Carotenes in Cancer Prevention
Population-based epidemiological studies clearly demonstrate a strong inverse correlation between dietary carotene intake and a variety of cancers involving epithelial tissues (lung, skin, uterus, cervix, gastrointestinal tract, etcetera). The epidemiological association is much stronger for carotene than for vitamin A. This may reflect carotene’s superior antioxidant, immune-potentiating activity and anticarcinogenic activity.
: No one would argue that a diet high in carotenes is not protective against cancer (except, perhaps, Victor Herbert, M.D., a longtime crusader against nutritional supplementation). The big question is, can beta-carotene supplementation reduce the risk of cancer? The answer appears to be no, that on its own beta-carotene supplementation does not reduce the risk of cancer. Three highly publicized reports on cancer prevention trials featuring synthetic all-trans beta-carotene in high-risk groups have produced negative results. However, before we close this issue, let’s take a closer look at each of these studies to help put things into perspective.
Alpha-tocopherol, Beta-carotene Cancer Prevention Study Group
Here researchers studied 29,000 men in Finland who smoked and drank alcohol.The men took beta-carotene (20 milligrams daily) and/or vitamin E. The results of this study indicated an 18 percent increase in lung cancer in the beta-carotene group. This result was not unexpected. Studies in primates have demonstrated that when animals ingest alcohol and beta-carotene, they experience an increase in liver damage as a result of oxidative damage. Other researchers have pointed out that beta- carotene is very susceptible to oxidative damage. To protect against oxidative damage of beta-carotene, other antioxidant nutrients need to be present. Absence of these protective nutrients could result in the formation of cancer-causing compounds, which further stresses the importance of relying on foods and broader-spectrum nutritional antioxidant support. For example, the group that received both beta- carotene and vitamin E did not show an increase in cancer. In addition, the group that did not receive beta-carotene supplements demonstrated a strong protective effect of high dietary beta-carotene and blood carotene levels against lung cancer. All together this data strongly suggests that the protection offered by beta-carotene is apparent only when other important antioxidant nutrients are present.