initially participated in the trial using vitamin C and beta-carotene to prevent gastric cancer. Before and on early termination of beta-carotene supplementation, 134 subjects dropped out of this trial, whereas 120 and 124 subjects took the vitamin C supplement daily at either 50 mg or 500 mg, respectively, for 5 years. Before supplementation, neither systolic nor diastolic blood pressure was significantly related with the serum vitamin C concentration. This relationship was unchanged after adjustment for age, body mass index, and alcohol intake or after stratification by gender. After 5 years, systolic blood pressure significantly increased in groups, regardless of vitamin C dose, compared with baseline. Systolic blood pressure in the high-dose group (500 mg daily) increased from 125.4 to 131.7 mm Hg (5.88 mm Hg increase; 95% confidence interval [CI], 3.11 to 8.65). This value was similar with that of the low-dose group (5.73 mm Hg increase; 95% CI, 2.62 to 8.83) and of the dropout group (4.52 mm Hg increase; 95% CI, 1.26 to 7.77). There was no difference in change of diastolic blood pressure among the 3 groups. In conclusion, we observed no reduction in blood pressure with long-term moderate doses (500 mg/day) of vitamin C supplementation in a high-risk population for stomach cancer and stroke.

Prostaglandin inhibitors and the chemoprevention of noncolonic malignancy

Much has been learned about the role of NSAIDs as cancer preventives through epidemiologic and experimental studies. The pathways of carcinogenesis in the gastrointestinal tract are initiated by many different genetic, environmental, infective, and lifestyle factors. It is possible that the final common pathway of all these malignancies may have some common features. It is conceivable that head and neck, esophageal, gastric, and colorectal epithelial carcinogenesis all are influenced by or require COX-2 up-regulation as a step toward transformation. Intuitively, it is possible that selective COX-2 inhibitors may have a preventive role in all these epithelial malignancies. Today's challenge is to translate this information into clinical trials to define what role, if any, COX inhibition might play in the prevention of these malignancies.

Effects of three-month oral supplementation of beta-carotene and vitamin C on serum concentrations of carotenoids and vitamins in middle-aged subjects: a pilot study for a randomized controlled trial to prevent gastric cancer in high-risk Japanese population

Prior to a randomized controlled trial to prevent gastric cancer by oral supplementation of beta-carotene and vitamin C in a high-risk Japanese population, we examined the serum response to three-month oral supplementation of beta-carotene (0, 3, 30 mg / day) and vitamin C (0, 50, 1000 mg / day) by a three-by-three factorial design using 54 subjects (age range = 40 - 69 years). Serum concentrations of carotenoids, alpha-tocopherol, and ascorbic acid were examined at baseline, and one, two, and three-month points. Both serum beta-carotene and ascorbic acid were significantly higher in high-dose groups than in each placebo group during the supplementation. The serum beta-carotene increased gradually (597 - 830% increase) during the study, whereas the serum ascorbic acid reached nearly a steady-state at the one-month point and remained stable thereafter (88 - 95% increase). No statistically significant interaction between beta-carotene and vitamin C supplementations was observed either for serum beta-carotene or for serum ascorbic acid. Among carotenoids and alpha-tocopherol examined, serum lycopene in the high-dose beta-carotene group was significantly higher than in the placebo group at all points. No unfavorable change in carotenoids and alpha-tocopherol was observed in any group.

Antioxidant vitamin and mineral supplementation for preventing age-related macular degeneration

BACKGROUND

Some observational studies have suggested that people who eat a diet rich in antioxidant vitamins (carotenoids, vitamins C and E) or minerals (selenium and zinc) may be less likely to develop age-related macular degeneration.

OBJECTIVES

The aim of this review is to examine the evidence as to whether or not taking vitamin or mineral supplements prevents the development of age-related macular degeneration.

SEARCH STRATEGY

We searched the Cochrane Eyes and Vision Group specialised register, the Cochrane Controlled Trials Register - Central, MEDLINE, reference lists of identified reports and the Science Citation Index. We contacted investigators and experts in the field for details of unpublished studies. The most recent searches were conducted in June 1999.

SELECTION CRITERIA

All randomised trials comparing an antioxidant vitamin and/or mineral supplement (alone or in combination) to control were included. We included only studies where supplementation had been given for at least one year.

DATA COLLECTION AND ANALYSIS

Both reviewers independently extracted data and assessed trial quality. Currently there is only one published trial included in the review so no data synthesis was conducted.

MAIN RESULTS

One trial is included in the review. This was a primary prevention trial in Finnish male smokers with four treatment groups: alpha-tocopherol alone, beta-carotene alone, alpha-tocopherol and beta-carotene, placebo. The add-on maculopathy study was conducted in a subset of the main trial cohort. 269 cases of maculopathy (14 late stage age-related macular degeneration) were identified. There was no association of age-related macular degeneration with treatment.

REVIEWER'S CONCLUSIONS

There is no evidence to date that people without age-related macular degeneration should take antioxidant vitamin and mineral supplements to prevent or delay the onset of the disease. The results of five large ongoing trials are awaited.

Tea polyphenol intake and changes in serum pepsinogen levels

Following a phase I study, a phase II study was conducted to evaluate the effects of two different doses of tea polyphenols on serum pepsinogen levels. Subjects were patients aged 40 to 69 years who had undergone gastroscopy between 1995 and 1997 at Aichi Cancer Center Hospital, and had been found to have no disease requiring medication. Those with pepsinogen I < 70 ng/ml and pepsinogen I/II ratio < 6 were included in this study. Capsules containing 100 mg of tea polyphenols were administered for 1 year: 1 capsule per day for 101 patients (42 males and 59 females), and 6 capsules (equivalent to 10 cups) per day for 83 patients (30 males and 53 females). The enrollment of the 1 capsule group preceded that of the 6 capsule group, in which re-participation was allowed. Blood samples were obtained 1 year after participation from 86 participants of the 1 capsule group and 77 participants (43 new participants and 34 re-participants) of the 6 capsule group. The compliance in polyphenol capsule intake ranged from 11.4 to 105.7% (87.6% on average) of the scheduled amount for the 1 capsule group and 3.2 to 112.3% (77.8% on average) for the 6 capsule group. No serious polyphenol-related adverse effects were reported. The difference in pepsinogen I between before and after 1 year intake of the polyphenol was 3.1 ng/ml for the 43 participants of the 6 capsule group, but 3.5 ng/ml for the 1 capsule group. The mean pepsinogen I/II ratio for the 43 participants increased from 2.37 by 0.08. This increase was not larger than that for the 1 capsule group (from 2.61 by 0.11). Among 34 participants in both interventions, no significant increase in pepsinogen I and I/II ratio for the 6 capsule intervention was observed. This result suggests that additional polyphenol intake for 1 year in Japanese does not improve pepsinogen levels, which are considered to reflect stomach atrophy, a high-risk condition for stomach cancer.