Additional file
Additional file 1:   Questionnaire in English. Abbreviations
CI Confidence interval
HIT-6 Headache Impact Test-6
ICHD-2 The second edition of International Classification of Headache Disorders
IRLSSG International Restless Legs Syndrome Study Group
OR Odds ratio
PSQI Pittsburgh Sleep Quality Index
RLS Restless legs syndrome
VAS Visual analogue scale
Competing interests
The authors declare that they have no conflict of interests.
Authors' contributions
MKC conceived and designed the study, collected and analysed data, and wrote the manuscript. YKJ designed the study and analysed data. JMK conceived the study and collected the data. SJC conceived and designed the study, and wrote the manuscript. All authors read and approved the final manuscript.

Acknowledgements
The authors would like to thank Gallup Korea for providing technical support for the Korean Headache-Sleep study.

Funding
This study was supported by a 2011 grant from the Korean Academy of Medical Sciences.