β-Carotene and the role of intervention studies

Vegetables and fruits are associated with a reduced risk of cancers, including especially lung cancer. The possible protective compounds include a wide variety of phytochemicals. However, for historical, technical, and biological reasons, a great deal of attention has focused on a single agent: β-carotene. Recently, in clinical trials, β-carotene has been shown not to be an effective agent and, perhaps, to be harmful. Possible explanations for this are presented, as is the danger of reductionist approaches to the explanation of the complex nutrition-related biology of cancer.