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1.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
2.Dietary reference intakes for vitamin C, vitamin E, selenium, and carotenoids : a report of the Panel on Dietary Antioxidants and Related Compounds, Subcommittees on Upper Reference Levels of Nutrients and Interpretation and Uses of Dietary Reference Intakes, and the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine. Institute of Medicine (US) Panel on Dietary Antioxidants and Related Compounds. Washington, D.C. : National Academy Press, c2000. http://www.ncbi.nlm.nih.gov/nlmcatalog/100938980