Cancer Research 52: 6583-6587 December 1,1992 "Potent Preventive Action of Alpha-Carotene Against Carcinogensis and Promoting Stage of Lung and Skin Carcinogenesis in Mice Are Suppressed More Effectively by Alpha-Carotene Than by Beta-carotene"
Although beta-carotene has been considered to be a key cancer preventive agent in green and yellow vegetables, other types of carotenoids, such as alpha-carotene, may also contribute to anticarcinogenic action, since these carotenoids usually coexist with beta-carotene and are detectable in human blood and tissues. In this study, we compared the inhibitory effect of natural alpha-carotene, obtained from palm oil, with that of beta-carotene on spontaneous liver carcinogensis in C3H/He male mice. The mean number of hepatomas per mouse was significantly decreased by alpha-carotene supplementation (per os administration in drinking water at a concentration of 0.05%, ad libitum) as compared with that in the control group (P<0.001, Student's t test). On the other hand, beta-carotene, at the same dose as alpha-carotene, did not show any such significant difference from the control group. Furthermore, we also compared the antitumor-promoting activity of alpha-carotene with that of beta-carotene against two-stage mouse lung carcinogenesis (initiator, 4-nitroquinoline l-oxide; promotor, glycerol). Alpha-carotene, but not beta-carotene, reduced the number of lung tumors per mouse to about 30% of that in the control group (P<0.001, Student's t test). The higher potency of the anti-tumor-promoting action of alpha-carotene compared to beta-carotene was confirmed in other experimental system; e.g., alpha-carotene was also found to have a stronger effect than beta-carotene in suppressing the promoting activity of 12-O-tetradecanoylphorbol-13-acetate on skin carcinogenesis in 7,12-dimethylbenz(a)anthracene-initiated mice. These results suggest that not only beta-carotene, but also other types of carotenoids, such as alpha-carotene, may play an important role in cancer prevention.
Additional data from table 3:
Group Mean number of tumors/mouse Control 6.31 0.005% alpha-carotene 5.07 0.05% alpha-carotene 3.00 0.005% beta-carotene 7.38 0.05% beta-carotene 4.71 0.005% palm-oil carotenes 3.60 0.05% palm-oil carotenes 2.06
Note: Palm-oil carotenes consist of 30% alpha-carotene, 60% beta-carotene and 10% other (gamma-carotene, lycopene, etc). The best dietary sources for alpha-carotene are (cooked) pumpkin, followed by carrots.