The aim of the present analysis was to investigate the association between use of electronic media and headache in a population-based sample of adolescents. While bivariate trend tests indicated that there might be differential associations between use of electronic media and prevalence of headache, most effects disappeared when the models were adjusted for socio-demographic variables. Only the associations between frequent listening to music and overall prevalent headache remained significant after adjustment, but this association was no longer seen if the influence of other electronic media was also considered. Thus, specific headache-related effects of frequency of calling with mobile phones, working with computers, watching television/videos or playing with game consoles were not found.
An adverse effect of high use of music on headache was also found by Zarowski et al., who reported that listening to music during nighttime may affect sleep habits and may, therefore, be associated with headache in children and adolescents . However, sleeping habits have not been studied in the present investigation and we are, therefore, not able to test this more in detail. Also the effect of frequent listening to music was not significant after adjusting for the other variables. Furthermore, it can not be concluded whether the habit of "listening to music" is the consequence of frequent headaches, e.g. in the sense a self-therapy by relaxation, or the cause, e.g. in the sense of an additional stressor.
The majority of studies investigating associations between use of electronic media and headache focused on computer or mobile phone use. Most of them found adverse associations for frequent use of computers and both migraine and TTH [27–30]; only the study by Smith et al. did not find a statistically significant effect . In a recent review on health complaints due to mobile phone use  results were controversial: While two studies found a statistically significant association between exposure to mobile phones and headache [[22, 23]; see also [5, 24]], two other studies did not [25, 41]. In a double-blind provocation study no evidence was found that radio frequency fields from mobile phones cause headache . With our present investigation, we also cannot confirm that usage of computer/internet or frequent calling with mobile phones could have an impact on headache.
Up to now we cannot exclude whether some of the isolated effects between specific electronic media and different types of headache (see Table 3) might result from multiple testing. This might especially be the case, as no stringent dose-response effects were observed for any electronic media. These inconsistent results can, therefore, not be regarded as 'true' associations. This has to be investigated in future studies.
Strengths and limitations
The population-based data collection procedure and the application of multiple logistic regression models adjusting for relevant socio-demographic confounders are the major strengths of our investigation. Furthermore, we were able to involve the average duration of use of different types of electronic media within one study and could, therefore, create an overall media index and adjust for the various media types simultaneously.
One limitation of our study was the classification of headache, which was only based on self-reports. However, items of the used headache questionnaire in the present study were based on recently published ICHD-II criteria and were established and validated in comparable studies . Furthermore, prevalences of migraine and TTH in the present study correspond quite well with estimates in other recent studies on headache in adolescents in Europe [18, 19] and, especially, in Germany [20, 21].
In addition, data on media use were based on self-reports, not on objective exposure measurements. Differential misclassification of the exposure (i.e. use of electronic media) or the outcome (i.e. headache) might have been an issue, as reported in studies on awareness bias . However, no stringent statistically significant associations between media use and different types of headache were found. Thus, this type of potential information bias does not interfere with our conclusions.
The use of electronic media in the present study population was different in some aspects in comparison to the nationwide KiGGS study : in the MobilEe study girls seem to use computer/internet more frequently, but music media less frequently than in the KiGGs study, and both girls and boys from the present study population seem to watch television/videos less frequently. These differences in the behavior of use of media reflect the finding that there are slightly more participants from families with higher levels of education [7, 33]. To adjust for this variable, sex and SES were considered as confounders in the present study.
A power problem might have evolved when separate stratified analyses for different types of headache were done, simultaneously adjusting for socio-demographic confounding variables. Wide CIs, for example for the subgroup of participants with migraine, arose. However, also analyses comparing any vs. no headache, where no power problem could be observed, revealed no statistically significant effects of mobile phone calls, use of computer/internet, television/videos and game consoles.
With respect to the present objectives, a cross-sectional study might provide limited evidence. Corresponding to many other studies investigating associations between use of electronic media and headache, we conclude that the former might rather be treated as risk factors. However, we cannot exclude the possibility that subjects suffering from headache might have reduced their use of electronic media. Such behavior is not unlikely, since there is an ongoing public debate on adverse effects of use of media on health. To adjust for such effects which might have counterbalanced possible adverse effects of electronic media on headache, a longitudinal study which not only assesses the temporal sequence of electronic media use and onset of headache disorders, but also monitors age effects within groups with similar electronic-media use, might provide a better approach.