What it is
Frailty is a clinical state in which declines across multiple systems leave a person with little physiological reserve, so that even minor stressors (an infection, a fall, surgery) can trigger an outsized loss of function.
Why it matters for longevity
Frailty strongly predicts hospitalisation, disability and death — often better than age alone. It is closely related to muscle loss, which is why grip strength and gait speed are common screening measures, and it reflects the cumulative burden of the hallmarks of aging.
What the evidence shows
The construct (for example the Fried phenotype) is well-validated for risk prediction. Importantly, frailty is modifiable: resistance exercise, protein-adequate nutrition and managing chronic disease can slow or partly reverse it.
How to act on it
Screen earlier than you think, prioritise strength and protein, and treat reversible contributors — frailty is a target, not a fixed fate.