The world's population is becoming increasingly urbanized are a prominent feature of urbanization in the developing world, and two thirds of the world's megacities are located in developing countries .However, the relationship between the characteristics of megacities and the health of their residents is not always clear. Rapidly increasing populations in megacities have been linked to increased environmental pollution (deteriorating air, water, and soil quality), poor housing, high population density and crowding, and poor services such as water and sanitation. Within megacities, slum dwellers have been cited as a particularly vulnerable group. Although increased environmental pollution can plausibly be linked to adverse human health impacts, especially among slum dwellers, this relationship is confounded by the underlying poverty and lack of education of this group, which could independently lead to poor health and nutritional status.