Additional informed consent will be obtained for collecting blood samples. The sub-samples of children for measuring vitamin D level will be selected by the independent statistician. Venous blood samples will be taken at home by an experienced paediatric phlebotomist, and transported to the trial laboratory at the end of each morning and afternoon in clotted sampling bottles inside vaccine cool-boxes containing ice-packs. They will be centrifuged by experienced and retrained technicians and the extracted plasma frozen and stored at <20◦◦C At the end of the trial all frozen samples will be transported to the AKU Micronutrient Research Laboratory in Karachi for high 4 pressure liquid chromatography (HPLC) to establish vitamin D status.