Acknowledgments This study was supported by the International Collaborative Research Grants Scheme
with joint grants from the Wellcome Trust UK (GR071587MA) and the Australian NHMRC (268055). We
thank the staff at Sukhothai Thammathirat Open University (STOU) who assisted with student contact and
the STOU students who are participating in the cohort study. We also thank Dr Bandit Thinkamrop and his
team from Khon Kaen University for guiding us successfully through the complex data processing.