Aging is characterized by the accumulation of macromolecular damage, which leads to the accumulation of functional deficits. People are living longer lives, but persons with the same chronological age display considerable heterogeneity in their accumulation of deficits. Frailty index (FI) operationalizes frailty as the proportion of health deficits present in each individual, providing vital insights into the aging process and its consequences in terms of mortality risk and healthy life expectancy. In older adults, low selenium (Se) status has been associated with frailty and decreased muscle strength (Beck et al. 2007, Lauretani et al. 2007), but, to date, no studies have examined whether Se status significantly influences the lethality of frailty. The objective of this research was to advance our understanding of the importance of Se for frailty and the aging process and to minimize adverse health consequences associated with increased life expectancy by using a novel animal model of highly successful human aging.