Smokeless tobacco and coronary heart disease: risks among non-smokers in Bangladesh.

Background Most epidemiological studies exploring the association between smokeless tobacco (SLT) use and coronary heart disease (CHD) have been in Western populations and have focused on the SLT products used in those countries. Studies from South Asia are limited and the results have been inconsistent. There is widespread use of SLT products in Bangladesh particularly associated with betel chewing, with a prevalence of 27% among the Bangladeshi adult population including urban and rural. Objectives ￭ To determine whether there is an association between SLT use and CHD among non-smoking adults in Bangladesh. ￭ To explore the perceptions of Bangladeshi adults regarding health effects of SLT use. ￭ To assess whether hospital controls can be used in case-control studies with minimal bias, where resource constraints limit recruitment of community controls. ￭ To determine the utility of the Rose Angina Questionnaire (RAQ) for detecting CHD among Bangladeshi adults. Methods A case-control study of non-smoking adults aged 40-75 years, residing within Dhaka City Corporation areas, was conducted in 2010. Cases of CHD were selected from two cardiac hospitals. Controls were selected from both hospital and community settings. Cases were classified as incident cases (diagnosed within last one-year) of CHD if diagnosed as such by the hospital cardiologists. Neighbourhood residents of the CHD cases, not known to have any cardiac disease, were selected as community controls. Hospital controls were those patients who attended cardiac outpatient departments, but on clinical examination were considered not to have CHD by attending cardiologists. Four community controls were matched to each case on age (±5 years), gender, residential area and socioeconomic status. One hospital control was matched to each case on age and gender. A structured questionnaire was used for the case-control study and a semi-structured questionnaire was used to explore perceptions of SLT use. The RAQ was also used to re-classify cases and controls, and to validate its utility in Bangladesh. Results The study enrolled 302 cases, 1208 community controls, and 302 hospital controls (male: female 50:50; mean age 53±8.5years). Current (during the last one year) use of SLT was higher among community controls (38%) compared to cases (33%) and hospital controls (32%). Current use of SLT was not associated with an increased risk of CHD when community controls were used (adjusted OR 0.87, 95% CI 0.63-1.19, p>0.05), when hospital controls were used (adjusted OR 1.00, 95% CI 0.63-1.60, p>0.05), or when both controls were combined (adjusted OR 1.00, 95% CI 0.74-1.34, p>0.05). All analyses were adjusted for potential confounders. Risk of CHD did not increase with use of individual types except gul, frequency, duration, past use of SLT products, or using the RAQ re-classification of cases and controls. There was a significant association between gul use and CHD when both controls were combined (adjusted OR 2.93, 95% CI 1.28-6.70). Study participants believed that Bangladeshi people used SLT products primarily due to addiction (52%) and habituation to SLT products (23%). The influence of family members was the main reason given for initiating SLT use. Almost all respondents (97%) considered SLT products to be harmful, and cited heart disease, cancer and tuberculosis as the major SLT-related diseases. There were significant differences found between hospital controls and community controls in terms of confounding variables, but not for SLT use. The RAQ had a sensitivity of 53%, specificity of 89% and a positive likelihood ratio of 4.8 in detecting CHD among Bangladeshi adults compared with diagnoses done by cardiologists. Conclusions In this study, there was no statistically significant association between SLT use in general and CHD. Public health campaigns should focus on other detrimental health effects of SLT use. Tobacco control activities should consider addressing the role of the family in SLT initiation and use. The study also suggests that in resource constrained settings, carefully selected hospital controls may be an alternative to community controls if confounders are measured and are adjusted for. Finally, the RAQ may be a useful tool in large scale epidemiological research in Bangladesh.Thesis (Ph.D.) -- University of Adelaide, School of Population Health and Clinical Practice, 201