Vitamin A and lung cancer.

In a dozen case-control and cohort studies, high intake of fruits and vegetables containing carotenoids has been associated with a reduced risk of lung cancer. In contrast, little relation has been found between intake of preformed vitamin A and this disease. Although initial studies suggested that persons with lower levels of serum retinol have higher future rates of lung cancer, this idea was not confirmed in subsequent investigations. Prediagnostic levels of beta-carotene in blood, however, have been inversely related with risk of lung cancer. Available data thus strongly support the hypothesis that dietary carotenoids reduce the risk of lung cancer, but the data are also compatible with the possibility that some other factor in these foods is responsible for the lower risk. Even if ultimately shown to be casual, the relation between diet and lung cancer is modest compared with the deleterious effect of cigarette smoking.