Aging--causes and defenses.

Recent studies have shown that chromosomes shorten as cells divide and become senescent. Also, deletions in mitochondrial DNA increase markedly with advancing age, presumably secondary to damage from oxygen radicals. Since host defenses against environmental factors also become attenuated, the molecular damage associated with aging may increasingly perturb normal homeostasis and increase the susceptibility to disease and disability. Such age-associated dysfunctions can be targeted and interrupted.