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Epidemiology and Surveillance Research Department, American Cancer Society, Atlanta, GA
Requests for reprints: Carmen Rodriguez, Department of Epidemiology, American Cancer Society, 1599 Clifton Road NE, Atlanta, GA 30329-4250. Phone: (404) 329-7796; Fax: (404) 327-6450. E-mail: crodrigu{at}cancer.org
| Abstract |
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-tocopherol (a form of vitamin E) was associated with decreased risk of prostate cancer in a randomized trial among Finnish smokers. We examined the association between vitamin E supplement use and prostate cancer incidence in the Cancer Prevention Study II Nutrition Cohort. Participants in the study completed a detailed questionnaire at enrollment in 19921993. Historical information was also available from a questionnaire completed in 1982 at enrollment in a previous cohort. Through August 31, 1999, we documented 4,281 cases of incident prostate cancer among 72,704 men. Multivariate-adjusted rate ratios (RRs) were calculated using Cox Proportional Hazards models. Regular vitamin E supplement use (
4 times per week) was not associated with overall risk of prostate cancer or with risk of advanced prostate cancer at diagnosis. No trend was seen with increasing dose of vitamin E. Men who reported regular vitamin E use in both 1982 and in 19921993 were not at lower risk of prostate cancer. Among current smokers, there was a suggestion of slightly reduced risk with regular vitamin E supplement use [RR = 0.87, 95% confidence interval (CI) = 0.671.11]. Our results do not support an important role for vitamin E supplements in prostate cancer prevention.
Key Words: prostate cancer vitamin E prospective cohort
| Introduction |
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-tocopherol), for up to 8 years in the Alpha-Tocopherol and Beta-Carotene Cancer Prevention Study (ATBC Study) (1). The reduction in prostate cancer incidence and mortality was unexpected and prompted the Selenium and Vitamin E Cancer Prevention Trial (SELECT) sponsored by the National Cancer Institute (2). The ongoing SELECT trial will examine the independent and joint effects of selenium and vitamin E (
-tocopherol) supplementation in 32,000 men over more than 12 years. However, results from the SELECT trial will not be available for many years.
Vitamin E is a potent antioxidant and has been hypothesized to decrease cancer risk (3). In diet, vitamin E occurs in several different forms, including both
-tocopherol and
-tocopherol (4). Although
-tocopherol plasma levels were associated with reduced prostate cancer risk in two prospective studies (5, 6), results from two population-based prospective studies raised the possibility that only plasma
-tocopherol is associated with prostate cancer risk (7, 8). Because the high doses of
-tocopherol present in vitamin E supplements can reduce
-tocopherol concentrations in plasma (9), it has been hypothesized that vitamin E supplement use could actually increase prostate cancer risk (10). This hypothesis is supported by the significantly increased risk of prostate cancer associated with vitamin E supplement use observed among never smokers in a recent cohort study (11).
We examined the association between vitamin E supplement use and prostate cancer incidence in a large prospective cohort of elderly men.
| Materials and Methods |
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Participants were 5074 years of age at enrollment in 1992 or 1993, when they completed a self-given mailed questionnaire. Follow-up questionnaires were sent in September 1997 and 1999 to ascertain newly diagnosed cancers. For living cohort members, the response rate was close to 91% for both questionnaires.
We excluded from this analysis men who were lost to follow-up from enrollment through August 31, 1999, who reported any prevalent cancer (except non-melanoma skin cancer) at enrollment or whose self-report of prostate cancer could not be confirmed, and men with incomplete information on vitamin E use (N = 13,700). The analytic cohort consisted of 72,704 men.
Identification of Cases of Prostate Cancer
We identified and verified 4,281 incident cases of fatal or non-fatal prostate cancer that occurred between enrollment and August 31, 1999. Prostate cancer cases were identified through a self-report of cancer on the two follow-up questionnaires (N = 4,154) and verified by medical records (N = 3,304), from linkage with state cancer registries (N = 850), or identified if recorded as the underlying cause of death on a death certificate during follow-up through August 31, 1999 (N = 127). Deaths were ascertained among cohort members through linkage with the National Death Index (13).
For analysis of advanced prostate cancer, we included prostate cancer cases verified by medical records as stages C and D according to the Whitmore-Jewett staging system, those classified as regional or distant by a state cancer registry, and prostate cancer deaths. A total of 668 advanced cases was included in the analysis of advanced cases.
Supplemental Vitamin E Intake Assessment
Supplemental vitamin E intake at enrollment in 19921993 was ascertained using a semiquantitative 68-item food frequency questionnaire (FFQ). The FFQ, a modification of the brief "Health Habits and History Questionnaire" (HHHQ) (14, 15), asked to report the number of vitamin E tablets taken per week during the last year. Response categories were 13 per week, 46 per week, 1 per day, 2 per day, 3 per day, 4 per day, or 5 or more per day. Information about dose was also collected for vitamin E tablets in IUs (100 IU, 200 IU, 400 IU, 1000 IU, don't know). A total of 1,073 men out of the 12,099 reporting individual vitamin E supplement use did not report dose and were assigned a dose of 400 IU, the most common individual vitamin E supplement dose reported. Total supplemental vitamin E intake includes contributions from both individual vitamin E supplements and multivitamin pills. Daily vitamin E supplement dose was estimated from the FFQ using the Diet Analysis System version 3.8a (15), which estimates the vitamin E content of multivitamins as 31 IU per pill. Dietary intake of
-tocopherol in the U.S. is considerably lower, averaging about 15 IU per day (4).
Long-term vitamin E supplement use was assessed through historical information obtained in the 1982 CPS-II questionnaire. This questionnaire included a section asking about current use of four supplements (multivitamins, vitamin A, vitamin C, and vitamin E). For each supplement, participants were asked to report the number of times used in the last month and the number of years of use.
Supplemental vitamin E intake at baseline was examined by frequency and dose based on responses to the 19921993 questionnaire. We classified men by frequency of use as never vitamin E supplement users, occasional users (men who reported taking one to three multivitamin pills or vitamin E tablets per week), or regular users (men who reported taking four or more multivitamin pills or vitamin E tablets per week). Among regular users, daily supplement use was common, with 83% of men reporting daily use of vitamin E supplements (from multivitamin or individual supplements).
Daily dose of vitamin E from supplements (individual supplements and multivitamins combined) was categorized into four categories of IUs (None, 31 IU, 32 to <400 IU,
400 IU). The category of 31 IU per day represents predominantly men who use multivitamins but not individual vitamin E supplements. An intake of 400 or more IU represents at least daily use of an individual vitamin E supplement at the most commonly reported dose (400 IU). Long-term vitamin E supplement use was examined by combining information from the 1982 and 1992 questionnaires. For these analyses, men who in 1982 reported multivitamin or individual vitamin E use 16 or more times per month (roughly equivalent to 4 times per week) and regular use of vitamin E supplements in 1992 were categorized as regular users; those who reported no use of vitamin E supplements in either 1982 or 1992 were classified as never users, and those who reported unquantified "occasional" use, or intake 115 times per month in 1982 and/or in 1992 were categorized as occasional users. We repeated all the analyses both including and excluding men who reported multivitamin use.
Statistical Analysis
We used Cox proportional hazards modeling to examine the association of supplemental vitamin E intake with prostate cancer incidence while adjusting for other potential risk factors. All Cox models were adjusted for age (single year of age at enrollment) and race (white, black, other) by stratification within the model (16). Multivariate models also included variables adjusting for education, family history of prostate cancer in a brother and/or father, smoking, body mass index (BMI) (kg/m2), and quintiles of total energy intake, energy adjusted total fat intake, lycopene, and total (dietary plus supplements) calcium intake. All covariates except age, were modeled as dummy variables using categories shown in Table 1.
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-tocopherol supplement, we examined the association between both regular vitamin E intake and vitamin E dose (none, 131,
32 IU) and prostate cancer incidence stratified by smoking status (never, current, and former smoker). All interaction P values presented are two-sided P values for heterogeneity of rate ratios (RRs) calculated using the likelihood ratio statistic (17). | Results |
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We found no evidence of reduced risk of prostate cancer among men taking vitamin E supplements (from multivitamins or individual vitamin E supplements) regularly in 19921993 [RR = 1.00, 95% confidence interval (CI) = 0.931.07]. Similarly, no reduced risk was seen for prostate cancer cases that were advanced at diagnosis (RR = 0.98, 95% CI = 0.831.16) (Table 2). No dose-response with increasing vitamin E supplement intake was observed (Table 2). Results were similar when men taking multivitamins were excluded (data not shown). Long-term vitamin E supplement use was not associated with risk of overall incident prostate cancer or with risk of advanced prostate cancer (Table 2). In addition, no association was seen when men taking multivitamins were excluded (data not shown).
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| Discussion |
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Previous observational studies have not shown consistently a lower risk of prostate cancer with vitamin E use (18). Vitamin E supplementation of at least 100 IU/day was not associated with the overall risk of prostate cancer in a prospective study of the Health Professionals cohort (11). Consistent with the Finnish ATBC trial, however, vitamin E supplement use was associated with decreased risk of metastatic or fatal prostate cancer among current smokers or recent (
10 years) quitters (11). One case-control study reported significantly lower risk among men in the highest tertile of total vitamin E intake (diet plus supplements) (19); a second case-control study (20) found slightly lower risk among men taking vitamin E supplements daily, although this association was not statistically significant.
Observational studies of plasma levels of vitamin E and risk of prostate cancer have also produced conflicting results (5, 6, 8, 2125). Four studies reported no association between
-tocopherol and prostate cancer (2225), one found plasma levels of
-tocopherol inversely associated with risk of prostate cancer mortality among smokers (21), and two studies found lower levels of
-tocopherol associated with prostate cancer among smokers (5, 21). High plasma levels of
-tocopherol were associated with a decreased risk of developing prostate cancer in two population-based cohort studies while no associations with plasma levels of
-tocopherol were observed (7, 8).
Our results may be compatible with a small reduction in risk of prostate cancer among smokers who regularly use vitamin E (RR = 0.87, 95% CI = 0.671.11). Our study lacks the statistical power to examine the association between vitamin E use and advanced prostate cancer among smokers. Such a selective effect on advanced cancer among smokers is supported by results from the ATBC trial (1), conducted among smokers, where reduced risk with
-tocopherol supplementation was limited to prostate cancers stages II to IV.
In summary, results from this study do not support a strong role of vitamin E in prostate cancer prevention, although a modest protective effect among smokers cannot be ruled out.
| Footnotes |
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Received 8/22/03; revised 11/ 6/03; accepted 11/18/03.
| References |
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-tocopherol, selenium, and subsequent prostate cancer. J Natl Cancer Inst, 2000;92:201823.
-Tocopherol: a new player in prostate cancer prevention? J Natl Cancer Inst, 2000;92:19667.This article has been cited by other articles:
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D. Kang, K.-M. Lee, S. K. Park, S. I. Berndt, U. Peters, D. Reding, N. Chatterjee, R. Welch, S. Chanock, W.-Y. Huang, et al. Functional Variant of Manganese Superoxide Dismutase (SOD2 V16A) Polymorphism Is Associated with Prostate Cancer Risk in the Prostate, Lung, Colorectal, and Ovarian Cancer Study Cancer Epidemiol. Biomarkers Prev., August 1, 2007; 16(8): 1581 - 1586. [Abstract] [Full Text] [PDF] |
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M. E. Wright, S. J. Weinstein, K. A. Lawson, D. Albanes, A. F. Subar, L. B. Dixon, T. Mouw, A. Schatzkin, and M. F. Leitzmann Supplemental and Dietary Vitamin E Intakes and Risk of Prostate Cancer in a Large Prospective Study Cancer Epidemiol. Biomarkers Prev., June 1, 2007; 16(6): 1128 - 1135. [Abstract] [Full Text] [PDF] |
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S. J. Weinstein, M. E. Wright, K. A. Lawson, K. Snyder, S. Mannisto, P. R. Taylor, J. Virtamo, and D. Albanes Serum and Dietary Vitamin E in Relation to Prostate Cancer Risk Cancer Epidemiol. Biomarkers Prev., June 1, 2007; 16(6): 1253 - 1259. [Abstract] [Full Text] [PDF] |
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L. H. Kushi, T. Byers, C. Doyle, E. V. Bandera, M. McCullough, T. Gansler, K. S. Andrews, M. J. Thun, and The American Cancer Society 2006 Nutrition and Phy American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention: Reducing the Risk of Cancer With Healthy Food Choices and Physical Activity CA Cancer J Clin, September 1, 2006; 56(5): 254 - 281. [Abstract] [Full Text] [PDF] |
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J. Limpens, F. H. Schroder, C. M. A. de Ridder, C. A. Bolder, M. F. Wildhagen, U. C. Obermuller-Jevic, K. Kramer, and W. M. van Weerden Combined Lycopene and Vitamin E Treatment Suppresses the Growth of PC-346C Human Prostate Cancer Cells in Nude Mice J. Nutr., May 1, 2006; 136(5): 1287 - 1293. [Abstract] [Full Text] [PDF] |
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I-M. Lee, J. M. Gaziano, and J. E. Buring Vitamin E in the prevention of prostate cancer: where are we today? J Natl Cancer Inst, February 15, 2006; 98(4): 225 - 227. [Full Text] [PDF] |
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V. A. Kirsh, R. B. Hayes, S. T. Mayne, N. Chatterjee, A. F. Subar, L. B. Dixon, D. Albanes, G. L. Andriole, D. A. Urban, and U. Peters Supplemental and dietary vitamin E, beta-carotene, and vitamin C intakes and prostate cancer risk. J Natl Cancer Inst, February 15, 2006; 98(4): 245 - 254. [Abstract] [Full Text] [PDF] |
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J. M. Chan, P. H. Gann, and E. L. Giovannucci Role of Diet in Prostate Cancer Development and Progression J. Clin. Oncol., November 10, 2005; 23(32): 8152 - 8160. [Abstract] [Full Text] [PDF] |
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