Antioxidants and Cancer Prevention
What are antioxidants?
Antioxidants are substances that may protect cells from the damage caused by
unstable molecules known as free radicals. Free radical damage may lead to
cancer. Antioxidants interact with and stabilize free radicals and may prevent
some of the damage free radicals otherwise might cause. Examples of antioxidants
include beta-carotene, lycopene, vitamins C, E, and A, and other substances.
Can antioxidants prevent cancer?
Considerable laboratory evidence from chemical, cell culture, and animal
studies indicates that antioxidants may slow or possibly prevent the development
of cancer. However, information from recent clinical trials is less clear. In
recent years, large-scale, randomized clinical trials reached inconsistent
What was shown in previously published large-scale clinical trials?
Five large-scale clinical trials published in the 1990s reached differing
conclusions about the effect of antioxidants on cancer. The studies examined the
effect of beta-carotene and other antioxidants on cancer in different patient
groups. However, beta-carotene appeared to have different effects depending upon
the patient population. The conclusions of each study are summarized below.
- The first large randomized trial on antioxidants and
cancer risk was the Chinese Cancer Prevention Study, published in 1993. This
trial investigated the effect of a combination of beta-carotene, vitamin E,
and selenium on cancer in healthy Chinese men and women at high risk for
gastric cancer. The study showed a combination of beta-carotene, vitamin E,
and selenium significantly reduced incidence of both gastric cancer and cancer
- A 1994 cancer prevention study entitled the
Alpha-Tocopherol (vitmain E)/Beta-Carotene Cancer Prevention Study (ATBC)
demonstrated that lung cancer rates of Finnish male smokers increased
significantly with beta-carotene and were not affected by vitamin E. (2)
- Another 1994 study, the Beta-Carotene and Retinol (vitamin A) Efficacy
Trial (CARET), also demonstrated a possible increase in lung cancer associated
with antioxidants. (3)
- The 1996 Physicians' Health Study I (PHS) found no
change in cancer rates associated with beta-carotene and aspirin taken by U.S.
male physicians. (4)
- The 1999 Women's Health Study (WHS) tested effects of vitamin E and
beta-carotene in the prevention of cancer and cardiovascular disease among
women age 45 years or older. Among apparently healthy women, there was no
benefit or harm from beta-carotene supplementation. Investigation of the
effect of vitamin E is ongoing. (5)