The time we fall asleep could matter more for our weight than previously thought.
A study of people at high risk of diabetes identified a surprising association between bedtime and weight loss. The researchers observed this relationship even after taking sleep duration into account.
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The New York University team followed 196 adults aged 21 to 64 for eight weeks. All of them usually slept less than six and a half hours per night. They also had prediabetes: their blood sugar levels were higher than normal but had not reached the diabetes threshold.
The participants followed a program that included advice on diet, physical activity and stress management. Half of them also attended sessions focused on sleep. These sessions included gradually adjusting bedtime and adopting better habits for falling asleep.
To track changes, the participants wore a wrist device to record their rest periods. Another sensor regularly measured the sugar present in their bodies.
The most striking result emerged when all participants were considered together. Each hour earlier than their usual sleep onset time was associated with approximately 0.6 kg of additional weight loss over eight weeks. This relationship persisted regardless of the number of hours spent sleeping.
The researchers now want to better understand whether directly changing sleep onset time can lead to weight loss. To find out, studies will be needed that can distinguish the effect of bedtime from that of other daily habits, particularly diet and physical activity.