14 Articles | JNCI Vol. 101, Issue 1 | January 7, 2009
A large number of epidemiologic studies have suggested that a diet
high in fruits, vegetables, and other foods derived from plants is
associated with a lower risk of cancer ( 1 – 8 ). Antioxidant nutrients
such as ascorbic acid, ? -tocopherol, and the carotenoids (eg, beta
carotene) that are present in plant-derived foods may have a major
preventive role against carcinogenesis ( 9 ), and it has been sug-
gested that they may suppress tumor cell growth and induce tumor
cell apoptosis ( 10 – 12 ). Antioxidants also counterbalance the pro-
duction of reactive oxygen species (ROS), which may cause oxida-
tive damage to cells and modify cell growth regulatory pathways,
leading to enhanced risk for carcinogenesis ( 13 – 15 ).
Over the past three decades, numerous clinical trials ( 16 – 30 )
have evaluated the effi cacy of antioxidants and minerals, used sin-
gly or in various combinations, in the prevention of cancers and
other chronic diseases. However, their fi ndings have been incon-
sistent, and results of most of them ( 16 – 27 ) did not support a
benefi t of vitamin or mineral supplements in primary cancer
prevention. Several recent meta-analyses also showed no reduction
in risk for cancer development with antioxidant vitamins or beta
carotene, with the exception of a possible reduction in cancer
Affiliations of authors: Division of Preventive Medicine, Department of
Medicine, Brigham and Women ’ s Hospital and Harvard Medical School,
Boston, MA (JL, NRC, CA, EZ, JMG, MVD, JEB, JAEM); Department of
Epidemiology, Harvard School of Public Health, Boston, MA (NRC, JEB,
JAEM); Cardiovascular Division (CA), Division of Aging (JMG), Department
of Medicine, Brigham and Women’s Hospital; Department of Ambulatory
Care and Prevention, Harvard Medical School, Boston, MA (JEB) .
Correspondence to: Jennifer Lin, PhD, Division of Preventive Medicine,
Department of Medicine, Brigham and Women’s Hospital and Harvard
Medical School, 900 Commonwealth Ave East, Boston, MA 02215 (e-mail:
See “Funding” and “Notes” following “References.”
© The Author 2008. Published by Oxford University Press. All rights reserved.
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Vitamins C and E and Beta Carotene
Supplementation and Cancer Risk: A Randomized
Jennifer Lin , Nancy R. Cook , Christine Albert , Elaine Zaharris , J. Michael Gaziano , Martin Van Denburgh ,
Julie E. Buring , JoAnn E. Manson
Background Observational studies suggested that a diet high in fruits and vegetables, both of which are rich with anti-
oxidants, may prevent cancer development. However, findings from randomized trials of the association
between antioxidant use and cancer risk have been mostly negative.
Methods From 8171 women who were randomly assigned in the Women’s Antioxidant Cardiovascular Study, a
double-blind, placebo-controlled 2 × 2 × 2 factorial trial of vitamin C (500 mg of ascorbic acid daily),
natural-source vitamin E (600 IU of ? -tocopherol every other day), and beta carotene (50 mg every other
day), 7627 women who were free of cancer before random assignment were selected for this study.
Diagnoses and deaths from cancer at a specific site were confirmed by use of hospital reports and the
National Death Index. Cox proportional hazards regression models were used to assess hazard ratios (rep-
resented as relative risks [RRs]) of common cancers associated with use of antioxidants, either individually
or in combination. Subgroup analyses were conducted to determine if duration of use modified the asso-
ciation of supplement use with cancer risk. All statistical tests were two-sided.
Results During an average 9.4 years of treatment, 624 women developed incident invasive cancer and 176 women
died from cancer. There were no statistically significant effects of use of any antioxidant on total cancer inci-
dence. Compared with the placebo group, the RRs were 1.11 (95% confidence interval [CI] = 0.95 to 1.30) in
the vitamin C group, 0.93 (95% CI = 0.79 to 1.09) in the vitamin E group, and 1.00 (95% CI = 0.85 to 1.17) in
the beta carotene group. Similarly, no effects of these antioxidants were observed on cancer mortality.
Compared with the placebo group, the RRs were 1.28 (95% CI = 0.95 to 1.73) in the vitamin C group, 0.87 (95%
CI = 0.65 to 1.17) in the vitamin E group, and 0.84 (95% CI = 0.62 to 1.13) in the beta carotene group. Duration
and combined use of the three antioxidants also had no effect on cancer incidence and cancer death.
Conclusions Supplementation with vitamin C, vitamin E, or beta carotene offers no overall benefits in the primary pre-
vention of total cancer incidence or cancer mortality.
J Natl Cancer Inst 2009;101: 14 – 23
JNCI | Articles 15
mortality with selenium supplementation ( 31 – 35 ). The negative
fi ndings may be attributable to the short exposure to interventions,
with most trials lasting only 4 – 6 years ( 36 ): because malignant
cancer cells can take decades to develop, many trials may have been
too short to demonstrate any benefi t ( 36 ). Another possible expla-
nation is that most trials have evaluated the effects of high doses of
only one or two antioxidants ( 36 – 39 ), although experimental data
have suggested that antioxidants act not only individually but also
cooperatively to achieve optimal effects on cancer prevention.
Moreover, heterogeneity of the study populations may have con-
tributed to the divergence of the fi ndings, with the possibility that
antioxidants could be benefi cial among populations more likely to
experience oxidative stress ( 40 ).
In this randomized factorial trial of an average 9 years of sup-
plementation and follow-up among women at high risk of cardio-
vascular disease, we systematically evaluated the individual and
combined effects of three antioxidant supplements, ascorbic acid,
vitamin E, and beta carotene, in the primary prevention of cancer
incidence and mortality.
Subjects and Methods
Study Design and Population
The Women’s Antioxidant Cardiovascular Study (WACS)
(ClinicalTrials.gov identifier NCT00000541) is a randomized,
double-blind, placebo-controlled, 2 × 2 × 2 factorial trial evaluat-
ing the benefits and risks of synthetic vitamin C (500 mg of ascor-
bic acid daily), natural-source vitamin E (600 IU of ? -tocopherol
every other day), and beta carotene (50 mg of Lurotin every other
day) among women at high risk for cardiovascular disease (CVD).
Vitamin C and beta carotene were supplied by BASF Corp
(Wyandotte, MI) and vitamin E was supplied by (Cognis Corp,
LaGrange, Il). Approximately 2 – 3 years after random assignment
to the antioxidant arms, a folic acid – vitamins B6 and B12 compo-
nent was added to the trial, yielding a four-arm factorial trial. The
WACS trial was approved by the Institutional Review Board of
the Brigham and Women’s Hospital (Boston, MA). The trial’s
independent Data and Safety Monitoring Board met annually to
review the results. Written informed consent was obtained from
The design of the trial has been described in detail ( 41 , 42 ).
Briefl y, between September 1992 and May 1995, 53 788 women
from a pool of more than 450 000 respondents to an invitation
packet of the Women’s Health Study ( 25 , 43 , 44 ) were considered
likely to be eligible for the study and were sent the WACS invita-
tional mailing. Women were considered to be eligible to partici-
pate in the WACS if they were at least 40 years of age; were
postmenopausal or not intending to become pregnant; and had
known CVD or at least three of the following cardiac risk factors:
hypertension, high cholesterol level, diabetes, parental history of
myocardial infarction, or obesity (ie, body mass index ≥ 30 kg/m 2 ).
Women were excluded if they had a self-reported history of cancer
(except nonmelanoma skin cancer) within the past 10 years, had
active liver disease or cirrhosis, had chronic kidney failure, were
current users of anticoagulants, or were unwilling to avoid out-of-
study use of vitamins A, C, and E and beta carotene at intakes
exceeding the recommended daily allowance during the trial.
Between June 1995 and October 1996, a total of 8171 women
were randomly assigned according to a 2 × 2 × 2 factorial design.
Results for the trial’s primary endpoints of major cardiovascular
events have been reported previously ( 42 ). We excluded women
from this analysis who reported having had a diagnosis of cancer
(n = 544) more than 10 years ago because the etiologic factors for
primary and recurrent cancer incidence are likely different ( 45 – 47 ).
As a result, 7627 women (93.3%) free of cancer at enrollment were
included in this analysis for the primary prevention of cancer inci-
dence and mortality ( Figure 1 ). We had more than 90% power,
with a two-sided test ( ? = .05), to detect the individual effect of
vitamins C and E and beta carotene with a 30% reduction in the
risk for total cancer incidence. Power to detect the individual effect
of vitamins C and E and beta carotene with a 40% reduction in the
risk for cancer death was more than 80%.
Study Treatment and Follow-up
After random assignment, participants received a supply of
monthly calendar packs containing antioxidant supplements or
placebo as well as follow-up questionnaires on compliance, poten-
tial adverse effects, occurrence of endpoints, and risk factors that
were sent every 6 months for the first year and annually thereafter.
Study treatment and endpoint ascertainment were continued in a
blinded fashion through January 31, 2005, the scheduled end of
the trial. In July 2006, follow-up and validation of reported end-
points were complete and morbidity and mortality follow-up
were completed for 93% and more than 99% of subjects,
respectively ( 42 ).
Compliance for use of the three antioxidants has been reported
elsewhere ( 42 ). Compliance, defi ned as having taken at least two
CONTEXT AND CAVEATS
Although some observational studies suggest that a diet high in
fruits and vegetables and thus antioxidants may be associated with
a reduced risk of cancer, randomized trials have not supported this
Randomized controlled trial using a factorial design with hazard
ratios from Cox regression models to compare intervention
This study, which was designed to have 80% power to detect a 30%
reduction in the overall risk of cancer, suggests that long-term
dietary supplementation with any combination of the antioxidants
vitamin C, vitamin E, or beta carotene does not reduce the risk of
cancer or the risk of dying from cancer.
There is no basis for a recommendation that individuals increase
dietary levels of antioxidants as a means of reducing cancer risk.
This study had very limited statistical power to investigate any
effect of dietary antioxidants on the risk of specific cancers.
From the Editors
JNCI | Articles 23
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Grant HL46959 from the National Heart, Lung, and Blood Institute and
grants CA112529 and CA126846 from the National Cancer Institute.
The study sponsor had no role in the design of the study; the collection, analysis,
and interpretation of the data; the writing of the manuscript; or the decision to
publish. J. M. Gaziano has received pills and packaging for another study from
We acknowledge the invaluable contributions of the WACS staff, includ-
ing Jean MacFadyen, Eleanor Danielson, Marilyn Chown, Shamikhah Curry,
Margarette Haubourg, Felicia Zangi, Tony Laurinaitis, Geneva McNair,
Philomena Quinn, Harriet Samuelson, Ara Sarkissian, Natalya Gometskaya,
and M. V. Moorthy. We also thank the cancer endpoints reviewers including
Wendy Chen, I-Min Lee, and Shumin Zhang. Finally, we are indebted to the
dedicated WACS participants.
Manuscript received April 23 , 2008 ; revised October 3 , 2008 ; accepted
October 30 , 2008 .