Babies born prematurely have an advanced sleep-wake rhythm in adulthood
Several studies have reported associations between being born prematurely and a tendency towards a morning chronotype. A recent study in the journal Sleep Medicine set out to address this question in a systematic manner. Researchers from Finland recruited 40 adults from the Helsinki Very Low Birth Weight cohort and compared them with 35 healthy control participants, born at term. Participants were matched on age (mean age approximately 25 years) and gender.
All participants were asked to wear an actigraph watch for three days/nights to assess sleep-wake patterning. After adjusting for several clinical and demographic variables it was found that adults born pre-term woke-up approximately 40 minutes earlier than adults who were born at term. The group difference was most pronounced on weekends, where endogenous sleep timing is likely to prevail in the absence of work-time demands. Individuals who were born pre-term also tended to initiate sleep slightly earlier, however this was not statistically reliable. There were no group differences in markers of objective sleep continuity or duration.
The authors note that mechanisms underlying this earlier rise-time and tendency towards an advanced sleep-wake rhythm are not yet clear, but that differences in the pre and post birth environment – deprivation of maternal melatonin, light exposure in neonatal intensive care units – may contribute to early “programming” of sleep-wake timing. Other explanations, such as chronotype preference and prematurity sharing a common genetic origin, cannot be excluded. The study is particularly interesting given the well-documented associations between morningness and optimal/beneficial health outcomes. Findings also indicate the importance of early-life environmental influences on sleep-wake patterning.
Bjorkvist, J. et al. (2014). Advanced sleep-wake rhythm in adults born prematurely: confirmation by actigraphy-based assessement in the Helsinki Study of Very Low Birth Weight Adults. Sleep Medicine, published online 2nd June.