Overview
- A pooled randomized analysis published July 6 in Annals of Internal Medicine assigned 95 adults who usually slept 7–8 hours to two six-week phases and found that delaying bedtime by about 90 minutes produced an average weight gain of roughly 1 pound and increased sedentary time.
- Activity trackers showed overall sedentary time rose by about 17 minutes per day during the short-sleep phase and by nearly 30 minutes per day for men and postmenopausal women, which researchers link to greater tiredness and lower daily movement.
- Study protocols measured weight, waist circumference, body composition and fasting hormones and the authors point to hormonal changes, more hours awake to eat, and reduced activity as plausible mechanisms for the weight gain.
- Related analyses of the same participants reported increased insulin resistance in women with cardiometabolic risk and signs of cardiac inflammation in higher-risk participants, raising concerns about downstream effects beyond modest short-term weight change.
- The trial was designed to mimic chronic mild sleep deprivation that about a third of adults report, but its six-week phases and 95-person pooled sample limit conclusions about long-term trajectories and population generalizability, so researchers call for intervention trials to test whether improving sleep prevents or reverses these effects.