In the 1980’s there were two double blind studies testing cancer beta carotene relationships in smokers and others who had risk factors for developing lung cancer. The study was testing the idea that beta carotene supplements would help prevent lung cancer. Both studies were stopped early, and long-term follow up with study participants showed those who had received the beta carotene supplements had a 16% higher chance of developing lung cancer.
Increased Vitamin A
Beta carotene turns into vitamin A, an antioxidant, once it is in the body. Due to the fact that Vitamin A, or retinol, is a great source of antioxidants (and because studies show increased levels of antioxidants reduces your risk of cancer), the theory is that increased vitamin A is positive. However, too much vitamin A reduces the amount of vitamin E in the body. Low levels of vitamin E increase your risk of cancer.
Thought not completely understood, smokers who ingest large amounts of beta carotene are more likely to develop lung cancer. For non-smokers, their risk of developing lung cancer does not increase with increased intake of beta carotene.
Some scientists involved in the original beta carotene studies believe that the increased levels of beta carotene taken by study participants damage the participants’ cells. However, the cells do not appear to recover from the damage even after the study participants discontinued taking the high levels of beta carotene.
One thing that all the scientists involved in the beta carotene studies do agree on is that a diet rich in fruits and vegetables, even those vegetables that contain beta carotene, does lower your overall risk of cancer.