Epidemiological research has long since observed that the prevalence of hypertension varies across populations' socioeconomic strata. Higher socioeconomic status (SES) has been consistently associated with lower levels of blood pressure in most studies from Europe and North America, while research in low- and middle-income countries at an earlier stage of the epidemiological transition revealed mixed patterns. The causal mechanisms underlying these varying relationships are largely unknown. Only in recent years the pathways through which SES impacts the cardiovascular system have been explored in large-scale studies, with results suggesting that body mass index, heart rate, and to a lesser extent physical exercise, alcohol use and smoking, may play a role in mediating these associations. However, these results refer to high-income countries, while similar research in low- and middle-income countries, and sub-Saharan Africa in particular, is lacking. In 2008, the National Income Dynamics Study (NIDS) collected a broad range of information on a representative sample of the population of South Africa, a medium-income country undergoing rapid epidemiological transition. Among other topics, information was gathered on blood pressure, biologic and behavioural risk factors, education, income and other indicators of socioeconomic position.