In studies involving rodent tumorigenesis, Nishino et al. (1999) demonstrated that zeaxanthin can reduce spontaneous liver tumor formation in C3H/He mice when supplied at the level of 50 ppm in drinking water. Compared to controls (n = 14), of which 36% developed tumors, only 8% of zeaxanthin-treated mice (n = 12) were found to develop tumors. Rodent studies have also shown that lutein reduces the rate for occurrence of lung tumors promoted with 4-nitroquinoline-1-oxide in ddY mice (Nishino et al., 2000). Lutein-treated mice developed an average of 2.2 tumors per mouse compared to 3.1 tumors per mouse for untreated mice. Sprague-Dawley rats treated with the colon cancer initiator, N-methyl-nitrosourea, developed fewer aberrant crypt foci when treated with lutein as compared with control animals (Narisawa et al., 1999).
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