Adolescent Idiopathic Scoliosis (AIS) is a prevalent condition mainly affecting females with disease onset at early puberty. It can lead to serious health problems and is associated with low bone mass which can persist with growth. Osteopenia is found to be an important prognostic factor for curve progression in AIS. Nutritional studies indicated AIS subjects had low dietary calcium intake. Evidences suggested that Vit D insufficiency could be present in AIS. Calcium and vitamin D supplementation can therefore be a viable treatment option for low bone mass in AIS subjects. The primary objective of this prospective randomized double-blinded placebo-controlled trial is to find out whether calcium and vitamin D supplementation can improve bone mineral density (BMD) in osteopenic AIS subjects. The secondary objective of this study is to evaluate whether the supplementation is effective in controlling curve progression in AIS.