Free-running circadian period in adolescents and adults.

Abstract

Sleep timing shifts later during adolescence (second decade). This trend reverses at ~20years and continues to shift earlier into adulthood. The current analysis examined the hypothesis that a longer free-running circadian period during late adolescence (14-17years) compared with adulthood (30-45years) accounts for sleep timing differences. Sex and ancestry were also examined because previous reports find that women and those with African-American ancestry have shorter free-running periods. Circadian period was measured using an ultradian dark-light protocol (2hr dark/sleep, 2hr dim room light [~20 lux]/wake) over 3.4days. Dim light melatonin onsets were measured before and after the ultradian protocol, from which the circadian period was derived. In contrast to our hypothesis, we found that free-running circadian period was similar in adolescents and adults. African-American adults had shorter free-running circadian periods compared with adults of other ancestries. This ancestry difference was not seen in the adolescent group. Finally, we observed a non-significant trend for shorter free-running circadian periods in females compared with males. These data suggest that age-related changes in circadian period after late adolescence do not account for sleep timing differences. These data provide further support for ancestry-related differences in period, particularly in adults. Whether the large difference in circadian period between African-American and other ancestries emerges later in development should be explored.