Comorbidities

Recent evidence has shown that tobacco use and exposure to secondhand smoke also interact with other health conditions, making it easier to get sick and harder for other diseases to heal. For instance, smoking exacerbates tuberculosis (TB), it is associated with mental illnesses, and makes HIV patients more susceptible to complications. More recently, there is some evidence that tobacco use makes some smokers more prone to worse outcomes when SARS-CoV-2 infects them such as greater likelihood of hospitalization.

Smoking increases the risk of developing TB and makes its treatment less effective. About 16 percent of deaths by tuberculosis were attributable to tobacco use in 2019 worldwide. However, this proportion can be as high as 28 percent as in the case of Montenegro or Greenland. In China, one quarter of the deaths by tuberculosis were caused by tobacco use.

Tobacco use is more likely to occur among people with any mental illness (AMI), and they also tend to smoke more frequently and with more intensity. For example, a study from the USA found that the prevalence of smoking among adults with AMI in the past year was 33.3 percent, while it was 20.7 percent for those without AMI.

Among individuals with HIV, smoking prevalence is at least twice that in those without HIV infection. Mitochondrial oxidative injury—a key contributor to heart and liver diseases, among others— in smokers may be exacerbated in HIV-infected individuals because several antiretroviral drugs also induce mitochondrial toxicity. Smoking also harms the immune system by promoting inflammation and immune suppression, making HIV patients even more vulnerable to opportunistic infections and complications.

Smoking is also a risk factor for developing diabetes. Moreover, the risk of premature death increases disproportionally when diabetes and smoking occur simultaneously compared to having one of these two conditions alone. Besides deaths, diabetes may cause substantial disability. Worldwide, around 17 percent of the Disability-Adjusted Life Years (DALYs) caused by diabetes are attributable to tobacco use (20 and 13 percent for males and females, respectively). The more significant proportion of DALYs attributable to smoking occur in upper-middle income countries.

Tobacco use makes people more vulnerable to the adverse effects of COVID-19 by weakening lung function and immune response, compromising the body’s defense mechanisms against infections. According to recent evidence, tobacco use is an important risk for having severe progression of COVID-19, including increased mortality. The effects seem to be higher among young people.

Interventions aimed to stop smoking initiation and support smokers to quit could help reduce the global burden of disease not only by addressing diseases highly attributable to tobacco, but also by the many other diseases with these pronounced comorbidities. Therefore, smokers would face less healthcare-related costs and could increase their economic productivity because they would be healthier, which is beneficial for all, but especially for the poor because it lightens the burden of tobacco on them.