Cohort Profile: the Chennai prospective study of mortality among 500,000 adults in Tamil Nadu, South India.

A prospective study of half a million adults living in the city of Chennai (formerly Madras) arose out of discussions at the 1994 International Cancer Congress in Delhi about how to assess the effects of tobacco on health in different parts of India. Chennai is the capital of the South Indian state of Tamil Nadu, and it is India’s fourth most populous city. Two large-scale epidemiological studies of tobacco and other factors were established: a case-control study that could provide reasonably reliable results quickly, and a prospective cohort study that could provide more robust results over a longer period. (A parallel prospective study of 100000 adults, not included in this profile, is in progress in the nearby rural area of Villupuram; Figure 1.) The case-control analyses, which involved 43000 adult deaths during 1995–97 and 35000 controls who had been living with a case, indicated that smoking is a cause of, among other things, about half of all tuberculosis (TB) deaths among men. The prospective cohort study, which recruited half a million participants between 1998 and 2001, is described here.