- The effect of lutein and zeaxanthin supplementation on metabolites of these carotenoids in the serum of persons aged 60 or older. Khachik, F., de Moura, F.F., Chew, E.Y., Douglass, L.W., Ferris, F.L., Kim, J., Thompson, D.J. Invest. Ophthalmol. Vis. Sci. (2006)