Adolescents whose high schools start after 8.30am may have fewer migraines than their counterparts who have to get to school earlier, a US study suggests.

Researchers examined survey data from 1012 adolescents with migraine. Half of them started school at 8.30am or later, and the other half started earlier in the morning.

In adjusted analysis, after accounting for total hours of sleep, sex, migraine medication, breakfast habits, school year and homework time, teens with a late start had fewer migraine days (mean 5.8) per month than those with earlier starts (mean 7.1).

Lead study author Associate Professor Amy Gelfand of the University of California says while part of the association is likely due to greater total sleep duration, the link remained even after adjusting for total sleep.