What is the potential importance of taking beta-carotene?

Beta-carotene is a precursor to vitamin A, but may have a separate role in human health. Controlled research has shown that beta-carotene supplements can increase the numbers of some white blood cells and enhance cancer-fighting immune functions in healthy people who take 25,000 to 100,000 IU per day. However, some studies of smokers have reported that supplements of synthetic beta-carotene increased the risk of both heart disease and lung cancer. Other trials found no positive or negative effect of synthetic beta-carotene on the risk of many other diseases, including several types of cancer,angina pectoris, diabetes, age-related eye disease, or intermittent claudication. Natural beta-carotene, though similar to synthetic, was found in one preliminary study to reverse pre-cancerous changes, while synthetic beta-carotene did not.No other studies have investigated whether natural beta-carotene could be more effective than synthetic in preventing other diseases, but the potential harm from taking synthetic beta-carotene suggests it should be avoided by smokers.