Blood BDNF level measurement and Genotyping of BDNF Blood will be taken by a trained research staff/research nurse and analyzed at Neuroscience Laboratory, located at the Translational Medicine Centre, Yong Loo Lin School using in-house and commercial assays. 10-20 ml of blood will be taken each time via venipuncture for three times, at before intervention, after and 4 weeks after intervention, respectively, that is, at the same time point of other outcome measurement. In total, 30-60 ml of blood will be collected for each subject for the whole research study. 10ml of blood will be taken from 5 healthy subjects as controls which is needed by the BDNF analysis protocol. To minimize the laboratory error during the test procedure, each blood sample will be processed first to extract plasma and plasma will be stored at -80°C at Tissue Repository, NUH, until all blood samples are collected. All plasma samples will be analysed together after the last collection of blood from the last subject. Any blood specimens obtained during the study will be stored and analyzed only for the purposes of this study for a period not exceeding 5 years and will be destroyed after completion of the study.