Multimorbidity

Multimorbidity is defined as the co-occurrence of two or more chronic conditions within the same person, without designating a primary or index disease — a distinction from the related but person-centred concept of comorbidity. Its prevalence rises sharply with age: roughly 50% of adults over 65 in high-income countries live with three or more chronic conditions. Multimorbidity is strongly associated with polypharmacy, functional decline, reduced quality of life, greater healthcare utilisation and higher mortality, and it challenges single-disease clinical guidelines that were developed in trial populations that often excluded it. In geroscience, multimorbidity is both a key outcome of biological aging and a prime motivation for targeting upstream aging processes rather than individual diseases sequentially.