Abstract
Frailty can be quantified in people by counting the accumulation of deficits in health (signs, symptoms, diseases) to construct a “frailty index” (FI). We have quantified frailty in naturally-ageing mice by counting differences in >30 health-related variables (hemodynamics, blood work, activity, body composition). We showed that 30 month-old mice had higher FI scores than 12 month-old animals (0.43 ± 0.03 vs 0.08 ± 0.02; p<0.001; n=12). Similar results were obtained when FI scores were calculated based on clinically-apparent signs of deterioration in mice. Mice treated with known longevity interventions (caloric restriction, resveratrol) had lower FI scores than untreated controls. Importantly, the relationship between FI scores and age (normalized to 90% mortality) was similar in mice and humans; the highest scores were close to the submaximal frailty limit of 0.67 in humans. This ability to quantify frailty in animals will help understand the biology of frailty and provide a platform to test new clinical interventions.