sleepiness may lead to substance abuse in these individuals. 
Prevalence
The estimated prevalence of advanced sleep phase type is approximately 1% in middle-
age adults. Sleep-wake times and circadian pha se advance in older individuals, probably
accounting for increased prevalence in this population.
Development and Course
Onset is usually in late adulthood. In the familial  form, onset can be earlier. The course is typ-
ically persistent, lasting more than 3 months, but the severity may increase depending on work
and social schedules. The advanced sleep pha se type is more common in older adults. 
Clinical expression may vary across the lif espan depending on social, school, and work
obligations. Individuals who can alter their work schedules to ac commodate the advanced
circadian sleep and wake timing can experience remission of symptoms. Increasing age
tends to advance the sleep phase, however, it is unclear whether the common age-associ-
ated advanced sleep phase type is due solely to a change in circadian timing (as seen in the
familial form) or also to age-related changes in the homeostatic regulation of sleep, result-
ing in earlier awakening. Severi ty, remission, and relapse of symptoms suggest lack of ad-
herence to behavioral and environmental trea tments designed to control sleep and wake
structure and lig ht exposure.