Prevalence
About 0.15% of adults, three in 2,000, have DSPD. Using the strict ICSD diagnostic criteria, a random study in 1993 of 7700 adults (aged 18–67) in Norway estimated the prevalence of DSPD at 0.17%. A similar study of 1525 adults (aged 15–59) in Japan estimated its prevalence at 0.13%.
DSPD is not uncommon among teenagers; at least one study has indicated that the prevalence of DSPD among adolescents is as high as 7%. Among adolescents, boys predominate, while the gender distribution shows equal numbers of women and men in adults.
A marked delay of sleep patterns is a normal feature of the development of adolescent humans. According to Mary Carskadon, both circadian phase and homeostasis (the accumulation of sleep pressure during the wake period) contribute to a DSPD-like condition in post-pubertal as compared to pre-pubertal adolescents. Adolescent sleep phase delay "is present both across cultures and across mammalian species" and "it seems to be related to pubertal stage rather than age."
Read more about this topic: Delayed Sleep Phase Disorder
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