European Journal of Cardiovascular Prevention & Rehabilitation

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1 European Journal of Cardiovascular Prevention & Rehabilitation Antioxidant vitamins intake and the risk of coronary heart disease: meta-analysis of cohort studies Zheng Ye and Honglin Song European Journal of Cardiovascular Prevention & Rehabilitation : 26 DOI: /HJR.0b013e3282f11f95 The online version of this article can be found at: Published by: On behalf of: European Society of Cardiology European Association for Cardiovascular Prevention and Rehabilitation Additional services and information for European Journal of Cardiovascular Prevention & Rehabilitation can be found at: Alerts: Subscriptions: Reprints: Permissions: >> Version of Record - Feb 1, 2008 What is This? Downloaded from cpr.sagepub.com at University Library Utrecht on October 27, 2014

2 Original Scientific Paper Antioxidant vitamins intake and the risk of coronary heart disease: meta-analysis of cohort studies Zheng Ye a and Honglin Song b Departments of a Public Health and Primary Care and b Oncology, Strangeways Research Laboratory, University of Cambridge, Cambridge, UK Received 6 December 2006 Accepted 14 August 2007 Background Many epidemiological studies have reported that antioxidant vitamin intake from diet or supplements are associated with a lower risk of coronary heart disease (CHD), the findings are, however, inconsistent. We undertook a metaanalysis of cohort studies to examine the relations between antioxidant vitamins (vitamins C, E, and b-carotene) and CHD risk. Methods and results We included all the relevant cohort studies if they provided a relative risk and corresponding 95% confidence interval (CI) of CHD in relation to antioxidant vitamins intake from diet or supplement. Fifteen cohort studies were identified involving a total of 7415 incident CHD cases and participants with a median follow-up of approximately 10, 8.5, and 15 years for vitamins C, E, and b-carotene, respectively. Pooled estimates across studies were obtained by random-effects model. The potential sources of heterogeneity and publication bias were also estimated. For vitamins C, E, and b-carotene, a comparison of individuals in the top third with those in the bottom third of baseline value yielded a combined relative risk of 0.84 (95% CI, ), 0.76 (95% CI, ), and 0.78 (95% CI, ), respectively. Subgroup analyses show that dietary intake of vitamins C and E and supplement use of vitamin E have an inverse association with CHD risk, but supplement use of vitamin C has no significant association with CHD risk. In the dose response meta-analysis, each 30 mg/day increase in vitamin C, 30 IU/day increase in vitamin E, and 1 mg/day increase in b-carotene yielded the estimated overall relative risk for CHD of 1.01 (95% CI, ), 0.96 (95% CI, ), and 1.00 (95% CI, ), respectively. Conclusions Our findings in this meta-analysis suggest that an increase in dietary intake of antioxidant vitamins has encouraging prospects for possible CHD prevention. Eur J Cardiovasc Prev Rehabil 15:26 34 c 2008 The European Society of Cardiology European Journal of Cardiovascular Prevention and Rehabilitation 2008, 15:26 34 Keywords: antioxidant vitamin, coronary heart disease, cohort studies, meta-analysis Introduction Many prospective epidemiological studies have reported that consumption of fruit and vegetables, which are abundant in antioxidant vitamins, is associated with reduced risk of cardiovascular diseases [1 6]. The role of such antioxidant vitamins (including vitamins C, E, and b-carotene) in prevention and treatment of coronary heart disease (CHD) has been a subject of intensive investigation over the past several decades [7 10]. Substantial interest on this topic was stimulated initially Correspondence to Dr Zheng Ye, PhD, Department of Public Health and Primary Care, University of Cambridge, Strangeways Site, Cambridge CB1 8RN, UK Tel: ; fax: ; zy215@medschl.cam.ac.uk c 2008 The European Society of Cardiology by the findings in the preclinical settings that antioxidant vitamins can help scavenge highly reactive free radicals and inhibit lipid peroxidation, and thus may slow down or prevent the development of atherosclerosis [11,12]. While some prospective studies support this antioxidant hypothesis that antioxidant vitamins intake from diet or supplement are associated with a lower risk of CHD, the findings are somewhat inconsistent [13 27]. Results from these studies are particularly difficult to interpret as some studies typically involve only a few hundred CHD cases, which may be too few to characterize reliably the magnitude of any association between antioxidant vitamins intake and CHD risk. A recent meta-analysis of randomized trials failed to demonstrate a beneficial effect

3 Antioxidant vitamins, CHD Ye and Song 27 of antioxidant vitamins (vitamin E and b-carotene) supplement on the morbidity and mortality of cardiovascular disease [28], and this disparity between the results of prospective cohort studies and clinical trials might reflect some general differences between the sample sizes, doses of supplement, duration of follow-up, study design, health behaviors, and dietary habits [8,9]. Despite much uncertainty existing about the relation between antioxidant vitamins intake from diet or supplement and the risk of CHD, it is of great public interest as millions of people worldwide take daily doses of vitamins C and E and b-carotene, partly encouraged by their physicians [29,30] based upon the findings of these conflicting and inconclusive results. This situation possibly also confuses consumers about the best way to support their cardiac health and highlights the need for systematic review of the existent evidences. A previous attempt to synthesize available data has pooled individual data from nine studies of antioxidant vitamins prior to 1996 [31]. Since then, several large cohort studies have been published, which have not been included in the previous pooled analysis. In order to quantitatively evaluate such association more reliably, a meta-analysis of prospective cohort studies was undertaken to summarize the epidemiological evidence for the use of antioxidant vitamins in CHD, and to identify potential sources of study variation. Methods Long-term prospective cohort studies published before May 2007 that reported on association between antioxidant vitamins (e.g. vitamins C, E, and b-carotene) and first incident CHD [e.g. nonfatal myocardial infarction (MI) or CHD death] were sought by MEDLINE searches, scanning of relevant reference lists, and review articles. Computer searches used combination of key words relating to the relevant antioxidant vitamins (e.g. vitamin C, vitamin E, b-carotene, and beta-carotene ) in combination with words related to CHD (e.g. coronary heart disease or coronary artery disease or myocardial infarction, or ischemic heart disease ). All the relevant studies were included if they provided a relative risk and corresponding 95% confidence interval (CI) of CHD in relation to antioxidant vitamins intake from diet or supplement. For each contributing study, the following information was abstracted: the name of cohort, year of publication, geographical location, population resource and sample method, gender, years of enrolment, number of incidence cases, number of participants, participants age range, approximate duration of follow-up, median intake of vitamin levels, and adjustment for potential confounders. Adjustment as shown in the figures is denoted as + for age; only; + + for age plus smoking; for age; smoking plus some other standard vascular risk factors; for all plus socioeconomic factors. Different studies have used a variety of different cut-off levels in analyses of antioxidant vitamins intake and CHD risk [such as microgram (mg), IU per days, mg per day, binary, tertile, quartile, and quintile], and a range of antioxidant vitamins use varied across studies. Therefore, to ensure a consistent approach to analysis in this review, the report point-estimate for each study was standardized using methods described previously [32]. Briefly, the log ratio of the risk of disease among individuals in the top third versus those in the bottom third of baseline measurement of the relevant factor was estimated from the published report, assuming a log-linear association with disease risk over the mid range of baseline values of antioxidant vitamins. For the dose response relationship, a weighted linear regression was used to model the log relative risk for CHD as a linear function of vitamins intake. The common regression slope and 95% CI were calculated by combining the individual log relative risk of each category from the individual studies weighed by the inverse of the variance. For each study, the median intake of antioxidant vitamins for each category was used. When the median intake per category was not presented in the report, the midpoint of the upper and lower boundaries in each category was used. If upper boundary of the highest category was not provided, the same scale of vitamins intake as the preceding category was assigned. When the lowest category was open-ended, the lowest category was assumed to be zero. The results variously reported as hazard ratio and mortality ratio were assumed to approximate the same measure of relative risk. Pooled estimates across studies were obtained by random effect summary measures of the reported log-risk ratios weighed by the inverse of the variance. Heterogeneity was assessed using the I 2 statistic, which describes the proportion of variation in the log-relative risks that is attributable to genuine differences across studies rather than to random error [33], a w 2 test [34], and by using random-effects regression models with restricted maximum likelihood estimation. Study size ( Z 500 cases versus < 500 cases), location (USA versus Europe), sex (male versus female), duration of follow-up ( < 10 years versus Z 10 years), population source (population registers versus occupational register), and vitamins intake (dietary intake versus supplement use) were prespecified as characteristics for assessment of heterogeneity; other potentially relevant subgroup analyses (such as age) could not reliably be investigated because individual participant data were not available in this meta-analysis. Publication bias was assessed using funnel plots (so-called because, in the absence of publication bias, such plots resemble symmetrical inverted funnels), and Egger s regression test [35]. Statistical analyses were done using Stata (version 8.0) statistical software (Stata Corporation, College Station, Texas, USA). In the figures, areas of squares of individual studies are inversely proportional to the variances of the

4 28 European Journal of Cardiovascular Prevention and Rehabilitation 2008, Vol 15 No 1 log-relative risks, and the horizontal lines represent 95% CIs. Studies in the figures are listed in descending order of study size. Results A total of 15 cohort studies were identified involving a total of 7415 incident CHD cases and participants. A list of the relevant details abstracted from these studies is provided in Table 1. Of these 15 studies, 14 studies reported on vitamin C (a total of 6863 incident CHD cases during a median follow-up of approximately 10 years), nine studies reported on vitamin E (a total of 4017 incident CHD cases during a median follow-up of approximately 8.5 years), and three studies reported on b-carotene (a total of 733 incident CHD cases during a median follow-up of approximately 15 years). Eleven cohort studies are from USA and four from Europe; most of the studies used a rather than a random sampling method, and involved middle-aged participants at the baseline survey. A moderately high degree of heterogeneity was found among the 14 studies of vitamin C intake and CHD risk (I 2 = 63; 95% CI, 36 79, P = ). Little of this heterogeneity, however, was explained by the study characteristics such as number of cases, sex, geographical location, and duration of follow-up (all P > 0.05). Overall, comparison of individuals with vitamin C intake in the top third with those in the bottom third at baseline yielded a combined relative risk of 0.84 for CHD (95% CI, ; Fig. 1). Subsidiary analyses of vitamin C intake showed consistency in the direction of effect when studies were grouped by the study characteristics described in Fig. 2. Compared with individuals in the lowest intake of vitamin C, those in the highest intake had a significantly reduced risk of CHD, regardless of study size, location, and population source (Fig. 2). When the associations between vitamin C intake from diet and supplement and CHD risk were considered separately, comparison of individuals with dietary intake and supplement use in the top third with those in the bottom third at baseline yielded a combined relative risk of 0.86 for CHD (95% CI, ) and 0.87 (95% CI, ) for CHD, respectively (Fig. 2). In the dose response meta-analysis, nine cohort studies have data on each category of vitamin C intake. The estimated overall relative risk of CHD for an increase in vitamin C intake of 30 mg/day was 1.01 (95% CI, ; Fig. 3). Marginal evidence of heterogeneity was found among the studies of vitamin E intake and CHD risk (I 2 = 42; 95% CI, 0 72, P = 0.08). Overall, comparison of individuals with vitamin E intake in the top third with those in the bottom third at baseline yielded a combined relative risk of 0.76 for CHD (95% CI, ; Fig. 4). Subsidiary analyses of vitamin E intake showed very high consistency in the direction of effect when studies were grouped by the characteristics described in Fig. 2. Compared with individuals in the lowest intake of vitamin E, those in the highest intake had a significantly reduced risk of CHD, irrespective of study size, sex, duration of follow-up, and type of vitamins intake (Fig. 2). When the associations between vitamin E intake from diet and supplement and CHD risk were considered separately, comparison of individuals with dietary intake and supplement use in the top third with those in the bottom third at baseline yielded a combined relative risk of 0.78 for CHD (95% CI, ) and 0.78 (95% CI, ) for CHD, respectively (Fig. 2). In the dose response meta-analysis, four cohort studies have data on each category of vitamin E intake. The estimated overall relative risk of CHD for an increase in vitamin E intake of 30 IU/day (20 mg/day) was 0.96 (95% CI, ; Fig. 3). Marginal evidence of heterogeneity was found among the studies of b-carotene intake and CHD risk (I 2 = 64; 95% CI, 0 90, P = 0.06). Overall, comparison of individuals with b-carotene intake in the top third with those in the bottom third at baseline yielded a combined relative risk of 0.78 for CHD (95% CI, ; Fig. 4). In the dose response meta-analysis, three cohort studies have data on each category of b- carotene intake. The estimated overall relative risk of CHD for an increase in b-caroteneintakeof1mg/daywas1.0 (95% CI, ; Fig. 3). The funnel plot did not indicate the presence of publication bias in the antioxidant vitamins C, E, and b-carotene reviewed (Fig. 5). Discussion The present meta-analysis involves data on antioxidant vitamins intake and CHD risk published in 15 prospective cohort studies, comprising a total of more than 7000 incident CHD cases and participants. The review indicates that the relevance of the weakly inverse overall association observed for vitamin C and b-carotene intake with the risk of CHD is uncertain, particularly given nonsignificant association observed in the dose response meta-analysis. The present meta-analysis also indicates the existence of a moderately inverse relation between vitamin E intake and the risk of CHD. An increment of 30 IU/day of vitamin E intake could possibly lower CHD risk by 4%. Subgroup analyses show that dietary intake of vitamins C and E and supplement use of antioxidant vitamin E have an inverse association with CHD risk, but supplement use of vitamin C shows no significant association with the risk of CHD. The present meta-analysis has several strengths. In contrast with retrospective studies, long-term prospective cohort studies include individuals who remain diseasefree before the diagnosis of CHD. Therefore, assessment of the cohort studies in the present meta-analysis should largely reduce the scope for selection bias and recall bias. Most of studies included in the present review have a large sample size and a long duration of follow-up. These large studies combined should be less prone to selective

5 Table 1 Characteristics of 15 prospective studies of antioxidant vitamin intake and coronary heart disease in essentially general populations Median intake Cohort Location Population source/ Sample Methods a Time of baseline survey Gender Age (years) Follow-up (years) No. of CHD events Total cohort b Vitamin C (mg/day) Vitamin E (IU/day) b-carotene (mg/day) Adjustment NHS [13] USA Female nurse/ NHEFS c [14] USA Population register/ Caerphilly UK Resident men/ [15] NHS [27] USA Female nurse/ MHP [25] USA Male health professionals/ LPS [19] Finland Population register/ random WES [24] USA Occupational/ random DHSSNS [16] UK Population register/ random IWHS [20] USA Female health professionals/ NSS [26] USA Household listings/ EPESE [21] USA Household listings/ Rotterdam [18] Netherlands Household listings/ PHS [18] USA Occupational/ random NHS update [23] USA Female nurse/ 1980 F NR Age, smoking, and other CHD risk factors M/F NR No M (diet) Age and smoking 1980 F (suppl); 4.4 (diet) 1986 M (both) 11.2 (both) Age and smoking Age, smoking, BMI, total calories, dietary fiber, alcohol, reported hypertension, aspirin use, physical activity, parental history of MI, and profession M/F NR NR Age, smoking, serum cholesterol, BMI, and energy intake M (diet) 3.5 (diet) Age, smoking, blood pressure, BMI, serum cholesterol, family history of cardiovascular disease, alcohol consumption, energy, iron, saturated fatty acids, and polyunsaturated fatty acids M/F > (diet) Age and sex 1986 F (diet); (suppl) 6.9 (diet); 63 (suppl) Age, smoking, BMI, energy intake, waist-to-hip, diabetes mellitus, oral-contraceptive use, estrogen-replacement therapy, physical activity, alcohol intake, martial status, and level of educational attainment Age, sex, disease status, and disabilities affecting shopping M/F (both) 18.9 mg/ day (both) M/F NR NR Age, sex, smoking, aspirin use, alcohol consumption, BMI, history of coronary disease, education, and race 1996 M/F (diet) 12.2 mg/ day (diet) 1.4 (diet) Age, sex, smoking, alcohol intake, antioxidative vitamin intake, and energy intake 1982 M NR NR Smoking, alcohol intake, BMI, physical activity, history hypertension, and history of hypercholesterolemia 1980 F NS (diet); 155 Age, smoking, BMI, postmenopausal hormone use, (suppl) parental history of MI, history of high blood pressure, history of high cholesterol, diabetes, exercise, aspirin use, alcohol intake, total caloric intake, saturated fat intake, and polyunsaturated fat intake 1974 M/F (diet) 7 mg/day 1.7 (diet) Age, smoking, BMI, cholesterol, and energy (diet) WCS c [17] USA Household listings/ Total a Random sampling method involved invitation of randomly selected subgroup of eligible persons. Complete sampling involved invitation of all eligible persons. F: female; M: male; NR: data available but not reported. b This refers to the number of people in whom antioxidant vitamins intake were assessed. c This outcome includes all cardiovascular deaths (heart attack and stroke). NHS, Nurses Health Study; NHEFS, National Health and Nutrition Examination Survey (NHANES) Epidemiologic Follow-up Study; MHP, Health Professionals; LPS, Longitudinal Population Study; WES, Western Electric Study; DHSSNS, Department of Health and Social Security Nutritional Survey; IWHS, Iowa Women Health Study; EPESE, Established Populations for Epidemiologic Studies of the Elderly; PHS, Physicians Health Study; WCS, Washington County Study. Antioxidant vitamins, CHD Ye and Song 29

6 30 European Journal of Cardiovascular Prevention and Rehabilitation 2008, Vol 15 No 1 Fig. 1 Study No. of cases NHS update EPESE NHEFS MHP PHS NHS WCS IWHS WES LPS, M DHSSNS Caerphilly Rotterdam NSS LPS, F Overall 6863 Degree of adjustment Relative risk and 95% CI (top third versus bottom third) 0.84 (0.73, 0.95) Prospective cohort studies of vitamin C intake and the risk of coronary heart disease publication bias than are the smaller studies, and give more reliable assessment of the relation between antioxidant vitamins and CHD risk. A well designed and careful statistical analysis of prospective cohort studies could provide a useful method to test the antioxidant hypothesis, which might have public health benefits. The potential limitations of the present report that merit consideration are: (i) It was not possible to adjust consistently for possible confounding factors in this meta-analysis of available cohort studies because the present report was based on variable data reported in the published literature. More detailed pooling of these studies, perhaps based on the individual participant data, is required to help the assessment of any independent associations and to investigate the impact of antioxidant vitamins on CHD risk in different circumstances (such as different ages, and at different levels of established risk factors). (ii) In the present review, our analyses were based upon observational studies. The inherent limitations of such studies could bias our findings. The possibility of residual confounding or measurement errors could not be ruled out. (iii) Despite no publication bias examined in the present meta-analysis, it is still difficult to exclude such bias in the studies because authors and editors maybe more likely to publish significant findings than nonsignificant ones. Some epidemiological studies with weak or null effects for this association may have failed to be published. (iv) Recent evidence has showed that analysis of epidemiological studies of antioxidant vitamins may need to take into account social and behavioral factors [36]. The conflicting findings between prospective and clinical trials are probably the results of residual confounding caused by inadequate adjustment for the socioeconomic factors [36]. Most of the cohort studies included in present report, however, have failed to consider these factors in the statistical adjustments or did not measure such factors, and meta-analysis of such cohort studies might lead to biased results. Although an inverse relation between vitamin E and CHD risk has been observed in the present metaanalysis, the validity and reliability of such relation are still in need of careful consideration. The possibility of other possible confounders cannot be ruled out in the present meta-analysis. For example, people taking antioxidant vitamins regularly are very likely to have other healthy lifestyle habits such as exercise regularly, have a low dietary intake of cholesterol and saturated fat, maintaining a healthy body weight, and be nonsmokers. It is difficult to separate beneficial effects of dietary or supplemental vitamin intake from effects due to healthy lifestyle habits, because such healthy habits, have already been shown to reduce the risk of CHD. We could not rule out the possibility of the inverse relation between vitamin E intake and CHD risk is partially explained by health lifestyle factors not estimated in these studies. Figure 3 indicates that the claimed dose response for vitamin E may be driven by one study [25]. Sensitivity analysis indicates that the inverse relation still persists, with estimated overall relative risk of 0.95 (95% CI, ) after removing this study.

7 Antioxidant vitamins, CHD Ye and Song 31 Fig. 2 Antioxidant Groups No. of cases Relative risk and 95% CI (top third versus bottom third) Vitamin C Vitamin E Study size 500 patients: 6 studies < 500 patients: 9 studies Sex Male: 5 studies Female: 4 studies Duration of follow-up 10 years: 8 studies < 10 years: 7 studies Location North America: 10 studies Europe: 5 studies Population source Population registers: 9 studies Occupational registers: 6 studies Vitamin intake Dietary: 9 studies Supplement: 3 studies Study size 500 patients: 4 studies < 500 patients: 5 studies Sex Male: 3 studies Female: 3 studies Duration of follow-up 10 years: 4 studies < 10 years: 5 studies Location North America: 7 studies Europe: 2 studies Population source Population registers: 5 studies Occupational registers: 4 studies Vitamin intake Dietary: 6 studies Supplement: 4 studies Prospective cohort studies of vitamins C and E intake and the risk of coronary heart disease, grouped by various study characteristics. With regard to the lack of clear beneficial effects of antioxidant vitamins intake on the risk of CHD in many clinical trials [28], several important factors may need to be considered. Most clinical trials were typically conducted among high-risk populations (including known coronary disease) and started in middle age. In contrast, prospective cohort studies often start at younger ages and generally recruit healthy persons. Discrepancy between cohort studies and randomized clinical trial may be partly explained by difference in coronary risk in study participants. This may also imply that antioxidants might be effective only in persons without established diseases [8]. The duration of follow-up in most of clinical trials has generally been limited to 5 years or less. In contrast, the duration of follow-up in many cohort studies are generally sustained for much longer periods (at least 5 years or even decades). This may indicate that the duration in clinical trials might be insufficient to record an effect. Although disparity documented in the antioxidant vitamins C and E from supplement use between cohort studies and clinical trials, the findings in the present meta-analysis indicated an inverse relation between the dietary intake of vitamins C and E and the risk of CHD. The pooled analyses found that those with more dietary intake of vitamins C and E could have a 14 and 22% lower risk of CHD, respectively. It is well known that the major dietary sources of vitamins C and E are plant foods mainly fruits, vegetables, and nuts. Dietary intake of vitamins C and E are highly correlated with fruits, vegetables, and nuts intake [37]. For example, an increase in one serving of fruit and vegetable

8 32 European Journal of Cardiovascular Prevention and Rehabilitation 2008, Vol 15 No 1 Fig Relative risk 1.0 Relative risk Vitamin C (mg/day) Vitamin E (IU/day) Relative risk β-carotene (mg/day) Dose response relation of relative risk of coronary heart disease in relation to vitamins C, E, and b-carotene intake. The area of each data point is proportional to its statistical weight. The solid lines show weighted relative risk on all data points. The upper and lower dashed lines represent the 95% confidence interval (CI) on the mean of the predicted value. Fig. 4 Study Vitamin E EPESE MHP PHS NHS WCS IWHS LPS, M Rotterdam NSS LPS, F WCS WES Rotterdam No. of cases Subtotal 4017 β-carotene Subtotal 733 Degree of adjustment Relative risk and 95% CI (top third versus bottom third) 0.76 (0.63, 0.89) 0.78 (0.53, 1.04) Prospective cohort studies of vitamin E and b-carotene intake and the risk of coronary heart disease. M, male; F, female. was associated with an increase of at least 30 mg daily vitamin C [37]. A recent meta-analysis showed that increased consumption of fruit and vegetable is inversely associated with the risk of CHD [38]. Therefore, accumulating evidences suggest that consumption of a diet high in food sources of antioxidant vitamins, instead

9 Antioxidant vitamins, CHD Ye and Song 33 Fig Begg's funnel plot with pseudo 95% CI 1 Begg's funnel plot with pseudo 95% CI Log relative risk SE of log relative risk Vitamin C SE of log relative risk Vitamin E Begg's funnel plot with pseudo 95% CIs 0.5 Log relative risk SE of log relative risk β-carotene Funnel plot of prospective cohort studies of vitamins C, E, and b-carotene intake and coronary heart disease. of antioxidant supplements, might reduce the risk of CHD. In summary, the present report suggests three major conclusions. First, the present meta-analysis of cohort studies indicated that there was an inverse association between vitamin E intake and CHD risk. Each 30 IU/day increase in vitamin E intake was related to a lower risk of CHD by 4%. The overall inverse associations of vitamin C and b-carotene intake with the risk of CHD are uncertain, particularly given nonsignificant association observed in the dose response meta-analysis. Second, careful statistical adjustment for the lifestyle and socioeconomic factors may be required to fully consider the relations between antioxidant vitamins and CHD in the further investigations. Third, our findings in the present meta-analysis suggest that an increase in dietary intake of foods rich in antioxidant vitamins might have beneficial effects for CHD. Acknowledgement Conflict of interest: none declared. References 1 Rimm EB, Ascherio A, Giovannucci E, Spiegelman D, Stampfer MJ, Willett WC. Vegetable, fruit, and cereal fiber intake and risk of coronary heart disease among men. JAMA 1996; 275: Liu S, Lee IM, Ajani U, Cole SR, Buring JE, Manson JE, Physicians Health Study. Intake of vegetables rich in carotenoids and risk of coronary heart disease in men: the Physicians Health Study. Int J Epidemiol 2001; 30: Joshipura KJ, Hu FB, Manson JE, Stampfer MJ, Rimm EB, Speizer FE, et al. The effect of fruit and vegetable intake on risk for coronary heart disease. Ann Intern Med 2001; 34: Bazzano LA, He J, Ogden LG, Loria CM, Vupputuri S, Myers L, et al. Fruit and vegetable intake and risk of cardiovascular disease in US adults: the first National Health and Nutrition Examination Survey Epidemiologic Follow-up Study. Am J Clin Nutr 2002; 76: Steffen LM, Jacobs DR Jr, Stevens J, Shahar E, Carithers T, Folsom AR. Associations of whole-grain, refined-grain, and fruit and vegetable consumption with risks of all-cause mortality and incident coronary artery disease and ischemic stroke: the Atherosclerosis Risk in Communities (ARIC) Study. Am J Clin Nutr 2003; 78: Dauchet L, Ferrieres J, Arveiler D, Yarnell JW, Gey F, Ducimetiere P, et al. Frequency of fruit and vegetable consumption and coronary heart disease in France and Northern Ireland: the PRIME study. Br J Nutr 2004; 92: Kritharides L, Stocker R. The use of antioxidant supplements in coronary heart disease. Atherosclerosis 2002; 164: Jha P, Flather M, Lonn E, Farkouh M, Yusuf S. The antioxidant vitamins and cardiovascular disease: a critical review of epidemiologic and clinical trial data. Ann Intern Med 1995; 123: Marchioli R, Schweiger C, Levantesi G, Tavazzi L, Valagussa F. Antioxidant vitamins and prevention of cardiovascular disease: epidemiological and clinical trial data. Lipids 2001; 36:S53 S Kris-Etherton PM, Lichtenstein AH, Howard BV, Steinberg D, Witztum JL. Antioxidant vitamin supplements and cardiovascular disease. Circulation 2004; 110: Padayatty SJ, Katz A, Wang Y, Eck P, Kwon O, Lee JH et al. Vitamin C as an antioxidant: evaluation of its role in disease prevention. J Am Col Nutr 2003; 22: Chattopadhyay A, Bandyopadhyay D. Vitamin E in the prevention of ischemic heart disease. Pharm Rep 2006; 58:

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