Heart rate variability in the prediction of mortality (ScienceDirect version)

Researchers combined results from earlier studies on heart-rate variability, meaning the small changes in time between heartbeats. These studies followed adults and compared their heart-rate patterns with later deaths from any cause or specific diseases. People with lower variability generally had a higher risk of dying during follow-up. However, the studies used different methods and could not prove that low variability caused the higher risk.

What this means for you: This does not mean a low reading from a smartwatch predicts when someone will die. Heart-rate variability may be one health clue, but it is not a reason by itself to buy a device or change treatment.