Fig. 2

Circadian (24-hour) distribution of migraine attack onset peak interval for the included studies (n = 15). One study reported migraine attack onset at any time of the day [32] and thus was not included in the figure. Horizontal black lines indicate the reported time range where most migraine attacks began as reported by the individual studies. Black dot was applied if studies reported a specific peak time. Broken lines were applied for three studies where specific time clocks were unreported [3, 23, 43]. Thus, reporting of early morning hours was estimated to 5 am–8 am [3], morning hours was estimated to 6 am–12 pm [43] and after noon was estimated to 12 pm–12 am [23]. n: total sample size