When Christopher Columbus discovered the Americas, he found the natives using tobacco in much the same manner as it is used today. The American Indians believed it to possess 0medicinal properties, which was the main reason for its introduction into Europe. Tobacco was important in Indian ceremonies, such as the smoking of the pipe of peace.The detrimental effects of tobacco smoking have long been recognised.

As early as the 19th century, isolated reports were circulated that cigar and pipe smoking caused cancer of the mouth. It was not until the 20th century (1950 in fact) that firm evidence was established that lung cancer was directly related to cigarette smoking. Lung cancer is now the most common cause of cancer related deaths in the men of most Western countries. Because cigarette smoking became a popular and fairly widespread habit amongst men during World War II and because this disease has a long latency period, the rise in the incidence of lung cancer during the second part of the 20th century was expected. In the late 20th century, in many countries, as many as one-third of all cancer deaths in men, and 10 percent of those in women, are attributed to cigarette smoking. As the current trend of males to give up smoking continues, the male percentage will decline.

However, increasingly more women picked up the habit in the 1950s and '60s; the proportion of women dying from a tobacco-related cancer thus was increasing.In general, the risk of developing a tobacco-related cancer depends on the intensity of the habit as determined by duration (i.e. number of cigarettes smoked per day, tar content of the cigarette, and the depth of inhalation). Cigarette smoking not only is related to the development of lung cancer but also affects the development of cancer of the bladder, oral cavity, and oesophagus.

As noted, the risk of developing one of these cancers increases with the number of cigarettes smoked per day. Studies have also shown that various cancer sites are affected differently by different tobacco products, as well as by different intensities. In general, however, those sites that come into direct contact with tobacco smoke (the lungs, oral cavity, and larynx) are those that are the most adversely affected by exposure to smoke.Passive smoking (i.e.

, a non-smokers inhalation of smoke produced by smokers in an enclosed space) also appears to heighten the risk of developing lung cancer. Several studies have found that, over the long term, the non-smoking spouses of smokers experience a lung cancer risk that is almost double that of spouses of non-smokers. It should be emphasised, however, that smokers continue to have a much higher lung-cancer risk; the lung-cancer mortality risk for a heavy smoker is 20 to 30 times greater than that of a non-smoker.Smoking is also a prime risk factor in cardiovascular system diseases.

Nicotine is known to contract the blood vessels and to release hormones that raise the blood pressure. Both effects could have an adverse effect on the heart. Smokers have distinctly higher levels of carbon monoxide in their blood than non-smokers. Carbon monoxide readily combines with haemoglobin (almost 100 times more readily than oxygen), causing many physiological effects. One is a decrease in the amount of haemoglobin available to carry oxygen and a resulting increase in the affinity for oxygen of the haemoglobin that is available.

This in turn reduces the availability of oxygen to the tissues. It has been shown that even minute amounts of carbon monoxide decrease the exercise ability of patients with known coronary artery disease.Another important piece of epidemiological evidence linking smoking to disease is that as individuals give up smoking, the risk of lung cancer, coronary artery disease, chronic bronchitis, incontinence, emphysema, and other tobacco-related diseases declines. The speed and degree of this decline depends, as would be expected, on the duration and intensity of the smoking habit. Amongst those who have smoked over 20 cigarettes a day for over 20 years, a minimum of three years must elapse after quitting before a decreased risk for cancer is evident; more than 10 years of abstinence is necessary before the degree of risk approaches that for those who have never smoked.

Public reaction to the reports of the health hazards has been to campaign for the reduction of smoking or, among users, to switch to cigarettes with filter-tips and to prefer brands made of milder tobaccos. There has been a drive by tobacco producing countries to grow types with low nicotine and tar contents.After the major medical revelations about smoking during the 1950s and '60s there was an increasing attempt to lessen the influence of tobacco advertising in several countries. Cigarette manufacturers in Canada agreed to end television advertising in 1972 after a bill to effect that end was passed in the Commons. In West Germany television advertising of cigarettes was to be phased out by the end of 1972.

Following a report by Britain's Royal College of Physicians in January 1971 on the number of deaths from cancer, a health campaign was instituted which included warnings on cigarette packages and antismoking commercials. Television cigarette advertising in the United States ceased as of January 1971. An agreement reached in April 1971 with major American tobacco companies required a health warning in other advertisements: the agreement subsequently became law. Another means of discouraging smoking was increased taxation.

In some countries, especially in Europe, the tax on a pack of cigarettes increased dramatically in the late 20th century. In the United States and several other countries, local governments in the 1980s began prohibiting or restricting smoking in public buildings, and these measures were imitated by the private sector with regard to corporate offices and other places of business.Doctors in the mid-1800s first documented lung cancer, or malignant tumours of the lung. In the early 20th century it was considered relatively rare, but by the late 20th century it was the leading cause of cancer-related death amongst men in some 28 developed countries, including the United States. During the 1980s it surpassed breast cancer as the leading cause of death from cancer among women in the United States.

This rapid increase in the incidence of lung cancer was due mostly to the increased use of cigarettes that began after World War I. The world wide incidence in the disease was expected to increase in future decades as a result of the spread in cigarette smoking, particularly among women and in the developing countries.Lung cancer occurs primarily in persons between 45 and 75 years of age. In the late 20th century, in countries with a prolonged history of cigarette smoking, between 80 and 90 percent of all cases of lung cancer were caused by cigarette smoking. Heavy smokers have a greater likelihood of developing the disease than do light smokers.

The risk is also greater for those who started smoking at a young age. Passive inhalation of cigarette smoke is also linked to lung cancer in non-smokers. In the early 1990s it was estimated that passive smoking caused some 2,500-3,300 lung cancer deaths each year in the United States, or about 2 percent of all U.S. lung cancer deaths.

In the earliest stages of lung cancer there are often no symptoms. In later stages symptoms may include coughing, chest pain, shortness of breath, blood in the sputum, and repeated episodes of pneumonia; weight loss, loss of appetite, impotence, and muscular weakness may also accompany the disease. Sometimes the first symptoms result from the metastasis of the tumour to other parts of the body, most notably soft extraneous tissues such as the testes.The main treatments for lung cancer are surgery, chemotherapy, and radiotherapy (The complications of radiotherapy may include vomiting, nausea, hair loss, weight loss, weakness, drop in blood levels, and skin disorders.). The choice of treatment depends on the patient's general health, the stage or extent of the disease, and the type of cancer.

Surgery is the preferred treatment for patients with non-small-cell carcinoma. Many patients, however, have heart or respiratory diseases that limit their ability to tolerate surgery. Surgery is not the main treatment for patients with cancer in both lungs or for those with metastases to distant organs. It is of no value in most cases of small-cell carcinoma; chemotherapy or radiotherapy, or both, are usually used. Small-cell carcinoma responds better to chemotherapy than do other types of lung cancer.

Treatment is most effective in the early stages of the disease, when the tumour is small and the patient is still relatively healthy. Because most patients have extensive lung cancer at the time of diagnosis, however, the outlook is generally poor. A majority of patients die of the disease within one year of its detection, and only some 10 percent survive for five years or more.Nicotine is the chief addictive ingredient in the tobacco used in cigarettes, cigars, and snuff.

In its psychoactive effects, nicotine is a unique substance with a biphasic effect; when inhaled in short puffs it has a stimulant effect, but when smoked in deep drags it can have a tranquillising effect. This is why smoking can feel invigorating at some times and can seem to block stressful stimuli at others. Nicotine is also an addictive drug though, and smokers characteristically display a strong tendency to relapse after having successfully stopped smoking for a time. When ingested in larger doses, nicotine is a highly toxic poison that causes vomiting and nausea, headaches, stomach pains, and, in severe cases, convulsions, paralysis, and death.