BioEd Online

Smoking is doubling the number of people dying from tuberculosis (TB) in India, a new study warns¹. A similar cloud may be hanging over other developing countries.

About half of the 400,000 men who die from TB in India each year do so because of smoking, the investigation found. Smoking appears to quadruple the risk of falling ill with the disease, by helping dormant TB bacteria blossom into a full-blown lung infection.

The result is the first convincing link between smoking and TB. It also contrasts with the plight of smokers in the Western world, who are more likely to die from lung cancer and heart disease. Smokers in India also have higher rates of these diseases. "It's a surprise," says study member Prabhat Jha of the University of Toronto, Canada.

Researchers fear that tobacco may also exacerbate the impact of TB in Africa, China and in other countries where the disease is rife. Women in India and China, who rarely smoke now, might also become increasingly vulnerable as more take up the habit.

"We're looking in the future at a real epidemic," says Tom Glynn, director of cancer science and trends at the American Cancer Society. Around one billion people catch tuberculosis each year, and roughly 1.6 million die. It can be treated with drugs, but these are not widely available in many developing countries.

Even in North America and Europe, smoking might intensify TB's impact. Although rare, the disease has returned to some places recently, as have new drug-resistant strains. "It's a concern," says Glynn.

Smoke screen

Previous epidemiology hinted that smoking might increase the risk of TB. But the threat has been neglected because most studies were in the West, where the disease is uncommon. "It just got forgotten," says team member and epidemiologist Richard Peto of the University of Oxford, UK.

The group examined 43,000 men who had died in the late 1990s and a further 35,000 still living in the southern Indian state of Tamil Nadu. TB was far more likely to have killed smokers, they found.

Jha reckons that smoking increases people's vulnerability to whichever disease is already widespread in a population, be it TB, cancer or heart disease. But researchers are not sure whether quitting smoking lowers the risks from TB as it does from cancer.