Although the health risks associated with smoking are well known, almost 45 million Americans continue to smoke. The younger you were when you began smoking, the greater your risk of suffering these negative health effects. Quitting smoking is, without a doubt, the single best thing you can do for your health.

Every time you smoke a cigarette, you inhale more than 4,000 chemicals. Interestingly, many people think nicotine is tobacco's most harmful ingredient. Although nicotine is the addictive substance in tobacco and has many negative health effects, it is not necessarily the one that causes the most harm to your health. Many of the health consequences associated with tobacco use result from the tars, carbon monoxide and carcinogens (cancer-causing chemicals) in cigarette smoke.

Below is just a partial list of health complications in which smoking is a key player. Keep in mind that smoking is responsible for approximately 440,000 deaths (about one in every five deaths) per year in the United States. It is the leading cause of preventable illness in this country.

Smoking accounts for approximately 80% of all cases of lung cancer, the leading cause of cancer death in the United States. Because smokers inhale toxins from cigarette smoke directly into their lungs, their risk of lung cancer is 13 times greater than nonsmokers' risk.

Smokers are also at increased risk of throat cancer. The single best way to prevent this disease is to stop smoking.

About 90% of people diagnosed with oral cancer use tobacco products. The risk of this cancer increases with the amount and duration of tobacco use.

Tobacco users are at increased risk of esophageal cancer. The risk increases with the amount and duration of tobacco use.

Cigarette smoking is the single most significant risk factor for bladder cancer. Smokers have two to four times greater risk for this disease compared with nonsmokers.

Cigarette smoking is the single most preventable risk factor for pancreatic cancer.

Tobacco use may contribute to cervical cancer.

More than 80% of all cases of chronic bronchitis (inflammation of the breathing passages) are caused by cigarette smoking. You dramatically reduce your risk when you quit. Secondhand smoke is also a factor in chronic bronchitis.

Cigarette smoking accounts for more than 90% of all cases of emphysema (destruction of the air sacs in the lungs). You can lower your risk of this disease if you stop smoking.

Smoking is a preventable cause of chronic laryngitis (inflammation of the vocal cords). Cigarette smoke irritates the throat, triggering this problem.

The risk of stroke (inadequate blood flow to the brain) is increased in anyone who smokes.

Smoking contributes to your long-term risk of a heart attack, as well as to your immediate risk of a heart attack. It not only causes damage to heart arteries, but it also makes you more likely to form a blood clot that can trigger a heart attack. Your risk of heart attack is significantly increased if you smoke.

Cigarette smoking is a risk factor for coronary artery disease (the build up of fatty deposits in the arteries that supply blood to the heart).

Your risk of aortic aneurysm (a weakness and bulging of the wall of your largest artery) is increased if you smoke. An aortic aneurysm can cause fatal internal bleeding if it ruptures.

Smoking increases your risk of peripheral vascular disease (poor circulation). If you already have peripheral vascular disease, smoking causes additional artery damage and exacerbates your symptoms. Peripheral vascular disease can cause leg or buttock pain with walking. It can also lead to leg ulcers, foot ulcers or gangrene and may require amputation of toes, the foot or the lower leg.

Smoking reduces bone density. This puts you at risk of osteoporosis (thin bones).

Hip fracture is most often related to osteoporosis, a condition worsened by smoking.

Smoking supersedes any other risk factor for gum disease. And it takes longer for gum disease to heal in smokers.

Smokers are twice as likely as nonsmokers to lose their teeth.

Smokers are at greater risk of developing macular degeneration, a leading cause of vision loss.

The risk of cataracts (clouding of the lens) is 40% higher in smokers than in nonsmokers.

Smoking can contribute to fertility problems in both men and women.

Smoking during pregnancy increases the risk of fetal death and is a leading cause of below-average weight at birth.

Smoking can increase the frequency of heartburn and can worsen the symptoms of gastroesophageal reflux disease (a digestive disorder in which stomach acid enters and irritates the esophagus).