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Houthoofd K, Johnson TE, Vanfleteren JR.Houthoofd K, et al.J Gerontol A Biol Sci Med Sci. 2005 Sep;60(9):1125-31. doi: 10.1093/gerona/60.9.1125.J Gerontol A Biol Sci Med Sci. 2005.PMID: 16183950Review.