In the middle of the 1990s beta-carotene became the subject of controversy when two studies reported that the intake of very large amounts (10 to 15 times the recommended daily dose) of the carotenoid over many years as supplements had led to an elevated risk of lung cancer and mortality in heavy smokers (see Beta-Carotene/Safety). Scientists who had hoped they had found a “miracle cure” for the harmful effects of smoking were disappointed. It became clear that taking high doses of micronutrients cannot compensate for an unhealthy lifestyle or smoking – the real risk factor for the development of lung cancer.
Although no harmful effects of high doses of beta-carotene were found in studies with non-smokers, and even in other studies with smokers no such effects were observed, it was decided to limit the recommended intake of beta-carotene via dietary supplements and fortified foods to 20 mg beta-carotene per day for smokers.
From this point on, beta-carotene had a bad reputation. This completely ignored the fact that, as a vitamin A precursor (‘provitamin A’), it represents a safe and for many possibly the most important source of vitamin A. Among other things vitamin A is important for maintaining the mucous membranes and in the immune defense against infectious diseases. Since the consumption of vitamin A rich foods, in particular liver, is often not sufficient to meet requirements, beta-carotene has a key role to play here.