One in three humans globally carries the tuberculosis bacterium in their bodies. For South Africans, where rates of TB disease are the highest in the world, that figure rises to two in three. Half a million South Africans die of TB every year.
In most cases, TB stays dormant ("latent") for life. But, if your body's defences become weakened, the tuberculosis bacteria can activate, and can make you sick and infectious.
HIV-positive people, for instance, whose immune systems are under attack from the virus that causes AIDS, have a considerably higher risk of developing active TB. Indeed, HIV, especially in South Africa which has high prevalence of both diseases, is now considered a “dual” epidemic with TB.
But there are other conditions that raise risk too. Among the less well-publicised, but common groups at high risk are smokers and people with diabetes.
(Other risks for latent TB becoming active include malnutrition, alcohol abuse, indoor air pollution and environmental tobacco smoke, silicosis, and other causes of immune suppression such as taking steroids.)
How diabetes raises your risk for TB
If you have diabetes, your risk for developing TB is thought to be about two to three times greater than normal. There is also evidence that if your diabetes is poorly controlled, the risk for active TB rises even more. This is because among its many potentially negative effects on the body, diabetes impairs the immune system.
Not only are diabetics more likely to develop active TB disease, but the risk of it recurring, and the risk of it being fatal, are also higher.
TB is often missed in diabetics, and vice versa – diabetes is not suspected or recognised in people with TB. There is thus perhaps a need for bi-directional screening, as with HIV-TB: active TB should be checked for in diabetes patients, and people with active TB should be screened for diabetes.
In people with diabetes, TB often goes undiagnosed because it presents differently to “classic” TB. In diabetics, TB may present as shadows on the lungs, and lower down in the lung; it may look more like pneumonia to doctors.
There is justifiable concern that, as HIV and TB are fuelling each other, so will diabetes and TB. The world is facing an “epidemic” of diabetes: in 2011 there were 336 million people with the condition; this number is projected to rise to 566 million by 2030.
How smoking raises your risk for TB
The multiple health risks associated with smoking, including such diseases as cancer and heart disease, are well known. Less well known is smoking’s link with TB.
But the World Health Organisation (WHO) estimates that over 60% of TB deaths may be attributable to smoking.
Smoking increases the risk you will be infected with TB in the first place, the risk that latent TB infection will become active TB disease, the risk that TB will be more severe, and the risk that it will be fatal. The longer and more heavily you smoke, the higher your TB risk.
If children living with someone who has active TB are also exposed to second-hand or environmental smoke, it is more likely that they too will develop active TB.
Like HIV and diabetes, smoking is also thought to make the body more vulnerable to TB by weakening the immune system. Another reason may be that smoking damages the cilia, tiny hair-like structures in the respiratory tract that normally help to trap foreign particles in mucus and sweep them out of the body.
About one fifth of the world's population smokes, and most smokers live in developing countries with high TB prevalence, like South Africa. It is estimated that smoking could cause 18 million more cases of tuberculosis, and 40 million additional deaths from the disease worldwide over the next 40 years.
- Olivia Rose-Innes, Health24
Ditiu, L. 2012. Global overview of tuberculosis. Presentation at the International Conference on Lung Health, Kuala Lumpur, November 2012.
Harries, A. 2012. Diabetes mellitus and tuberculosis: current status and implications for tuberculosis control. Presentation at the International Conference on Lung Health, Kuala Lumpur, November 2012.