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An in-depth report on the health risks of smoking and how to quit.

Alternative Names

Nicotine Replacement

Risk Factors

Tobacco, mostly cigarette smoking, kills more than 440,000 people a year, making it more lethal than AIDS, automobile accidents, homicides, suicides, drug overdoses, and fires combined. Indeed, one in every five deaths is attributable to smoking. It reduces life expectancy by 15 to 25 years and is the single most preventable cause of death. In one study, only 42% of male lifelong smokers reached the age of 73, compared to 78% of nonsmokers. Smoking may be even more dangerous in women. Smoking may be even more dangerous now than 30 years ago, most likely because the lower tar and nicotine levels in most cigarette brands cause people to inhale more deeply.

Even cutting back smoking by more than half does not cut the risk for poor health compared to heavy smokers (considered to be more than 15 cigarettes a day). Only quitting helps.

Harmful Chemicals in Cigarette Smoking. The smoke is the most dangerous component of the cigarette. Smoke contains nitrogen oxide and carbon monoxide, which are harmful gases. When people inhale they also bring tar into their lungs. Tar itself includes 4,000 chemicals, some of which are known to cause cancer. Other inhaled chemicals include:

  • Cyanide.
  • Benzene.
  • Formaldehyde.
  • Methanol (wood alcohol).
  • Acetylene (the fuel used in torches).
  • Ammonia.

Experts warn that so-called safer cigarettes (e.g., Advance, Omni), which claim to filter out some of these toxins, are still not safe, as the smoke from these cigarettes still contain many harmful chemicals. Even worse, a 2002 study suggested that people who smoke as few as three standard brand cigarettes a day are at higher risk for blood vessel abnormalities that endanger the heart.

Click the icon to see an image of a tobacco plant.

Cigars and Pipes. One study reported that people who switch from cigarettes to cigars or pipes halve their risk of lung cancer, heart disease, and chronic lung disease, possibly because they use less tobacco and inhale less. Still, the risk of these diseases using "safer" forms of tobacco is 50% to almost 70% higher than nonsmokers. And the risk for periodontal disease and tooth loss may be just as high in pipe and cigar smokers as it is in cigarette smokers.

Gingivitis is an inflammation of the gums caused by plaque and bacteria accumulation.

Effects of Second-Hand Smoke

The effects of second-hand smoke, or passive smoking, has been debated and widely studied, but they are still not entirely clear. Major organizations, including the American Heart Association and US Surgeon General have stated that passive smoke poses a 30% increase in the risk of heart disease. One analysis of studies suggested that exposure to second-hand tobacco smoke may increase the risk of lung cancer in the nonsmoker by about 25%. The Environmental Protection Agency has classified second-hand smoke as a carcinogen.

Nevertheless, there is some evidence that second-hand smoke may not be as harmful to adults as most people believe. A major 2003 study in California on smokers and their spouses, in fact, found no significant relationship between second-hand smoke and a higher risk for tobacco-related deaths, heart disease, or lung cancer. A 2000 study suggested that the numbers suggesting a high risk for lung cancer from passive smoking may be overstated, because they were derived from many small and possibly biased studies. Some experts believe that studies showing a positive association between poor health and passive smoke may be more likely to be published than negative ones.

Discovering that passive smoking may not be as dangerous as currently believed in adults is not an argument to restore smoking in public areas where it is currently banned. Tobacco smoke is unpleasant for most nonsmokers and any public efforts to discourage smoking in active smokers should be applauded.

Moreover, harmful effects of parental smoking on children have been fairly well established. Smoking in pregnant women and new mothers is strongly linked to low birth weight and sudden infant death syndrome (SIDS). A body of research continues to suggest that exposure to environmental smoke in the home increases a child's risk for lower respiratory tract infections and asthma.

Effects of Smoking and Quitting on Heart Disease, Diabetes and Stroke

Smokers in their thirties and forties have a heart-attack rate that is five times higher than their nonsmoking peers.

Click the icon to see an image of an acute myocardial infarction.

Any current smoker is at higher risk for heart disease or stroke. Although heavy smokers--particularly those who smoke high-tar cigarettes--are at highest risk, a 2002 study indicated that even light smokers (as few as three cigarettes a day for women and six for men) doubled their risk of heart attack.

Smoking poses greater risks in women than in men. For example, in women who smoke, the risk for a heart attack is about 50% greater than in male smokers. In women over 35 who smoke, taking oral contraceptives poses special hazards by increasing their risk for heart attack and stroke well beyond their non-smoking peers.

Specific Effects of Smoking on the Heart. Cigarette smoking may be directly responsible for about 62,000 deaths from heart disease each year. Smoking cigars may increase the risk of early death from heart disease, although evidence is much stronger for cigarette smoking. The damaging effects of smoking on the heart are multifold:

  • Smoking lowers HDL levels (the so-called good cholesterol), even in adolescents. After a person quits, HDL levels increase.
  • It causes stiffness and inflexibility in blood vessels. One way it does this is by reducing levels of nitric oxide (NO), a substance in the lining of blood vessels that keeps them supple and promotes cardiovascular health.
  • It increases the risk for blood clots. In fact, smoking may cause larger blood clots, which can increase the severity of heart attacks.
Click the icon to see an image of a blood clot.
  • It increases the activity of the sympathetic nervous system (which regulates electrical activity in the heart and blood vessels).
  • In women, it may increase heart disease risk by altering hormone levels and causing estrogen deficiency.

Quitting will rapidly reduce the risk of developing heart disease.

Although long-term smoking may still permanently damage arteries, a major 2003 analysis reported that when patients with heart disease quit, their mortality rates were reduced by 36% compared to patients who continued to smoke.

Effects of Smoking on Diabetes. A study of women smokers found that those with type 2 diabetes were at especially high risk for heart disease. Quitting smoking reduced this risk substantially. Smoking may also accelerate other complications of diabetes, including kidney disease.

Effects of Smoking on Stroke. Smoking can affect blood vessels in the brain as it does in the heart. People who smoke a pack a day have almost two and a half times the risk for stroke as nonsmokers. The risk for stroke may remain elevated for as long as 14 years after quitting. Note: women smokers who take oral contraceptives have a specifically higher risk for stroke. In fact, any woman who smokes increases her risk for hemorrhagic stroke, the type of stroke caused by a ruptured blood vessel.

The Effects of Smoking and Quitting on Cancer

Smoking accounts for about 30% of all cancer deaths in the US, and it has been cited as the most important factor in changes in worldwide cancer trends.

Click the icon to see an image of the hazards of smoking.

Lung Cancer. Smoking is the primary risk factor in 85% to 90% of lung cancers, which is expected to kill nearly 155,000 Americans in 2002. About 15% of all people who smoke develop lung cancer, with the risk varying depending on the duration of the addiction and the number of pack years. (A pack year equals the number of packs of cigarettes smoked per day multiplied by the number of years that the person has smoked.)

Risk for Lung Cancer After Quitting in Men at Age 75

Quitting Age










Source: Smoking, smoking cessation, and lung cancer in the UK since 1950: combination of national statistics with two case-control studies, British Medical Journal. 321:323-329 (5 August 2000)

The table referred to is from a study of male smokers. Some studies indicate that the risk for lung cancer may be even higher in women smokers. In a 1999 study, the risk for older women was 2.3 times that of older men. Death rates from lung cancer among Caucasian American women increased by 600% between 1950 and 2000, Each year, in fact, lung cancer now kills over 60% more women than breast cancer does and accounts for 25% of all cancer deaths in women.

Some evidence suggests that people who smoke low-tar, or light, cigarettes may be no safer than those who smoke high-tar cigarettes. People who smoke low-tar cigarettes tend to inhale more deeply, bringing particles to the smallest and most vulnerable tissues in the lungs where these cancers start. In fact, these smokers may have a higher risk for a particularly deadly form of lung cancer called adenocarcinoma.

Mentholated cigarettes have also been associated with a higher risk for lung cancer, although a 2003 study failed to find any differences in risk compared to nonmenthol brands.

Other Cancers. Smoking is also related to other cancers:

  • Smoking and smokeless tobacco also cause between 60% and 93% of cancers of the oral passages and upper airways, including the throat, mouth, and esophagus.
Click the icon to see an image of tobacco and cancer.
  • Smoking triples the risk of skin cancers.
Click the icon to see an image of a basal cell skin cancer.
  • Although smoking does not appear to affect a risk for developing breast cancer itself, it does appear to increase the severity of existing breast cancer, possibly because of a higher risk for the cancer to spread to the lungs.
  • Smokers have higher rates of leukemia and cancers of the kidney, stomach, pancreas and bladder (the risk for bladder cancer may be higher in women smokers than in male smokers).
  • Studies have found a link between long-term smoking and an increased risk for colon and rectal cancer.
Click the icon to see an image of colon cancer.
  • About 30% of cervical cancers have been attributed to both active and passive smoking.
Click the icon to see an image of cervical cancer.

Biologic Effects of Smoking That May Contribute to Cancer. Cigarette smoke contains many chemicals and cancer may develop from the accumulative effects of more than one.

Click the icon to see an image of adenocarcinoma.
Click the icon to see an X-ray of adenocarcinoma.
  • The smoke is the most dangerous component of the cigarette. Chemicals formed during smoking trigger genetic mutations that lead to cancer. When people inhale it, they bring tar into their lungs that itself includes 4,000 chemicals, some of which are carcinogenic. Other inhaled chemicals in cigarette smoke that may increase the risk for cancer include cyanide, benzene, formaldehyde, methanol (wood alcohol), acetylene (the fuel used in torches), and ammonia. Smoke also contains nitrogen oxide and carbon monoxide, both of which are harmful gases.
  • Nicotine itself may be a hazard. A 2000 laboratory study suggested that the human body might be converting inhaled nicotine into a chemical called aminoketone, which has been linked to the formation of tobacco-related lung cancer. And another 2001 study reported that nicotine triggered new blood vessel growth, which could theoretically promote growth of any existing tumors. Whether or not these studies apply to long-term use of nicotine replacement products (such as patches), as well as from cigarette smoking, is still unclear. (They should certainly not discourage people from using nicotine replacement methods for quitting, but may indicate that these devices should not be used long-term.)
  • Chromosomal damage in the lung occurs in nearly all chronic smokers. An elevated risk for lung cancer can persist for more than 20 years after quitting smoking, although the risk drops significantly even in the first year after quitting.

The Effects of Smoking and Quitting on Acute and Chronic Lung Diseases

Smoking is associated with a higher risk for nearly all major lung diseases, including pneumonia, flu, bronchitis, and emphysema. There is also a link between smoking and exacerbation of asthma symptoms. Second-hand smoke, too, has been associated with respiratory problems, including nighttime chest tightness, breathlessness after exertion, and worsening of asthma.

Click the icon to see an image of emphysema.

Quitting almost immediately improves lung function. Some evidence also suggests that benefits for the lungs are even more significant for women who quit than for men. One study indicated that smokers who quit and start again may damage their lungs even more severely than people who have not yet made an attempt to quit. Such people, however, may simply be more strongly addicted than other smokers and may inhale more deeply and hold the smoke in their lungs longer. The message here is not that quitting smoking is more dangerous than not quitting; rather, the emphasis is on not starting again.

Dementia and Neurologic Diseases

The role between smoking and neurologic diseases has been mixed. Nicotine has some positive effects on the brain, including improving concentration and short-term memory. Certainly, smoking can increase the risk for dementia by causing small or major strokes. Low levels of HDL (good cholesterol), which are more common in smokers, have also been linked to dementia.

Click the icon to see an image of stroke.

Parkinson's Disease. Cigarette smokers appear to have a lower risk for Parkinson's disease, indicating some protection by nicotine. This finding, of course, is no excuse to smoke, but such protection may help researchers develop new therapies.

Alzheimer's Disease. Nicotine enhances the actions of the cholinergic system (which is depleted in Alzheimer's disease) and is known to improve concentration and memory in the short term. Some studies have suggested that nicotine may protect nerve cells and help prevent the formation of beta amyloid. One study indicated that nicotine might help protect against Alzheimer's disease in carriers, but not noncarriers, of the ApoE4 gene. Research to date, however, has found no strong evidence of improvement with nicotine replacement methods. Smoking itself makes little difference in the risk for Alzheimer's, and, in fact, the risk for dementia is slightly higher in smokers.

Effect on Male Sexuality and Reproduction

Smoking also negatively affects male sexuality and fertility. Heavy smoking is frequently cited as a contributory factor in impotence in men because it decreases the amount of blood flowing into the penis. One study noted, for example, that among men with high blood pressure, smoking causes a 26-fold increase in impotence.

Smoking also affects fertility. It impairs sperm motility, reduces sperm lifespan, and may cause genetic changes that affect the offspring. One 2002 trial found that men or women who smoke have lower success rates with fertility treatments. An earlier study reported that men who smoke also have lower sex drives and less frequent sex.

The Effects of Maternal Smoking on Fertility, Pregnancy, and Children

Studies have now linked cigarette smoking to many reproductive problems. Women who smoke pose a greater danger not only to their own reproductive health but, if they smoke during pregnancy, to their unborn child. Continuing to smoke also may cause health problems in the growing child.

Female Infertility. Some of the negative effects of smoking on female fertility include the following:

  • Greater risk for infertility. Women at greatest risk for fertility problems are those who smoke one or more packs a day and who started smoking before age 18.
  • Earlier menopause. Women who smoke tend to start menopause at an earlier age than nonsmokers, perhaps because toxins in cigarette smoke damage eggs.
  • Greater risk for ectopic pregnancy and miscarriage.
Click the icon to see an image of an ectopic pregnancy.

One intriguing study found that mothers or fathers who smoke a pack or more a day are more likely to have daughters than sons. The likelihood of having a male child was lowest when both parents smoked.

Effects on Unborn Child. Smoking during pregnancy is harmful to an unborn child in many ways:

  • Pregnant women who smoke increase the risk for stillbirth, prematurity, and low birth weight in their babies. Infant mortality rates in pregnant smokers are increased by 33%, mostly because of low birth rate. Some women carry particular genes that may make it especially likely that they will deliver low birth weight infants if they smoke, although newborns of all female smokers have a greater risk for low weight. The good news is that women who quit before becoming pregnant or even during the first trimester reduce the risk for a low birth weight baby to that of women who never smoked.
  • Children of mothers who smoke during pregnancy may also be at increased risk for obesity and diabetes.
  • Smoking reduces the mother's folate levels, a B vitamin that is important for preventing birth defects.
  • A 2003 study also suggested that smoking during pregnancy can have harmful neurologic effects on newborns, and, furthermore, these infants may have to endure withdrawal symptoms after birth.

Unfortunately, the standard cessation aids (nicotine replacement, antidepressants) are not appropriate for pregnant women. Women who want to become pregnant should use these aids before they try to conceive and make all attempts to quit.

Effects of Second-Hand Smoke on Children. An estimated four million children a year fall ill from exposure to second-hand smoke. Parental smoking has been shown to affect the lungs of infants as early as the first two to 10 weeks of life, and such abnormal lung function could persist throughout life.

A number of studies have reported associations between smoking parents and childhood illnesses.

  • Parental smoking is believed to increase the risk for lower respiratory tract infections (such as bronchitis or pneumonia) by 50%. Environmental exposure to smoke is thought to be responsible for 150,000 to 300,000 such cases of such every year.
  • Exposure to second-hand smoke in the home increases the risk for asthma and asthma-related emergency room visits in children who have existing asthma.
  • Smoking in pregnant women and new mothers is strongly linked to sudden infant death syndrome (SIDS) in their children.
  • Parental smoking has been linked to recurrent ear infections and eczema.

If new mothers cannot quit, they should be sure not to smoke in the same room as their infant. This simple behavior can considerably reduce the risks to the child.

Note: Of some encouragement is the fact that in one study, people who had been exposed to tobacco smoke as children did not appear to have any higher risk for lung cancer later on.

Effects on Bones and Joints

Smoking has many harmful effects on bones and joints:

  • Smoking impairs formation of new bone, and women who smoke are at high risk for loss of bone density and osteoporosis.
Click the icon to see an image of osteoporosis.
  • Postmenopausal women who smoke have a significantly greater risk for hip fracture than those who do not.
  • Smokers are more apt to develop degenerative disorders and injuries in the spine.
  • Smokers have more trouble recovering from surgeries, including knee or hip replacements.
  • Smokers whose jobs involve lifting heavy objects are more likely to develop low back pain than nonsmokers.
  • In women, smoking may also pose a small increased risk for developing rheumatoid arthritis. Women smokers or ex-smokers who have rheumatoid arthritis, especially those with a particular genetic makeup, may also have a more severe form of the disease.
Click the icon to see an image of rheumatoid arthritis.

The Effects of Smoking on the Gastrointestinal Tract

Smoking increases acid secretion in the stomach. It also reduces blood flow and production of compounds that protect the stomach lining.

Diverticulitis. A 2000 study suggested that smoking was a major risk factor in diverticulitis, a condition in which small out-pouches develop in the wall of the colon. In addition, smokers were at risk for its complications, including bleeding and abscess. Diverticulitis mostly affects people over 50 years of age.

Inflammatory Bowel Disease. Smoking has mixed effects on inflammatory bowel disease.

Click the icon to see an image of inflammatory bowel disease.

Smokers have lower than average rates of ulcerative colitis, but higher than average rates of Crohn's disease. In fact, smokers with Crohn's disease who quit experience a much less severe course.

Peptic Ulcers. Results of studies on the effect of smoking on ulcers are mixed. Some evidence suggests that smoking delays the healing of gastric and duodenal ulcers. One 1999 study reported that after ulcers healed, about half of smokers relapsed after a year and that all heavy smokers relapsed after three months. Other studies, however, have found no increased risk for ulcers in smokers, and smoking does not appear to increase susceptibility to H. pylori, the bacteria that causes many peptic ulcers. This should not give smokers any comfort, however, given the proven dangers from smoking.

Click the icon to see an image of peptic ulcers.

Hepatitis and Cirrhosis. Smoking is linked to increased liver scarring (cirrhosis) caused by either excessive drinking or chronic hepatitis B or C viruses.

The Effects of Smoking on the Thyroid and Autoimmune Conditions

Hyper- and Hypothyroidism. Cyanidem, found in tobacco smoke, interferes with thyroid hormone production. Smoking triples the risk for developing thyroid disease, particularly autoimmune hyper- and hypothyroidism. Women smokers with subclinical hypothyroidism, a symptom-free condition in which the thyroid gland is mildly underactive, face an increased risk for developing full-blown hypothyroidism than their nonsmoking peers. Smoking may also increase the negative effects of hypothyroidism on the heart. Smoking has also been linked to goiter, a swelling of the thyroid that occurs in people who dont get enough iodine.

Click the icon to see an image of the thyroid.

Other Autoimmune Diseases. One study reported that smokers are almost seven times more likely to develop SLE than nonsmokers, and ex-smokers have a 3.6-fold risk, according to research published in 2001. Not all studies support the association.

The Effects of Smoking on Surgical Recovery

Smokers are at increased risk for heart and circulatory problems and delayed wound healing after surgery. In one study, patients who were able to cut down or quit smoking six to eight weeks prior to knee or hip replacement surgery were much less likely to suffer complications.

The Effects of Smoking on Other Disorders Related to Aging

People who smoke also endanger other parts of their bodies as they age. The following are age-related conditions that occur at higher rates in smokers than nonsmokers:

  • Cataracts, importantly the type of cataract that most severely limits vision. Quitting smoking lowers the likelihood of needing cataract surgery in the future, although not to the level seen with nonsmokers.
Click the icon to see an image of a cataract.
  • Macular degeneration, a leading cause of blindness in older people.
  • Gum disease, and therefore tooth loss.
  • Wrinkles. Studies in multiple ethnic groups confirm that smokers are nearly five times more likely to develop more and deeper wrinkles as they age compared to nonsmokers.
  • Baldness and premature gray hair.
  • Hearing loss, particularly high-frequency hearing loss. Some experts believe that losing the ability to hear high pitched sound in smokers may be due to a decrease in blood flow to the cochlea, the part of the ear that carries sound to the brain.
  • Incontinence. One study of 600 women indicated that smokers and former smokers are twice as likely to develop incontinence than women who never smoked.

Physical Benefits After Quitting

Time after last cigarette

Physical Response

20 minutes

Blood pressure and pulse rates return to normal.

8 hours

Levels of carbon monoxide and oxygen in the blood return to normal.

24 hours

Chance of heart attack begins to decreases.

48 hours

Nerve endings start to regrow; ability to taste and smell increases.

72 hours

Bronchial tubes relax; lung capacity increases.

2 weeks to 3 months

Improved circulation; lung function increases up to 30%.

1 to 9 months

Decreased incidence of coughing, sinus infection, fatigue, and shortness of breath; regrowth of cilia in the airways, increasing the ability to clear mucus and clean the lungs and reducing the chance of infection; overall energy level increases.

Long-Term Effects of Quitting

After a year, risk of dying from heart attack and stroke is reduced by up to half.


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