Circadian Disruption Harms Healthspan but Not Lifespan in Mice

A GeroScience study examined what happens when mice live under constantly shifting light-dark cycles (non-24-hour schedules) throughout their lives—mimicking chronic circadian disruption from shift work or jet lag. Surprisingly, while these C57BL/6J male mice showed clear healthspan impairments, their overall lifespan remained unchanged. The disrupted mice exhibited worse metabolic markers, physical function measures, and other health indicators compared to controls on normal 24-hour cycles, yet lived just as long. This finding challenges the assumption that healthspan and lifespan move in lockstep, and has important implications for human aging. It suggests that circadian disruption may condemn us to spending our later years in poorer health without necessarily shortening life itself—arguably a worse outcome than modest lifespan reduction with maintained vitality. For shift workers and frequent travelers, this underscores that circadian health matters for quality of life even if it doesn't show up in mortality statistics. The results also highlight why longevity interventions must be evaluated on healthspan metrics, not just survival curves.