The health of individuals and populations is influenced by many variables. These include genetics and biology, but perhaps more important than these are the social determinants of health. The social, political and economic circumstances in which people live their lives are critical in determining how long they live and with what burden of ill health. These differences are very marked between countries, for example a 15-year-old boy in Lesotho has about a 10% chance of living until the age of 60, compared with a 15-year-old boy in Sweden who has ...