Effects of intermittent or single high-dose vitamin D supplementation on risk of falls and fractures: a systematic review and meta-analysis.

Previous randomized controlled trials have reported inconsistent findings regarding the effects of high-dose vitamin D supplementation on a risk of falls and fractures. This meta-analysis of 15 trials shows that intermittent or single high-dose vitamin D supplementation had no preventive effect on the risk of falls and fractures and might even increase the risk of falls. PURPOSE: Randomized controlled trials (RCTs) have reported controversial findings regarding the associations between intermittent or single high-dose vitamin D supplementation and a risk of falls and fractures in adults. This study aimed to investigate those associations using a systematic review and meta-analysis. METHODS: We searched PubMed, EMBASE, and Cochrane Library from inception to May 25, 2022. Data were extracted for a random-effects meta-analysis to calculate a pooled relative risk (RR) with a 95% confidence interval (CI). RESULTS: Out of 527 articles, a total of 15 RCTs were included in the final analysis. In a meta-analysis of RCTs, intermittent or single high-dose vitamin D supplementation showed no significant beneficial effect in the prevention of either falls (RR, 1.03 [95% CI, 0.98-1.09]; I2 = 56.6%; n = 11) or fractures (RR, 0.99 [95% CI, 0.87-1.14]; I2 = 48.3%; n = 11). Among the subgroup meta-analyses by various factors, intermittent or single high-dose vitamin D supplementation reduced the risk of fractures in the subgroup meta-analysis of RCTs that included fewer than 1000 participants (RR, 0.74 [95% CI 0.57-0.96]; I2 = 0.0%; n = 5). However, its beneficial effect was not observed in those including 1000 or more participants (RR, 1.06 [95% CI 0.92-1.21]; I2 = 57.5%; n = 6). In contrast, intermittent or single high-dose vitamin D3 supplementation increased the risk of falls on the borderline of statistical significance (RR, 1.06 [95% CI 0.99-1.15]; P = 0.051; I2 = 50.0%; n = 7). CONCLUSIONS: Intermittent or single high-dose vitamin D supplementation had no preventive effect on the risk of falls and fractures and might even increase the risk of falls.

Effect of Coffee Consumption on Risk of Coronary Heart Disease in a Systematic Review and Meta-Analysis of Prospective Cohort Studies.

Previous prospective studies have reported inconsistent findings on the association between coffee consumption and the risk of coronary heart disease (CHD). This study aimed to investigate their association using a meta-analysis of prospective studies. We searched PubMed and EMBASE for prospective cohort studies of the association between coffee consumption and the risk of CHD in the general population. We conducted a random-effects meta-analysis and also subgroup meta-analyses by various factors. Of 870 studies searched from databases, 32 prospective cohort studies were included in the final analysis. In the main meta-analysis of all studies, no significant association between coffee consumption and the risk of CHD was observed (relative risk [RR] 1.05, 95% confidence interval [CI] 0.97 to 1.14, I2 = 64.9%). In the subgroup meta-analyses by gender, coffee consumption significantly increased the risk of CHD in men (RR 1.19, 95% CI 1.05 to 1.35, n = 17), whereas a nonsignificantly decreased risk of CHD was observed in women (RR 0.91, 95% CI 0.77 to 1.08, n = 11). Also, in the subgroup meta-analyses by follow-up period, coffee consumption significantly increased the risk of CHD in the follow-up of 20 years or longer (RR 1.16, 95% CI 1.06 to 1.27, n = 4) regardless of gender. In conclusion, in the current meta-analysis of prospective studies, we found that, overall, no significant association between coffee consumption and the risk of CHD was observed. However, coffee consumption showed a differential effect by gender, with an increased risk of CHD in men and a potentially decreased risk in women.

Coffee Intake and Risk of Hypertension: A Meta-Analysis of Cohort Studies.

BACKGROUND: It remains unclear whether coffee intake is associated with the risk of hypertension. This study aimed to investigate the association between coffee intake and the risk of hypertension by using a meta-analysis of cohort studies. METHODS: PubMed and Embase were searched using keywords in September 2022 to identify studies on coffee intake and the risk of hypertension. RESULTS: We included a total of 13 longitudinal cohort studies, which involved a total of 64,650 incident cases of hypertension among 314,827 participants. In a random effects model meta-analysis of all the studies, coffee intake was not significantly associated with the risk of hypertension (relative risk [RR], 0.97; 95% confidence interval [CI], 0.90­1.05; I² = 58.0%; n = 13). In the subgroup meta-analysis, coffee intake was associated with a decreased risk of hypertension in studies conducted in America (RR, 0.93; 95% CI, 0.87-0.98; I² = 4.6%; n = 5) and in low-quality studies (RR, 0.92; 95% CI, 0.88-0.96; I² = 0.0%; n = 7). In the remaining subgroup meta-analyses by amount of coffee intake, gender, type of coffee (decaffeinated vs. caffeinated), smoking, and years of follow-up, coffee intake was not significantly associated with the risk of hypertension. CONCLUSION: The current meta-analysis showed that coffee intake is not associated with the risk of hypertension.

Efficacy of Vitamin D Supplements in Treatment of Acute Respiratory Infection: A Meta-Analysis for Randomized Controlled Trials.

BACKGROUND: Recent randomized controlled trials (RCTs) have reported inconsistent findings regarding the efficacy of vitamin D supplementation in the treatment of acute respiratory infections (ARIs). This study aimed to investigate the efficacy of vitamin D supplementation in the treatment of ARIs using a meta-analysis of RCTs. METHODS: PubMed, EMBASE, and the Cochrane Library were searched for relevant articles in June 2021. Two of the authors independently assessed the eligibility of the trials. RESULTS: Out of 390 articles retrieved from the databases, we included 18 RCTs, which involved 3648 participants, with 1838 in an intervention group and 1810 in a control group in the final analysis. In the meta-analysis of all the trials, vitamin D supplements had a beneficial effect in the treatment of ARIs (relative risk (RR) = 1.07; 95% confidence interval (CI), 1.01-1.13; I2 = 66.9%). Publication bias was observed in the funnel plot. In the subgroup meta-analysis of high-quality RCTs, no significant efficacy of vitamin D supplements was found (RR = 1.02; 95% CI, 0.98-1.06; I2 = 24.0%). Although statistically significant changes of 7% in the treatment effects were observed, they are not considered as clinically substantial ones. CONCLUSIONS: The current meta-analysis suggests that vitamin D supplements are not clinically effective in the treatment of ARIs.

Efficacy of Vitamin D Supplements in Prevention of Acute Respiratory Infection: A Meta-Analysis for Randomized Controlled Trials.

BACKGROUND: Previous systematic reviews and meta-analyses of randomized controlled trials (RCTs) have reported inconsistent results regarding the efficacy of vitamin D supplements in the prevention of acute respiratory infections (ARIs). METHODS: We investigated these efficacy results by using a meta-analysis of RCTs. We searched PubMed, EMBASE, and the Cochrane Library in June 2021. RESULTS: Out of 390 trials searched from the database, a total of 30 RCTs involving 30,263 participants were included in the final analysis. In the meta-analysis of all the trials, vitamin D supplementation showed no significant effect in the prevention of ARIs (relative risk (RR) 0.96, 95% confidence interval (CI) 0.91-1.01, I2 = 59.0%, n = 30). In the subgroup meta-analysis, vitamin D supplementation was effective in daily supplementation (RR 0.83, 95% CI, 0.73-0.95, I2 = 69.1%, n = 15) and short-term supplementation (RR 0.83, 95% CI, 0.71-0.97, I2 = 66.8%, n = 13). However, such beneficial effects disappeared in the subgroup meta-analysis of high-quality studies (RR 0.89, 95% CI, 0.78-1.02, I2 = 67.0%, n = 10 assessed by the Jadad scale; RR 0.87, 95% CI, 0.66-1.15, I2 = 51.0%, n = 4 assessed by the Cochrane's risk of bias tool). Additionally, publication bias was observed. CONCLUSIONS: The current meta-analysis found that vitamin D supplementation has no clinical effect in the prevention of ARIs.

Effects of Mindfulness-Based Interventions on Mental Health in Nurses: A Meta-Analysis of Randomized Controlled Trials.

Mindfulness as a positive mental health intervention approach has been increasingly applied to nurses. This meta-analysis evaluated the psychological effects of mindfulness-based interventions (MBIs) on mental health in nurses. We searched PubMed, EMBASE, Cochrane, and CINAHL up to February 2020. Randomized controlled trials (RCTs) evaluating the effects of MBIs for nurses were included. Data extraction and the risk of bias assessment were conducted by two authors independently. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were calculated using a random-effects meta-analysis. Of 370 studies retrieve from databases, nine RCTs, which involved 572 participants with 283 in an intervention group and 289 in a control group, were included in the final analysis. Compared to the control groups (no treatment, treatment as usual, or active control), MBIs reduced psychological distress such as anxiety, depression, or stress (SMD = -0.47; 95% CI, -0.67 to -0.32; I2 = 34.7; n = 17) in nurses. Also, MBIs slightly improved psychological wellbeing such as resilience, wellbeing, or quality of life (SMD = 0.28; 95% CI, 0.11 to 0.46; I2 = 0.00; n = 8). However, no statistically significant effects were found in Job related outcomes (SMD = 0.23; 95% CI, -0.01 to 0.47; I2 = 20.5; n = 6). This meta-analysis found that MBIs had beneficial effects on mental health such as psychological distress and wellbeing in nurses.

Gynecological cancer and omega-3 fatty acid intakes: Meta-analysis.

BACKGROUND AND OBJECTIVES: Previous observational epidemiological studies have reported inconsistent findings on the association between dietary intake of omega-3 fatty acids and endocrine-related gynecological cancer including ovarian cancer and endometrial cancer. This study aimed to investigate this association using a metaanalysis of observational studies. METHODS AND STUDY DESIGN: We searched PubMed, EMBASE, and Cochrane library by using keywords related to the topic in December 2019. The pooled odd ratios (pORs), pooled relative risks (pRRs), or pooled hazard ratios (pHRs) with 95% confidence intervals (CIs) were calculated based on a random- effects model. Also, we performed subgroup analyses by methodological quality, type of cancer, study design, and type of omega-3 fatty acids. RESULTS: A total of 10 observational studies with six case-control and four prospective cohort studies were included in the current meta-analysis. In the meta-analysis of all studies, dietary intake of omega-3 fatty acids was not significantly associated with the risk of endometrial and ovarian cancers (pOR/HR, 0.87; 95% CI, 0.73-1.04; I2=67.2%) (highest versus lowest intake). In the subgroup analysis by type of study, no significant association was found in cohort studies (pHR, 1.03; 95% CI, 0.63-1.67, I2=81.9%), whereas dietary intake of omega-3 fatty acids was associated with the decreased risk of endocrine-related gynecological cancers in case-control studies (pOR, 0.81; 95% CI, 0.67 to 0.98, I2=55.7%). CONCLUSIONS: The current metaanalysis of observational studies suggests that dietary intake of omega-3 fatty acids is not significantly associated with the risk of endocrine-related gynecological cancer.

Calcium Supplements and Risk of Cardiovascular Disease: A Meta-Analysis of Clinical Trials.

BACKGROUND: Recent systematic reviews and meta-analyses of randomized, double-blind, placebo-controlled trials (double-blind, placebo-controlled RCTs) have reported controversial findings regarding the associations between calcium supplements on the risk of cardiovascular disease (CVD). This meta-analysis aimed to investigate the association between them. METHODS: We searched PubMed, EMBASE, the Cochrane Library, and the bibliographies of relevant articles for double-blind, placebo-controlled RCTs in November, 2020. Relative risks (RRs) with 95% confidence intervals (CIs) for the risk of cardiovascular disease were calculated using a random effects model. The main outcomes were CVD, coronary heart disease (CHD), and cerebrovascular disease. RESULTS: A total of 13 double-blind, placebo-controlled RCTs (n = 28,935 participants in an intervention group and 14,243 in a control group)) were included in the final analysis. Calcium supplements significantly increased the risk of CVD (RR 1.15, 95% CI 1.06-1.25], I2 = 0.0%, n = 14) and CHD (RR 1.16, 95% CI 1.05-1.28], I2 = 0.0%, n = 9) in double-blind, placebo-controlled RCTs, specifically in healthy postmenopausal women. In the subgroup meta-analysis, dietary calcium intake of 700-1000 mg per day or supplementary calcium intake of 1000 mg per day significantly increased the risk of CVD and CHD. CONCLUSIONS: The current meta-analysis found that calcium supplements increased a risk of CVD by about 15% in healthy postmenopausal women.

Dietary Intake of Omega-3 fatty acids and Endocrine-related Gynecological Cancer: A Meta-Analysis of Observational Studies.

PURPOSE: Previous observational epidemiological studies have reported inconsistent findings on the association between dietary intake of omega-3 fatty acids and endocrine-related gynecological cancer such as ovarian cancer and endometrial cancer. This study aimed to investigate this association using a meta-analysis of observational studies. MATERIALS AND METHODS: We searched PubMed, EMBASE, and Cochrane library by using key words related with the topic in April 2017. The pooled odd ratios (pORs), relative risks (pRRs), or hazard ratios (pHRs) with 95% confidence intervals (CIs) were calculated based on the random-effects model. Also, we performed subgroup meta-analysis by methodological quality, types of cancer, study design, and omega-3 fatty acids. RESULTS: A total of ten observational studies with six case-control and four cohort studies were included in the final meta-analysis. In the meta-analysis of all the studies, dietary intake of total omega-3 fatty acids was not significantly associated with the risk of endometrial and ovarian cancers (pOR/HR, 0.87; 95% CI, 0.73-1.04; I2=67.2%) (highest versus lowest intake). In the subgroup meta-analysis by type of study, there was no significant association between them in cohort studies (pHR, 1.03; 95% CI, 0.63-1.67, I2=81.9%), whereas its reduced risk was observed in case-control studies (pOR, 0.81; 95% CI, 0.67 to 0.98, I2=55.7%). CONCLUSION: The current meta-analysis of observational studies suggests that there is no higher level of evidence to support the protective effect of dietary omega-3 fatty acids on endocrine-related gynecological cancer. Further prospective studies should be conducted to confirm the association.

Effects of Vitamin and Antioxidant Supplements in Prevention of Bladder Cancer: a Meta-Analysis of Randomized Controlled Trials.

This study aimed to investigate the effects of vitamin and antioxidant supplements in the prevention of bladder cancer using a meta-analysis of randomized controlled trials (RCTs). Fourteen RCTs were included in the final analysis. In a fixed-effect meta-analysis, vitamin and antioxidant supplements showed no preventive effect for bladder cancer (relative risk [RR] = 1.04; 95% confidence interval [CI] 0.92-1.17; I² = 39.7%). Also, there was no preventive effect of these supplements in the subgroup meta-analyses by various factors such as type of supplements, type of cancer prevention, methodological quality, providers of supplements, type of control group, and number of participants. Among the subgroup analyses by type of supplements, beta-carotene supplementation alone marginally increased the risk of bladder cancer (RR = 1.44; 95% CI 1.00-2.09; I² = 0.0%; n = 3). The current meta-analysis found that vitamin and antioxidant supplements have no preventive effect against bladder cancer.

Efficacy of Ginseng Supplements on Fatigue and Physical Performance: a Meta-analysis.

We conducted a meta-analysis to investigate the efficacy of ginseng supplements on fatigue reduction and physical performance enhancement as reported by randomized controlled trials (RCTs). RCTs that investigated the efficacy of ginseng supplements on fatigue reduction and physical performance enhancement compared with placebos were included. The main outcome measures were fatigue reduction and physical performance enhancement. Out of 155 articles meeting initial criteria, 12 RCTs involving 630 participants (311 participants in the intervention group and 319 participants in the placebo group) were included in the final analysis. In the fixed-effect meta-analysis of four RCTs, there was a statistically significant efficacy of ginseng supplements on fatigue reduction (standardized mean difference, SMD = 0.34; 95% confidence interval [CI] = 0.16 to 0.52). However, ginseng supplements were not associated with physical performance enhancement in the fixed-effect meta-analysis of eight RCTs (SMD = -0.01; 95% CI = -0.29 to 0.27). We found that there was insufficient clinical evidence to support the use of ginseng supplements on reducing fatigue and enhancing physical performance because only few RCTs with a small sample size have been published so far. Further lager RCTs are required to confirm the efficacy of ginseng supplements on fatigue reduction.

Efficacy of Vitamin C Supplements in Prevention of Cancer: A Meta-Analysis of Randomized Controlled Trials.

BACKGROUND: Previous randomized controlled trials (RCTs) have reported inconsistent findings regarding the association between vitamin C supplementation and the risk of cancer. METHODS: We performed a meta-analysis of RCTs to investigate the efficacy of vitamin C supplements for prevention of cancer. We searched the PubMed, EMBASE, and Cochrane Library databases in November 2014 using common keywords related to vitamin C supplements and cancer. RESULTS: Among 785 articles, a total of seven trials were identified, which included 62,619 participants; 31,326 and 31,293 were randomized to vitamin C supplementation and control or placebo groups, respectively, which were included in the final analysis. A fixed-effects meta-analysis of all seven RCTs revealed no significant association between vitamin C supplementation and cancer (relative risk, 1.00; 95% confidence intervals, 0.95-1.05). Similarly, subgroup meta-analysis by dose of vitamin C administered singly or in combination with other supplements, follow-up period, methodological quality, cancer mortality, gender, smoking status, country, and type of cancer also showed no efficacy of vitamin C supplementation for cancer prevention. CONCLUSION: This meta-analysis shows that there is no evidence to support the use of vitamin C supplements for prevention of cancer.

Caffeine intake from coffee or tea and cognitive disorders: a meta-analysis of observational studies.

BACKGROUND: Observational epidemiological studies such as cross-sectional, case-control, and cohort studies have reported inconsistent findings regarding the association between caffeine intake from coffee or tea and the risk of cognitive disorders such as dementia, Alzheimer's disease, cognitive impairment, and cognitive decline. METHODS: We searched PubMed and EMBASE in September 2014. Three evaluators independently extracted and reviewed articles, based on predetermined selection criteria. RESULTS: Out of 293 articles identified through the search and bibliographies of relevant articles, 20 epidemiological studies from 19 articles, which involved 31,479 participants (8,398 in six cross-sectional studies, 4,601 in five case-control studies, and 19,918 in nine cohort studies), were included in the final analysis. The pooled odds ratio (OR) or relative risk (RR) of caffeine intake from coffee or tea for cognitive disorders (dementia, Alzheimer's disease, cognitive impairment, and cognitive decline) was 0.82 (95% confidence interval [CI], 0.67-1.01, I² = 63.2%) in a random-effects meta-analysis. In the subgroup meta-analysis by caffeine sources, the summary OR or RR of coffee intake was 0.83 (95% CI, 0.70-0.98; I² = 44.8%). However, in the subgroup meta-analysis by study design, the summary estimates (RR or OR) of coffee intake for cognitive disorders were 0.70 (95% CI, 0.50-0.98; I² = 42.0%) for cross-sectional studies, 0.82 (95% CI, 0.55-1.24; I² = 33.4%) for case-control studies, and 0.90 (95% CI, 0.59-1.36; I² = 60.0%) for cohort studies. CONCLUSIONS: This meta-analysis found that caffeine intake from coffee or tea was not associated with the risk of cognitive disorders.

Efficacy of vitamin and antioxidant supplements in prevention of cardiovascular disease: systematic review and meta-analysis of randomised controlled trials.

OBJECTIVE: To assess the efficacy of vitamin and antioxidant supplements in the prevention of cardiovascular diseases. DESIGN: Meta-analysis of randomised controlled trials. DATA SOURCES AND STUDY SELECTION: PubMed, EMBASE, the Cochrane Library, Scopus, CINAHL, and ClinicalTrials.gov searched in June and November 2012. Two authors independently reviewed and selected eligible randomised controlled trials, based on predetermined selection criteria. RESULTS: Out of 2240 articles retrieved from databases and relevant bibliographies, 50 randomised controlled trials with 294,478 participants (156,663 in intervention groups and 137,815 in control groups) were included in the final analyses. In a fixed effect meta-analysis of the 50 trials, supplementation with vitamins and antioxidants was not associated with reductions in the risk of major cardiovascular events (relative risk 1.00, 95% confidence interval 0.98 to 1.02; I(2)=42%). Overall, there was no beneficial effect of these supplements in the subgroup meta-analyses by type of prevention, type of vitamins and antioxidants, type of cardiovascular outcomes, study design, methodological quality, duration of treatment, funding source, provider of supplements, type of control, number of participants in each trial, and supplements given singly or in combination with other supplements. Among the subgroup meta-analyses by type of cardiovascular outcomes, vitamin and antioxidant supplementation was associated with a marginally increased risk of angina pectoris, while low dose vitamin B(6) supplementation was associated with a slightly decreased risk of major cardiovascular events. Those beneficial or harmful effects disappeared in subgroup meta-analysis of high quality randomised controlled trials within each category. Also, even though supplementation with vitamin B(6) was associated with a decreased risk of cardiovascular death in high quality trials, and vitamin E supplementation with a decreased risk of myocardial infarction, those beneficial effects were seen only in randomised controlled trials in which the supplements were supplied by the pharmaceutical industry. CONCLUSION: There is no evidence to support the use of vitamin and antioxidant supplements for prevention of cardiovascular diseases.

Efficacy of Vitamin and Antioxidant Supplements in Prevention of Esophageal Cancer: Meta-analysis of Randomized Controlled Trials.

BACKGROUND: Observational epidemiological studies have shown that higher intakes of vitamins or antioxidants were inversely associated with the risk of esophageal cancer. However, randomized controlled trials (RCTs) have reported no preventive efficacy of vitamin or antioxidant supplements on esophageal cancer. This meta-analysis aimed to investigate the efficacy of vitamin and antioxidant supplements in the prevention of esophageal cancer as reported by RCTs. METHODS: We searched PubMed, EMBASE, and the Cochrane Library in May 2013. Two authors independently reviewed and selected eligible articles based on predetermined selection criteria. RESULTS: Of 171 articles searched from three databases and relevant bibliographies, 10 RCTs were included in the final analyses. In a fixed-effect meta-analysis of 10 trials, there was no efficacy of vitamin and antioxidant supplements in the prevention of esophageal cancer (relative risk [RR], 1.04; 95% confidence interval [CI], 0.86-1.25; I(2)=0.0%). Also, subgroup meta-analyses showed that vitamin and antioxidant supplements had no preventive efficacy on esophageal cancer both in the high risk (RR, 1.04; 95% CI, 0.85-1.28; n=4) and non-high risk (RR, 1.01; 95% CI, 0.65-1.56; n=6) groups for esophageal cancer. Further, subgroup meta-analyses revealed no preventive efficacy on esophageal cancer by type of methodological quality and type of vitamin and antioxidant supplements. CONCLUSIONS: Unlike observational epidemiological studies, this meta-analysis of RCTs suggests that there is no clinical evidence to support the efficacy of vitamin and antioxidant supplements in the prevention of esophageal cancer.

Efficacy of omega-3 fatty acid supplements (eicosapentaenoic acid and docosahexaenoic acid) in the secondary prevention of cardiovascular disease: a meta-analysis of randomized, double-blind, placebo-controlled trials.

BACKGROUND: Although previous randomized, double-blind, placebo-controlled trials reported the efficacy of omega-3 fatty acid supplements in the secondary prevention of cardiovascular disease (CVD), the evidence remains inconclusive. Using a meta-analysis, we investigated the efficacy of eicosapentaenoic acid and docosahexaenoic acid in the secondary prevention of CVD. METHODS: We searched PubMed, EMBASE, and the Cochrane Library in April 2011. Two of us independently reviewed and selected eligible randomized controlled trials. RESULTS: Of 1007 articles retrieved, 14 randomized, double-blind, placebo-controlled trials (involving 20 485 patients with a history of CVD) were included in the final analyses. Supplementation with omega-3 fatty acids did not reduce the risk of overall cardiovascular events (relative risk, 0.99; 95% CI, 0.89-1.09), all-cause mortality, sudden cardiac death, myocardial infarction, congestive heart failure, or transient ischemic attack and stroke. There was a small reduction in cardiovascular death (relative risk, 0.91; 95% CI, 0.84-0.99), which disappeared when we excluded a study with major methodological problems. Furthermore, no significant preventive effect was observed in subgroup analyses by the following: country location, inland or coastal geographic area, history of CVD, concomitant medication use, type of placebo material in the trial, methodological quality of the trial, duration of treatment, dosage of eicosapentaenoic acid or docosahexaenoic acid, or use of fish oil supplementation only as treatment. CONCLUSION: Our meta-analysis showed insufficient evidence of a secondary preventive effect of omega-3 fatty acid supplements against overall cardiovascular events among patients with a history of cardiovascular disease.

Effects of beta-carotene supplements on cancer prevention: meta-analysis of randomized controlled trials.

This meta-analysis aimed to investigate the effects of beta-carotene supplements alone on cancer prevention as reported by randomized controlled trials (RCTs). We searched PubMed, EMBASE, and CENTRAL. Among the 848 articles searched, 6 randomized controlled trials, including 40,544 total participants, 20,290 in beta-carotene supplement groups, and 20,254 in placebo groups, were included in the final analysis. In a meta-analysis of 6 RCTs, beta-carotene supplements had no preventive effect on either cancer incidence [relative risk (RR) = 1.08, 95% confidence interval (CI) = 0.99-1.18] or cancer mortality (RR = 1.00, 95% CI = 0.87-1.15). Similar findings were observed in both primary prevention trials and secondary prevention trials. Subgroup analyses by various factors revealed no preventive effect of beta-carotene supplementation on cancer prevention and that it significantly increased the risk of urothelial cancer, especially bladder cancer (RR = 1.52, 95% CI = 1.03-2.24) and marginally increased the risk of cancer among current smokers (RR = 1.07, 95% CI = 0.99-1.17). The current meta-analysis of RCTs indicated that there is no clinical evidence to support the overall primary or secondary preventive effect of beta-carotene supplements on cancer. The potential effects, either beneficial or harmful, of beta-carotene supplementation on cancer should not be overemphasized.

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

This meta-analysis aimed to investigate the preventive effect of selenium supplements alone on cancer as reported by randomized controlled trials (RCTs). We searched PubMed, EMBASE, and the Cochrane Library in July 2009. Of the 461 articles searched, 8 articles on 9 RCTs, which included 152,538 total participants, 32,110 in antioxidant supplement groups, and 120,428 in placebo groups, were included. In a random-effects meta-analysis of all 9 RCTs, selenium supplementation alone was found to have an overall preventive effect on cancer incidence [relative risk (RR) = 0.76; 95% confidence interval (CI) = 0.58-0.99]. Among subgroup meta-analyses, the preventive effect of selenium supplementation alone on cancer was apparently observed in populations with a low baseline serum selenium level (<125.6 ng/mL) (RR = 0.64; 95% CI = 0.53 to 0.78; I(2) = 45.5%; n = 7) and in high-risk populations for cancer (RR = 0.68; 95% CI = 0.58 to 0.80; I(2) = 41.5%; n = 8). The meta-analysis of randomized controlled trials indicates that there is possible evidence to support the use of selenium supplements alone for cancer prevention in the low baseline serum selenium level population and in the high-risk population for cancer.

Effects of vitamin treatment or supplements with purported antioxidant properties on skin cancer prevention: a meta-analysis of randomized controlled trials.

AIMS: To investigate the effect of vitamin treatment or supplements with purported antioxidant properties on the primary and secondary prevention of skin cancer using a meta-analysis of randomized controlled trials (RCTs). METHODS: We searched PubMed, Embase and the Cochrane Library in June 2009. Among 398 articles searched, 11 articles on 10 RCTs were included in the final analysis. RESULTS: In a fixed-effects meta-analysis of all 10 trials, vitamin treatment or supplements with purported antioxidant properties were found to have no preventive effect on skin cancer [relative risk (RR) = 0.98; 95% confidence interval (CI) = 0.94-1.03]. Similar findings were observed in a subgroup meta-analysis of 10 studies on both primary prevention trials (RR = 0.98; 95% CI = 0.93-1.03) and secondary prevention trials (RR = 0.97; 95% CI = 0.83-1.13). Further, subgroup meta-analyses revealed no preventive effect on cancer by type of antioxidant, type of cancer and the methodological quality of the studies. CONCLUSION: The current meta-analysis of RCTs indicated that there is no clinical evidence to support an overall primary and secondary preventive effect of vitamin treatment or supplements with purported antioxidant properties on skin cancer. The effect of vitamin supplements on skin cancer should not be overemphasized.

Coffee consumption and risk of prostate cancer: a meta-analysis of epidemiological studies.

OBJECTIVE: To evaluate the association between coffee consumption and the risk of prostate cancer. METHODS: We searched PubMed, EMBASE, and the bibliographies of relevant articles in August 2009. Two evaluators independently reviewed and selected articles based on predetermined selection criteria. RESULTS: Twelve epidemiological studies (eight case-control studies and four cohort studies) were included in the final analysis. In a meta-analysis of all included studies, when compared with the lowest level of coffee consumption, the overall relative risk (RR) of prostate cancer for the highest level of coffee consumption was 1.16 (95% confidence interval [CI] 1.01-1.33). In subgroup meta-analyses by study design, there was a significant positive (harmful) association between coffee consumption and prostate cancer risk in seven case-control studies using both crude and adjusted data (RR 1.20, 95% CI 1.02-1.40; and RR 1.21, 95% CI 1.03-1.43, respectively), whereas there was no significant association in four cohort studies using crude or adjusted data (RR 0.97, 95% CI 0.68-1.38; and RR 1.06, 95% CI 0.83-1.35, respectively). CONCLUSION: Given that a cohort study gives a higher level of evidence than a case-control study, there is no evidence to support a harmful effect of coffee consumption on prostate cancer risk. Further prospective cohort studies are required.