Contribution to authorship
IM had the original idea for the study.
GS, ÅF, ET and AJ planned and performed the study and interpreted the results.
All authors contributed to the interpretation of the data and revision of the manuscript, and gave input at all stages of the study
Details of ethical approval: The study was approved by the Regional Ethical Review Board in Linköping nr 2011/499-31 (13-03-12).