Importance of  -Carotene, beta-Carotene, and Other Phytochemicals in the Etiology of Lung Cancer

Of all proposed cancer chemopreven-tive agents, p-carotene seemed the mostpromising (7)—until recently. Numer-ous retrospective and prospective studieshave demonstrated that a reduced risk oflung and other cancers is associatedwith an increased intake of provitaminA carotenoids, the vitamin A precursorsin vegetables and fruits (2-7). Inprospective studies, elevated prediag-nostic blood P-carotene levels havebeen consistently predictive of a re-duced incidence of lung and other can-cers (2-5,7,8). However, in a large,randomized, placebo-controlled trial inFinland (9), male smokers took P-carotene daily for 5-8 years at a dosesubstantially higher than that linked toreduced risk in observational studies,and lung cancer incidence was increased18% (95% confidence interval CI -3%-36%), contributing substantially toan 8% excess in total mortality. Interimresults from a second large, randomizedtrial conducted in the United States withmale and female smokers and men ex-posed to asbestos have corroborated thatlung cancer incidence and total mor-tality are increased in subjects taking P-carotene supplements.'The observational studies of diet andcancer relied on food composition tablesto estimate consumption of total pro-vitamin A carotenoids, which include p-carotene, a-carotene, and chemicallysimilar carotenoids. Recently, adatabase detailing the levels of themajor individual carotenoids in U.S.foods was published (10,11). Conse-quently, we reanalyzed data from thefirst case-control study to evaluate thehypothesis that P-carotene could protectagainst cancer—a population-basedstudy of diet and lung cancer conductedin New Jersey during 1980-1981(12,13).Eligible case subjects were whitemen