Smaller body size at birth was also associated with poorer sleep.

In addition, children with short sleep duration were more likely to have been born via caesarean section than were children sleeping longer (23.1 percent versus 8.4 percent respectively).

The study was based on data from 289 children born normally between March and November 1998. Sleep duration and sleep efficiency (actual sleep time divided by the time in bed) were measured objectively by actigraphy at eight years for an average of 7.1 days.

These findings were published in SLEEP.