😴 Researchers analyzed six objective traits—bedtime, wake‑time, 24‑h rhythm strength, day‑to‑day stability, sleep efficiency, and fragmentation—using machine‑learning on 600 million wrist‑movement data points. Poor scores on any trait pushed the combined disease burden higher across metabolic, cardiovascular, digestive, and mental categories, explaining up to one‑fifth of future illness. Actigraphy, long a gold‑standard chronobiology tool, lets scientists sidestep memory bias that plagues questionnaire studies.⁠ ⁠ Misclassified “long sleepers” illustrated the danger of eyeballing sleep: 21.7 % who said they snoozed ≥9 h slept <6 h, inflating old links between long rest and stroke. Regularising bedtime could therefore become a low‑cost lever in national prevention plans—on par with diet and exercise guidance. The team is now validating the risk scores in U.S. datasets and testing whether app‑based coaching or blue‑light curfews can nudge circadian steadiness and, in turn, trim multimor...