Recent studies have shown that smoking and taking Beta Carotene supplements do not go together. Beta Carotene is an antioxidant, which means that it inactivates free radicals in the body. In the process it oxidizes and can become a kind of pro-oxidant or form oxidized by-products. Normally we don't have to worry about the by-products of Beta Carotene's antioxidant behavior. If you maintain a healthy diet with a variety of antioxidants they will work in combination to protect one another from oxidizing.
It appears that smokers on the other hand do have something to worry about. Two studies ending in the nineties found that people who smoked at least one pack a day or drank higher than average amounts of alcohol and took Beta Carotene or Vitamin A supplements were at a higher risk for developing lung cancer and a higher risk of dying. Each of these trials showed that Beta Carotene wasn't helping many of its smoking participants and was in fact hurting some of them. The first trial called The Alpha-Tocopheral, Beta Carotene Cancer Prevention Trial showed eighteen percent more lung cancer and eight percent more deaths in male smokers who took 20mg of Beta Carotene. The second trial called the Beta Carotene and Retinol Efficacy Trial (CARET) initial results showed that there was twenty eight percent more lung cancer in the group of smokers and former smokers it had taking Beta Carotene and Vitamin A and seventeen percent more deaths. These results were so similar to the Cancer Prevention Trial final results that they told the participants to stop taking the supplements before the trial was scheduled to end.
Why is this so? Well, since it's thought that anti-oxidants protect each other from oxidizing scientists suspect that smokers don't have enough of the other types of antioxidant vitamins in their systems to prevent this from occurring. It has been found that smokers have low levels of Vitamin C in their blood stream-and that's' one of the antioxidants. So the Beta Carotene oxidizes in the body after it uses up its antioxidant properties an in effect becomes a free radical damaging or exacerbating damage done to the cells of smokers lungs which leads to abnormal cell growth and cancer. With low levels of other kinds of antioxidants in their bodies there's nothing to stop it. Scientists believe that the two antioxidants that work together to protect the body from Beta Carotene pro oxidant damage are Vitamins E and C.
If you are a smoker you should by no means try to avoid Beta Carotene or Vitamin A in your diet. These trials seem to show that all anti-oxidants work together to prevent cancer and isolating one or the other for consumption, especially in a non-natural form, simply negates its effects and sometimes causes problems. What you should be doing is focusing on eating a lot of foods with antioxidants in combination. There is no evidence as of current that suggests eating foods with Beta Carotene in them can increase the risk of cancer in smokers.