The trial will be carried out in District 1,2,3,7 and 8 of Kabul (latitude 34.280 N), where the vitamin D deficiency prevalence study was conducted in 2005. Most of these are old parts of Kabul with narrow, shaded lanes often with roofed tops between high walled mud houses; most houses have small courtyards with high walls so that for much of the day sunshine does not reach the courtyard. The population is socio-economically deprived with large families (5-10 children).