Prospective Study of 500,000 adults in Chennai, 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.
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. The prospective cohort study recruited half a million participants between 1998 and 2001 with the specific aims of examining the associations of tobacco smoking, quid chewing, alcohol drinking, obesity, blood pressure, respiratory function and other factors with overall mortality, and with cause-specific mortality. A particular feature of this study is use of verbal autopsy reports to confirm the cause of all deaths; a method that has been adopted by other epidemiological studies in India. A re-survey of 10 000 survivors was conducted in 2014.
- In the retrospective study:
- Analyses of 43 000 adult deaths and 35 000 controls indicated that smoking is a cause of, among other things, about half of all tuberculosis (TB) deaths among men.1
- At the baseline survey for the prospective cohort study (1998-2001):
- About one-third of the men aged 35–74 were current smokers of tobacco.
- Smoking was extremely rare among women (99.9% reported never having smoked).
- More women than men in every age group (and 10% vs 6% overall) reported quid chewing (either with or without tobacco in the quid); in both sexes, quid chewing was more prevalent at older ages.
- A quarter of men overall (and even more at younger ages) reported being current drinkers of alcohol, but almost all women (99.9%) reported never having been a regular drinker.
- Mean BMI levels for men and older women were much lower than in most Western countries, but the mean for women aged 35–54 (24.0 kg/m2) was similar to that in some European countries
By 1 January 2015, there were 70 000 deaths of which:
- 6% were due to stroke,
- 35% to IHD or other vascular diseases, and
- 1.5% (women) or 5% (men) were due to TB.
Ongoing analyses are examining the joint relevance of smoking and alcohol to cause-specific mortality and the relevance of blood pressure and body-mass index to cause-specific mortality in non-smokers.
The Chennai Prospective Study is funded through core funding to the Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU) from the Medical Research Council, the British Heart Foundation and Cancer Research UK, with additional support for international studies of smoking from the US NIH Fogarty International Center (grant no 5R01TW005993-02).
Data Access and Sharing
The Chennai prospective study on mortality in Tamil Nadu is a collaboration between CTSU and the Epidemiological Research Center, Chennai, Tamil Nadu, India. Specific proposals for future collaboration or specific analyses, addressed to the study's India-based or Oxford-based investigators, are welcomed. Any requests for the sharing of data will be considered according to the principles set out in NDPH’s data sharing policy. An English language version of the questionnaire is available above.