האם תוספי מזון מונעים סרטן?

Am J Clin Nutr. 2007 Jan;85(1):308S-313S. Clinical trials AND observational studies to assess the chronic disease benefits AND risks of multivitamin-multimineral supplements. Multivitamin-multimineral (MVM) supplements are widely used in the United States, often in the hope of reducing the risk of cancer, cardiovascular disease, OR other chronic disease. This article assesses the potential of randomized controlled trials AND epidemiologic cohort studies for yielding reliable information on the effects of MVMs on chronic disease. A brief review of the available literature on MVMs in relation to incidence AND mortality rates from prominent cancers AND cardiovascular diseases is also provided along with a discussion of needed research. Specifically, the strengths AND weaknesses of epidemiologic cohort studies AND randomized controlled trials are summarized AND discussed in the context of single-vitamin supplements when both types of studies are available. Recent review articles that include an assessment of MVMs in relation to cancer AND cardiovascular disease are updated to provide a summary of available data. Few randomized controlled trials AND few cohort studies of MVMs that are directly pertinent to cancer OR cardiovascular disease are available. The data are not compelling concerning a role for MVMs in preventing cancer OR cardiovascular disease morbidity OR mortality, although some interesting leads merit further evaluation. Investigators responsible for cohort studies that assessed MVMs should be encouraged to report available data on MVMs AND chronic disease. Depending in part on the results of such additional reports, a full-scale randomized controlled trial of well-selected MVMs in women may be warranted on public health grounds. 1: J Natl Cancer Inst. 2007 Jan 17;99(2):137-46. Chemoprevention of precancerous gastric lesions with antioxidant vitamin supplementation: a randomized trial in a high-risk population. , BACKGROUND: Gastric cancer is one of the most common malignancies worldwide. Histopathologic studies have identified a sequence of changes in the gastric mucosa that mark the slow progression from normal tissue to carcinoma. Epidemiologic evidence suggests that a diet rich in fresh fruit AND vegetables could be a protective factor against this disease. This effect may be mediated through antioxidant vitamins. METHODS: A randomized, double-blind chemoprevention trial was conducted among 1980 subjects in Tachira State, Venezuela (whose population is at high risk for gastric cancer), to determine the effect of dietary supplementation with vitamin C, vitamin E, AND beta-carotene on the progression AND regression of precancerous gastric lesions. Subjects were randomly assigned to receive either a combination of vitamin C (750 mg/day), vitamin E (600 mg/day), AND beta-carotene (18 mg/day) OR placebo for 3 years. Changes in the gastric mucosa were determined by histologic diagnosis based on five biopsies taken from prespecified areas of the stomach at baseline AND annually for 3 years. All biopsies were reviewed by a single expert pathologist. Progression rates (and regression rates) were calculated by comparing the first AND last available gastroscopies for each subject AND dividing the number of subjects whose diagnoses increased (decreased) in severity by the total follow-up time. Overall rate ratios were calculated by Poisson regression, controlling for baseline diagnosis. All statistical tests were two-sided. RESULTS: Median plasma vitamin levels were increased in the treatment group between baseline AND 1 year after randomization from 0.43 micromol/L (interquartile range [IQR] = 0.26-0.69) to 2.89 micromol/L (IQR = 1.76-4.22) for beta-carotene, from 26.7 micromol/L (IQR = 23.1-31.2) to 54.9 micromol/L (IQR = 42.8-67.6) for alpha-tocopherol, AND from 47.70 micromol/L (IQR = 36.9-58.5) to 61.9 micromol/L (IQR = 52.2-72.7) for vitamin C. Overall progression rates per 100 person-years were 74.3 in the placebo group AND 67.8 in the group randomly assigned to vitamins. Overall regression rates were 109.4 in the placebo group AND 116.5 in the group randomly assigned to vitamins. There was no statistically significant difference in progression rate (rate ratio = 0.92, 95% confidence interval [CI] = 0.74 to 1.15) OR regression rate (rate ratio = 1.09, 95% CI = 0.90 to 1.33) between vitamin AND placebo groups. CONCLUSION: Supplementation with antioxidant micronutrients is not an effective tool for gastric cancer control in this high-risk population. The results of this trial are consistent with previous findings on the lack of effect of nutritional supplementation on precancerous gastric lesions. 1: Int J Cancer. 2006 Dec 12; Prospective study of vitamins C, E, AND A AND carotenoids AND risk of oral premalignant lesions in men. Case-control studies indicate that vitamins C, E, A AND carotenoids decrease risk of oral premalignant lesions (OPLs) AND oral cancer, but clinical trials have failed to find protective effects of beta-carotene AND suggest that vitamin E may increase risk. The authors prospectively evaluated the association between intake of vitamins C, E, A AND carotenoids AND incidence of OPL. Participants were 42,340 men in the Health Professionals Follow-up Study who provided information on supplement use AND diet every 2-4 years by food frequency questionnaire. The authors confirmed 207 clinically OR histopathologically diagnosed OPL events occurring between 1986 AND 2002 by medical record review. Multivariate-adjusted relative risks (RR) of OPL were calculated with proportional hazards models. Total intake of vitamin C, vitamin A OR carotenoids was not significantly associated with OPL risk. Dietary vitamin C was significantly associated with reduced risk (quintile 5 vs. 1, RR = 0.52, 95% CI 0.31-0.85, p(trend) = 0.04), but no association with supplemental vitamin C was observed. Inverse associations were apparent for beta-cryptoxanthin AND alpha-carotene intake. No clear relationship emerged with beta-carotene, lycopene OR lutein/zeaxanthin. Vitamin E was associated with increased risk (quintile 5 vs. 1, RR = 1.86, 95% CI 1.06-3.19), particularly among current smokers AND with supplemental intake (current-smokers, supplement dose tertile 3 vs. 1, RR = 3.07, 95% CI 1.28-7.34, p(trend) = 0.01). For current smokers, beta-carotene also increased risk. Vitamin C from dietary sources, but not supplements, was associated with a reduced risk of OPL. The observed increased risk for current smokers with high vitamin E OR beta-carotene intake should be explored further.