23.Greenberg ER, Baron JA, Karagas MR, Stukel TA, Nierenberg DW, Stevens MM, Mandel JS, Haile RW.Mortality associated with low plasma concentration of beta carotene and the effect of oral supplementation. JAMA. 1996 Mar 6;275(9):699-703. http://www.ncbi.nlm.nih.gov/pubmed/8594267
24.Goodman GE, et al. The Beta-Carotene and Retinol Efficacy Trial: incidence of lung cancer and cardiovascular disease mortality during 6-year follow-up after stopping beta-carotene and retinol supplements. J Natl Cancer Inst. 2004;96(23):1743-50. http://www.ncbi.nlm.nih.gov/pubmed/15572756
25.Martini MC, Campbell DR, Gross MD, Grandits GA, Potter JD, Slavin JL. Plasma carotenoids as biomarkers of vegetable intake: the University of Minnesota Cancer Prevention Research Unit Feeding Studies. Cancer Epidemiol Biomarkers Prev. 1995 Jul-Aug;4(5):491-6. http://www.ncbi.nlm.nih.gov/pubmed/754980410