A new study done by Brazilian researchers suggests that people whose internal clocks are set later (meaning their natural preference is to stay up later at night and sleep in later in the mornings) are less emotionally stable than those whose preference is to go to sleep and to wake up earlier.
6436 adults participated in the web based survey and were queried about their sleep patterns, temperament, and energy levels throughout the day. The researchers found that evening people had less emotional control, focus coping skills, and caution than the morning people. The evening people also displayed more affective instability and externalization, and less inhibition than the morning people.
There is certainly a genetic component to whether a person is inclined to be a morning person or an evening person. It is unclear, however, how this relates to the emotional and temperamental characteristics described above. Does this mean that it is the staying up later and getting less sleep which is the cause, similar to what has been demonstrated in other studies looking at the effects of insufficient sleep? Or perhaps that the underlying causes of the reduced emotional control and temperamental instability also affect sleep patterns, in the same way that people with mood disorders often have sleep disturbances?
Dennis Rosen, M.D.
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