There is more news about the deadly effects of smoking. An article in the current issue of The Lancet reports that smoking increases the risk of dying of tuberculosis.
Cigarette smoking and tuberculosis are a lethal combination. After studying 45,000 male smokers in India, in the late 1990's, researchers found that 4,000 died of tuberculosis, or other related lung diseases. That's double the number of non-smokers in a similar-sized group who died of TB during the same period.
Those who smoked "bidi," a small cigarette popular throughout Asia, were also found to have double the risk of fatal TB compared with non-smokers.
Study co-author Prabhat Jha, of the University of Toronto's Center for Global Health Research in Canada, says cigarettes appear to undermine the ability of smokers' immune systems to keep early stages of tuberculosis under control.
"By smoking, it converts sub-clinical disease, in other words, disease that they don't know about, to disease that's more clinical," he said. "That is, they have more symptoms, and eventually, if they are not treated and cured, they can die from it."
According to the World Health Organization, India has the greatest share of the world's approximately 575 million TB infections. The disease kills about two million people each year.
Professor Jha says smokers are spreading tuberculosis, because active disease is highly infectious. People with active TB can transmit the disease to an average of 10 to 15 others. The result is a four-fold increase in the number of people infected with the disease because of their association with smokers.
"So, [that's] the main way it appears to be killing people from TB is increasing the presence of clinical tuberculosis in the first place, not necessarily selectively [only] killing those who already have TB," said Prabhat Jha.
In June, the World Health Organization adopted a tobacco control treaty, signed by most of the organization's 192 members. The treaty calls for advertising bans, larger warning labels on tobacco products and measures to protect non-smokers from second-hand smoke.