According to the Global Adult Tobacco Survey India, 2016-17, close to 267 million adults (15 years and above) in India (29% of all adults) consume tobacco. Unlike most of the developed world, smokeless tobacco (SLT) is the predominant mode in which tobacco is consumed, in products such as khaini, gutkha, betel quid with tobacco and zarda. India also has a significant burden of tuberculosis, with 195 incident patients per 100,000 population.
Is it a coincidence that the country that has the highest number of patients with tuberculosis is also the second highest consumer of tobacco? While common risk factors are low socioeconomic status, malnutrition and educational status, there are clear indicators that tobacco and tuberculosis are causally associated. Those who smoke are twice as likely to get TB, and over thrice as likely to die of the disease. In addition, recent studies suggest that smoking also negatively influences treatment success and risk of relapse. In 2011, we argued strongly in favor of addressing smoking cessation as a key pillar of eradicating TB in an article “Why “STOP TB” is incomplete without “QUIT SMOKING”
What about SLT? While the observed association of smoking with an airborne pathogen seems obvious, several studies have reported a higher prevalence of SLT use among those diagnosed with TB when compared to the general population. There are several postulated mechanisms. Damage to the lining of the mouth, and a chronic inflammatory state caused by SLT impair the body’s defences against TB bacteria. Nicotine and nitrosamines in SLT have been shown, in animal models, to impair cellular immunity (such as macrophage function), increasing susceptibility to infection and disease. What has been observed is that people often use SLT to suppress appetite among impoverished populations, often leading to malnutrition. The link between nutrition and TB has been established, and the malnutrition associated with SLT use could predispose to the disease. There may also be other confounders such as increased susceptibility to oral cancers/pre-cancerous conditions, overcrowding and alcohol use, which are prevalent in SLT users and could predispose to TB. Spitting behaviors associated with SLT also facilitate spread of TB from those with the disease.
Smokeless tobacco cannot be ignored in India’s fight against TB. Firstly, because use of SLT is widely prevalent. This is a public health concern in itself, for multiple reasons such as the development of cancer and cardiovascular disease. Secondly, SLT use may be responsible for the development of TB, through immunosuppressive mechanisms. Thirdly, even if the association isn’t causal, SLT use is associated with TB, and identifying SLT users and helping them quit is an opportunity to screen for asymptomatic (subclinical) TB, identify and offer support for risk factors such as malnutrition, diabetes and alcohol use, and thereby prevent the development of the disease.