Some people have a natural preference for sleeping late or early and are commonly known as owls and larks. People also often describe themselves as being a morning or evening person. This natural variation is not just a personal preference but is actually genetically determined, it is part of the normal variation in people’s sleep needs. At the extremes this variation can become a disorder that is very disruptive to life – delayed sleep phase syndrome/disorder, or advanced sleep phase syndrome.
Apart from the disorders of sleep phase, which require specialist treatment, it is useful to notice that whether someone is naturally an owl or a lark will contribute to how well they adapt to different occupational routines, for instance people with an evening preference found it easier to tolerate shift work than morning people . Someone’s natural sleep timing preference will also affect at what times of day they perform at their best, and might affect when it is best for them to plan to do certain activities.
It can be useful to acknowledge that the sleep pattern that is natural for one person, can be quite a challenge for another. Whilst it is often necessary for people to adapt to social norms regarding sleep times, sometimes it is suggested that their routine adapts to match their ideal sleep schedule – there has been some research recently for instance on altering the times of school days to suit adolescents who tend to have a more delayed sleep phase on average  .
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