The World Health Organization calls tobacco the leading cause of preventable death in the world. In December, the WHO launched a campaign against cigarette smoking in Africa, saying a rapidly growing population is creating “larger and more accessible markets” on the continent for tobacco companies.

In part of one of the serious smoking in Africa we examine smoking's effect on health. The act of lighting a cigarette and taking a puff is simple enough, but it triggers complex physical changes within the body. And Dr. Ana Navas-Acien says those changes begin within seconds of inhaling.

“The respiratory airway is very effective in absorbing tobacco and all the tobacco components. Tobacco has thousands of components, including many toxicants and many carcinogens. And so these components go immediately to the blood stream, to the respiratory tract,” she says.

Carcinogens are substances that can lead to the development of cancer, a well-known risk of smoking. But Navas-Acien, professor of preventive medicine at Johns Hopkins University, says cancer can be a long-term consequence of tobacco smoking. There are much quicker unhealthy effects, such as nicotine addiction.

“The most addictive component in tobacco is nicotine. And so nicotine reaches the brain in less than a second. So it’s like a peak of nicotine and that immediate response to nicotine is where the addictive power of tobacco is,” she says.

The brain actually has receptors for nicotine – structures that receive and bind to specific substances.

“So, it’s going to target these receptors that are in the brain cells. And actually the number of receptors is very small in people who do not smoke. But in people who start smoking, the number of receptors for tobacco increases. And the younger people start smoking the higher the number of receptors. That means the more addictive you are going to be,” the doctor says.

Heart, veins, arteries

While the body craves nicotine once addiction sets in, damage is being done to the cardiovascular system.

“The cardiovascular disease effects can be quite short term. There can be changes in the platelets that are very important particles in the blood that form clots. For example if we have a wound then we need these platelets to aggregate so that there is a clot and we don’t bleed. However, if we don’t have a wound and if we smoke then the platelets aggregate – that’s going to potentially contribute to the forming of (a) thrombosis and heart attacks, says Navas-Acien.

A blood clot in the wrong place can stop the flow of blood to the heart, triggering a heart attack.

Cigarette smoke also reduces lung function, even if inhaled as second-hand smoke.

“We have some very good evidence from workers in bars in Scotland. And their lung function was measured when smoking was allowed in the restaurants. And then Scotland passed a smoke-free legislation, so it was not possible to smoke in restaurants any longer and in bars any longer. When their lung function was measured a year later their lung function had improved quite substantially,” she says.

The Johns Hopkins doctor conducted a similar study in Accra, Ghana, measuring the effect of smoking in public places. People who worked in those environments, whether smokers or not, had higher levels of cigarette chemicals in their bodies. Another study was done in Nigeria, but those results are pending.

Looking older

The physical changes taking place inside the body can’t readily be seen without the aid of medical equipment. But there are telltale signs on the outside.

She says, “The skin is going to age more rapidly. For instance, if we take some twins, one who smokes and the other one doesn’t, and they do everything exactly the same, the skin of the person who smokes is going to have more wrinkles and is going to look much older. Maybe like even 10 years older.”

Then there are the yellow teeth and fingernails and discolored gums. Navas-Acien says smoking is also very bad for dental health.

She admits quitting is not easy, whether it’s done by sheer willpower or with the help of medication. It may take numerous attempts to break the nicotine addiction, but the Johns Hopkins professor says it’s worth it.

carcinogen: a substance that can cause cancer 致癌物

cardiovascular: relating to the heart and blood vessels （病等）心血管的；侵袭心血管的

platelet: a very small blood cell, shaped like a disc.Platelets help to clot the blood when a person bleeds 血小板

thrombosis: a serious condition caused by a blood clot(= a thick mass of blood) forming in a blood vessel(= tube) or in the heart 血栓形成

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（来源：VOA 编辑：陈丹妮）