Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. - Omenn,G.S.; Goodman,G.E.; Thornquist,M.D.; Balmes,J.; Cullen,M.R.; Glass,A.; Keogh,J.P.; Meyskens,F.L.; Valanis,B.; Williams,J.H.; Barnhart,S.; Hammar,S. (N Engl J Med, 1996)