A major reason for the spread and popularity of tobacco since the sixteenth century is connected to one of its short-term effects on the human body. An important active ingredient in tobacco smoke is nicotine, which is rapidly delivered into the bloodstream through the lungs. Nicotine is then transported to receptors in the central nervous system, increasing heart rate and the release of dopamine, a pleasure-inducing chemical. Tobacco smoke also contains chemical substances that increase heart rate and elevate blood pressure, sometimes causing dizziness and tremors because of a reduced flow of oxygenated blood to the brain and extremities.
Smoking also has short-term effects on the respiratory and digestive systems. Research on animals and humans has demonstrated that inhaling smoke from cigarettes impairs pulmonary clearance, which can lead to coughing and increased susceptibility to colds and allergens. Smoking attenuates the functioning of the lung’s cilia and alveoli, reducing the lung’s ability to oxygenate blood.
Also, extensive research has been done on the immediate effects of smoking during pregnancy and the multiple harmful chemicals in cigarette smoke on the fetuses of animals and humans. These chemicals cause such effects as changes in fetal heart rate and placental circulation and metabolism; a rise in carboxyhemoglobin concentrations; and a host of other problems, which have led to a series of warnings that pregnant women should not smoke.
Extensive research has shown that habitual smoking dramatically increases the risk for arteriosclerosis and coronary heart disease. General agreement exists that acute and chronic cardiovascular effects of smoking can be largely attributed to nicotine. Smoking also has been associated with narrowing of the blood vessels in the heart, brain, and other organs, significantly increasing the chances of stroke.
Evidence shows a causal relationship between smoking and lung cancer, and that smokers are more than ten times as likely as nonsmokers to have lung cancer: roughly 80 to 90 percent of lung cancer cases continued to be caused by smoking. Furthermore, habitual smoking has been associated with increased susceptibility to such chronic obstructive pulmonary diseases (COPD) as emphysema and bronchitis. According to the US Centers for Disease Control and Prevention (CDC), men who smoke increase their risk of dying from bronchitis and emphysema by seventeen times.
Because smoking reduces the effectiveness of the body’s immune system, habitual smokers readily have a variety of respiratory infections, including pneumonia. Other research has established a causal relationship between smoking and cancers of the digestive and urinary systems. For example, smokers are much more likely to develop and to die from mouth and throat cancers, stomach cancers, colorectal cancer, pancreatic cancers, bladder cancer, and kidney cancer.
Much research has been devoted to studying the long-term health effects of smoking on the reproductive system. These studies have revealed negative effects from fertilization to birth. Smoking causes lowered fertility; stunted fetal growth; increased likelihood of miscarriages, premature births, and stillbirths; and complications for normal-term births. Women who are habitual smokers also give birth to babies with low birth weights, and the harmful chemicals in the bodies of breastfeeding mothers who are smoking can be passed to their babies, causing immediate and long-term damage. The reproductive systems of men also are affected by smoking, with reduced sperm count and increased impotency the most commonly reported problems.
