Diabetes fuels TB: study

Diabetes makes a person about three times as likely to develop tuberculosis new research shows.

This alarming new finding spells trouble for South Africa with its high burden of both diabetes and tuberculosis. As much as 8 percent of the population is believed to suffer from diabetes, according to Michael Brown from the Centre for Diabetes and Endocrinology.

In addition, South Africa has the fourth greatest incidence rate of tuberculosis in the world and it is the leading cause of natural death in South Africa. These statistics, combined with the country's high HIV/Aids prevalence (which is a known risk factor for developing TB) makes a very large portion of the South African population extremely vulnerable to developing tuberculosis.

Linking TB and diabetes
To clarify the link between TB and diabetes, researchers at the Harvard School of Public Health in Boston examined data on 1.7 million people from 13 studies done in Canada, Mexico, the United States, Britain, Russia, Taiwan, India and South Korea.

Having diabetes raised a person's chances of getting active TB disease regardless of geographic region, the researchers found, with the risk rising roughly three-fold compared to people without diabetes, the researchers wrote in the Public Library of Science journal PLoS Medicine.

"With an estimated 171 million people afflicted with diabetes, a figure which is expected to double by year 2030, it is clear that (diabetes) constitutes a substantial contributor to the current and future burdens of TB globally," epidemiologist Megan Murray, who conducted the research with Harvard colleague Christie Jeon, said.

There is evidence that diabetes predisposes people to TB infection and impairs their ability to respond to infection, Murray said. Tuberculosis is spread from one person to another when someone with active TB disease coughs or sneezes.

The role of diabetes may complicate efforts to drive down rates of TB, which trails only Aids on the list of the leading killers among infectious diseases, the researchers said.

An estimated one-third of the world's population is infected with the bacterium that causes tuberculosis, a disease that typically attacks the lungs.

Risk factors
To better control TB, scientists are eager to better understand what factors may make a person who is infected with TB bacteria but is not sick - known as latent infection - go on to develop active TB disease.

Aids has been helping drive the onslaught of TB, and this research suggests that diabetes also is producing a deadly interaction with TB.

With diabetes, a person's blood-sugar levels are too high, and this can lead to damage to the eyes, kidneys and nerves, as well as heart disease, stroke and limb amputation.

The findings indicated diabetes may be responsible for more than a 10th of the TB cases in India and China, the nations with the most tuberculosis cases. "The contribution of (diabetes) to the burden of TB may be even higher in countries such as India and China where the incidence (of) TB is greater and mean age is lower," Murray added.

TB kills about 1.7 million people a year, according to the World Health Organization. By region, Asia has the most cases of TB while Africa has the highest rates.

The findings indicate global TB control efforts might benefit from giving extra attention to diabetics when dealing with people with latent TB infections, the researchers said.

"Those areas most affected are those in which the burden of (diabetes) is high and TB is still active. Those would include India, areas of Latin America where (diabetes) rates are high, and specific populations such as some Native American populations in the U.S. which experience high (diabetes) and TB incidence," Murray added. - (Will Dunham/Reuters Health)

Read more:
Diabetes Centre
Tuberculosis Centre

July 2008

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