People who stay up later than intended may have a weaker physiological capacity for self-control. A new study published in the Journal of Health Psychology links lower heart rate variability to greater bedtime procrastination. Many individuals experience the temptation to prolong their use of digital devices, or complete further tasks, despite being aware that they should already be asleep—a behavior known as bedtime procrastination. Scientists have previously connected bedtime procrastination to difficulties with managing behavior and emotions. Individuals who struggle to prioritize long-term wellbeing over short-term enjoyment, or who have trouble regulating negative feelings, are thought to be more prone to pushing their bedtime later. What has been less well understood is whether this tendency also has a measurable biological marker. A promising candidate is heart rate variability (HRV), defined as the natural variation in the time between heartbeats. Previous research has demonstrated that a higher level of this variability—particularly the component driven by the body’s calming “rest and digest” nervous system (the vagus nerve)—is associated with adaptability to stress and a greater capacity for …