I googled it.
"...conventional medical wisdom, which states that smokers, former smokers and asbestos workers shouldn't take beta-carotene supplements. Despite convincing scientific evidence that people who eat a lot of fruits and vegetables containing beta-carotene are less likely to develop cancer and heart disease, the results from two well-designed clinical trials yielded surprising results. One, conducted in Finland by the U.S. National Cancer Institute (NCI) and the National Public Health Institute of Finland, found 18 percent more lung cancers and eight percent more overall deaths among 29,133 male smokers given a supplement containing 20 mg of beta carotene and 50 mg of vitamin E. A second study, also funded by NCI testing the effects of beta carotene supplements found 28 percent more lung cancers and 17-percent more deaths among participants taking supplements of beta-carotene and vitamin E. This study included 14,254 men and women between the ages of 50 and 69 who were smokers or former smokers as well as 4,060 men between 45 and 69 who had been exposed to asbestos at work." (
link - Should Smokers Avoid Beta-Carotene?)