A substantial body of research has established that quitting smoking has immediate as well as long-term health benefits for men and women of all ages, reducing risks for diseases caused by smoking and improving health in general.1-4
The strongest evidence for this came from a landmark 50-year follow-up of 34,000 British male doctors first studied in 1951.5-7 Many participants quit as the evidence on smoking and health accumulated from the 1950s onwards, providing a natural experiment demonstrating the impact of number of years smoking on health and eventual mortality. The study showed just how hazardous tobacco is and estimated that almost two-thirds of persistent smokers were killed by their smoking. Among those who quit, the greatest benefit was seen in those who quit earliest in life.7 Quitting at age 50 halved the risk of smoking-related death, but cessation by age 30 avoided almost all of the excess risk. Stopping at age 60, 50, 40 or 30 resulted in gains, respectively, of about 3, 6, 9 or 10 years of life expectancy.7, 8 A number of more recent studies have supported these findings. A 2015 Australian study that explored tobacco smoking and all-cause mortality found that past smokers who quit prior to age 45 did not significantly differ in mortality from never-smokers. Mortality diminished gradually with increasing time since cessation. Current smokers lost an average decade of life compared with non-smokers.9 Similarly, Italian researchers found that the more cigarettes per day a person smokes, and the earlier the person quits, the more years of life gained. For men that smoked 10–19 cigarettes per day, cessation at age 30, 40, 50, or 60 led to a gain of about 7, 7, 6, or 5 years of life respectively, and for women, 5, 5, 4, or 3 years of life, respectively.10
Changes in disease risk following cessation can be measured in different ways. A common measure is relative risk, as in the studies cited above, where the likelihood of developing or dying of disease in a population of former smokers is compared to that of either current or never smokers. However this measure is influenced by the rates of disease in the reference population, which should be taken into account when examining the influence of cessation on disease risk. Another measure is absolute risk, where the actual rates of disease in former smokers are compared to those rates among current or never smokers. Rates can be directly compared, or the excess rate of disease caused by smoking in smokers can be calculated as can the excess disease rate in former smokers. Another measure is cumulative risk of disease, which enables the cumulative risk for those who quit at different ages to be compared to that of continuing smokers.
A more complete discussion of changes in risk following cessation can be found in a handbook published in 2007 by the International Agency for Research in Cancer,3 as well as a major report published in 2020 by the US Surgeon General.11 In general, the risk of disease is lower in former smokers than in otherwise similar current smokers. Smoking results in both acute and chronic changes to the body and progression towards disease. Cessation results in reversal of acute changes and slowing of disease progression and provides the potential for damage reversal.3 Smoking cessation is beneficial at any age; it reduces the risk of premature death and can add as much as a decade to life expectancy.11
Many harmful effects of smoking are arrested or begin to decline as soon as a person stops smoking.1, 2 Many disease risks in former smokers continue to decrease with prolonged abstinence, compared to continued smoking. The risk for some health effects decreases more rapidly than for others, and improvement may continue for years after quitting. Some disease risks return to the level of never smokers after a long period of abstinence, but others do not, even after 20 years of abstinence.3
The extent of damage to health and risk for smoking-related disease is related to how much the person has smoked and for how long.3 For some health effects, for example inflammation of the lung, the reversal process is not yet well understood.3 However, while some damage may be irreversible or less reversible, other problems are reversible so that there are substantial benefits to be gained from quitting at any age, regardless of smoking history.1, 2 Benefits accrue to persons both with and without smoking-related disease.1
Upon cessation, the nicotine and carbon monoxide levels in the body decline rapidly. Nicotine levels drop to very low levels within a few hours, and the main metabolites of nicotine are largely eliminated within a week.1, 3, 12 After 24 hours the level of carbon monoxide in the blood has decreased substantially.1 Smoking cessation also has far-reaching short, medium and long-term benefits for many specific health outcomes. This section summarises the benefits of quitting smoking for reducing the risk and/or progression of:
It also examines whether there are health benefits to cutting down smoking, and the health problems that may be temporarily exacerbated by quitting (but that are nonetheless outweighed by the enormous benefits of cessation).
7.1.1 Heart disease
Smoking cessation reduces the risk of cardiovascular disease and death for male and female smokers of all ages with or without existing heart disease.4 For the most common types of cardiovascular disease in Australia, the risks for smokers who quit prior to the age of 35 are comparable to people who have never smoked. In addition, smokers who quit prior to age 55 are at no greater risk of death from all major cardiovascular disease, compared to never smokers.13 A meta-analysis found that smoking cessation is beneficial for people even after the age of 65 in reducing the excess risk of cardiovascular events and mortality.14 There are immediate and long-term benefits of cessation.15 After one year the increased risk halves and after about 151, 16 to 2017 years the rate is similar to that of a non-smoker for most former smokers. However, one study found that the full extent of these cardiovascular benefits did not extend to former heavy smokers who smoked more than 3.2 packs per day, although they did have lower risk of death relative to current smokers.16
The 2020 Surgeon General’s report summarised the effects of smoking cessation on risk of cardiovascular disease and the natural history of the disease. It concluded that quitting smoking reduces levels of markers of inflammation and hypercoagulability and rapidly improves the level of high-density lipoprotein cholesterol, and reduces the risk of cardiovascular morbidity and mortality and the burden of cardiovascular disease. In patients who are current smokers when diagnosed with coronary heart disease, quitting smoking: reduces all-cause mortality; reduces deaths due to cardiac causes and sudden death; and reduces the risk of new and recurrent cardiac events.11
For specific subtypes of cardiovascular disease, quitting smoking reduces the development of subclinical atherosclerosis, and substantially reduces the risk of abdominal aortic aneurysm in former smokers compared with continuing smokers. The relative risk of coronary heart disease among former smokers compared with never smokers falls rapidly after cessation and then declines more slowly.11 The evidence to date also suggests that smoking cessation may: reduce the risk of atrial fibrillation; reduce the risk of sudden cardiac death among persons without coronary heart disease; reduce the risk of heart failure among former smokers compared with continuing smokers; lead to increased survival and reduced risk of hospitalisation for heart failure among patients with left-ventricular dysfunction; reduce the risk of venous thromboembolism; and slow the expansion rate of abdominal aortic aneurysm.11
7.1.1.1 Stroke
Quitting smoking reduces the risk of stroke morbidity and mortality.11 There is a marked reduction in risk within two to five years of quitting.3 After 15 years the risk of stroke is the same as a non-smoker.1
7.1.1.2 Peripheral vascular disease
Quitting smoking reduces the risk of peripheral arterial disease among former smokers compared with continuing smokers, and this reduction appears to increase with time since cessation.11 Quitting slows down the build-up of plaque on artery walls, so that the risk of the disease is substantially reduced. Among patients with peripheral arterial disease, smoking cessation also improves exercise tolerance, reduces the risk of amputation after peripheral artery surgery, and increases overall survival.11
7.1.2 Cancer
Smoking cessation is the only proven strategy for reducing the disease-causing processes leading to cancer.4 A large study from Japan found that even heavy smokers (more than 20 pack-years) were found to benefit from quitting smoking in terms of reducing their risk of cancer.18 The Surgeon General’s report published in 2020 concluded that smoking cessation reduces the risk of cancers of the larynx; oral cavity and pharynx; oesophagus; pancreas; bladder; stomach; bowel; liver; cervix; kidney; and acute myeloid leukemia. The evidence also suggests that quitting smoking may improve all-cause mortality in cancer patients who are current smokers at the time of a cancer diagnosis.11
7.1.2.1 Lung cancer
Quitting smoking reduces a person’s risk of lung cancer.11, 19 The relative risk of lung cancer decreases steadily after quitting, with risk decreasing to half that of continuing smokers approximately 10–15 years after smoking cessation and decreasing further with continued cessation.11 Research in the UK concluded that quitting at age 30 reduces the risk of lung cancer by several times compared to a lifetime smoker, and even quitting at 50 more than halves the risk over the next 25 years.20 The absolute annual risk of developing or dying from lung cancer does not decrease, but by stopping smoking the much greater increase in risk that would result from continuing to smoke is avoided.3
7.1.3 Respiratory diseases
Within a few months of quitting smoking, the cilia in the lungs and airways improve at sweeping mucus and debris from the lungs (as long as irreversible damage has not taken place).21 Lung function improves and the presence and severity of respiratory symptoms reduces.22 Symptoms of chronic bronchitis, such as chronic cough, mucus production and wheeze, decrease rapidly. Among people with asthma, lung function improves within a few months after stopping smoking,3, 23, 24 and smoking cessation reduces asthma symptoms and improves treatment outcomes and asthma-specific quality-of-life scores.11 Rates of respiratory infections such as bronchitis and pneumonia also decrease, compared to continued smoking.1
7.1.3.1 Chronic obstructive pulmonary disease (COPD)
Smoking cessation is the only established intervention to reduce loss of lung function over time among persons with COPD and to reduce the risk of developing COPD in smokers.11 In smokers without COPD, stopping smoking improves lung function by about 5% within a few months of cessation. The accelerated decline in lung function in smokers stops within five years of smoking cessation, returning to the far slower rates of decline that naturally occur with ageing.1, 3 Existing emphysematous damage to lung tissue caused by smoking is permanent1 however cessation slows the progression of COPD.22 Symptoms of COPD will be less likely in the short and long term.1 However, even after many years of abstinence, COPD risk still remains elevated in comparison with never smokers.1 Evidence suggests that airway inflammation in cigarette smokers persists months to years after smoking cessation.11 Statistical modelling has estimated that about 35% of the excess risk still exists after 20 years of quitting.25 In people diagnosed with COPD, stopping smoking reduces the rate of lung function decline, decreases the risk of hospitalisation for COPD,3, 21, 26 and results in fewer physician visits and less use of COPD medications.27
7.1.4 Pregnancy complications and fertility problems
The US Surgeon General has stated that ‘smoking is probably the most important modifiable cause of poor pregnancy outcome among women in the United States’1 (Refer to Chapter 3, Section 3.7 for a more detailed discussion of health effects, and Section 7.11 for a more detailed discussion of interventions aimed at pregnant women and their partners.) Stopping smoking before or during pregnancy is important and has benefits for both the foetus and the pregnant woman.28 Encouraging women to quit before they become pregnant or early in pregnancy is important because the critical period may be quite early.29
There is limited evidence that reducing consumption to fewer than eight cigarettes per day can improve birthweight30 and reduce preterm birth.31 However, complete abstinence is the only proven way to maximise health benefits. Smoking cessation by pregnant women benefits their health and that of their foetuses and newborns.11 Women who stop smoking either before becoming pregnant or in the first three to four months of pregnancy have infants with a similar birthweight to those infants born to women who have never smoked,1, 11, 32 and smoking cessation before or during early pregnancy reduces the risk for a small-for-gestational-age birth compared with continued smoking.11 Women who quit smoking before or during pregnancy may reduce their risk of pregnancy complications, including preterm premature rupture of membranes and preterm delivery (birth at less than 37 weeks gestation).1, 11, 29 Smoking cessation reduces the risk of infant death.33
Missed and painful periods are reduced after quitting, as is the risk of delayed conception.29, 34 Smoking cessation may also reduce the risk of earlier age at menopause compared with continued smoking.11 The higher risk of heart disease and stroke among women smokers who use the contraceptive pill is reduced.35
7.1.5 Oral diseases
Stopping smoking can reduce the risk of oral diseases associated with smoking including cancer, and improve the health of the mouth, gums and teeth.2, 36-38 Stopping smoking reduces the risk of leukoplakia, and after one to five years about half of leukoplakia disappears.39 Cessation reduces the risk of developing periodontitis, slows down the progress of existing disease, and quite quickly improves wound healing.2, 36, 40-45 Following cessation, gum colour gradually returns to normal37 and so-called ‘smoker’s palate’ can disappear.36 37 Stopping smoking improves the success rate of dental implants,38 and risk for tooth loss in former smokers is comparable to that of never smokers.46 Smoking cessation may be associated with relatively rapid improvement in periodontal health in young adults.42
7.1.6 Blindness
Cataract development and macular degeneration risks and progression are reduced following smoking cessation.2, 12
7.1.7 Dementia
A large cohort study from Korea examined the effect of smoking cessation on the risk of dementia. It found that compared to continuing smokers, long-term quitters and never smokers had decreased risk of overall dementia, and both long-term quitters and never smokers had decreased risk of vascular dementia compared to continuing smokers.47
7.1.8 Overall health and quality of life
Following cessation, overall health and quality of life improve, with some evidence that heavier smokers report greater improvement in quality of life after quitting and report feeling happier compared with when they were smoking.1, 2, 48-51 Ex-smokers also appear to experience a meaningful increase in subjective well-being (i.e., satisfaction with life) from quitting.52 A 2014 meta-analysis reported that smoking cessation is associated with reduced depression, anxiety, and stress, and improved positive mood compared with continuing to smoke.53 Quitting has also been linked with less financial stress among women.54
7.1.9 Other benefits of quitting
Quitting smoking at any time before surgery is advised in order to reduce the risk of postoperative complications—see Section 3.15.1.3.
There are other benefits of quitting smoking. Financial savings for a 20 cigarette pack-a-day smoker are about $7500 per year (2016 prices).55 Smokers who quit reduce their likelihood of financial stress and are likely to enhance their material wellbeing.56 As more public and private places become smokefree, ex-smokers avoid the inconvenience of having to find somewhere to smoke. Quitting avoids further smoking-related damage to skin, and slows the development of wrinkles.57 Life insurance is often cheaper,58 the risk of smoking-related fires is reduced59, 60 and people who quit have fewer sick days (see also Section 17.2).2
7.1.10 Cutting down: are there health benefits?
Cutting down the number of cigarettes smoked each day is a common strategy used by smokers to reduce harm, to move towards quitting, or to save money.61-64 However, research shows no noticeable improvement in health outcomes or lifespan among smokers who are able to cut down on a long-term basis.4, 65-67 This is largely because smokers primarily seek a consistent level of nicotine. Those who cut down therefore tend to smoke the remaining cigarettes harder by taking more and larger puffs, and holding each puff longer. Thus they do not reduce their intake of toxins as much as the reduction in the number of cigarettes suggests.62, 68 For a detailed discussion on smoking reduction, see Chapter 18, Section 18.3.
7.1.11 Health problems that may be temporarily exacerbated by quitting
While there is no question of the overall long-term benefits of cessation, quitting is associated with a number of bothersome short-term problems such as mouth ulcers and cold symptoms, weight gain and constipation.22
7.1.11.1 Mouth ulcers and colds
There is evidence that smokers and users of smokeless tobacco are less likely to develop aphthous stomatitis (common mouth ulcers). Individuals commonly report a short-term increase in mouth ulcers and cold symptoms on quitting smoking.69
7.1.11.2 Diabetes
People with diabetes who quit smoking have a lower risk of death and cardiovascular events compared with those who continue to smoke.70 However, recent research has shown while quitting generally decreased the risk of diabetes overall, smoking cessation is associated with an increased risk and deterioration in blood glucose control in the first 2–3 years of abstinence.71, 72 Smoking cessation can cause weight gain and can be associated with diabetes or obesity onset,73, 74 however results of research to date are mixed regarding the overall relationship between quitting and diabetes.75 It is important that quit attempts are accompanied by preparation, extra care, and careful monitoring to keep the person’s blood glucose well controlled during this time.71, 76
7.1.11.3 Quitting and weight gain
While smoking cessation usually results in some level of weight gain, there is disagreement about the extent and how long it lasts.
Smokers’ average weight is about 3 to 4 kg less than that of non-smokers.77, 78 Smoking appears to attenuate weight gain over time, in part due to increasing metabolic rate.29, 78 The difference in weight between smokers and non-smokers is more marked in older long-term smokers while the average weight of younger smokers is similar.29, 79-81 The weight difference, however, is further complicated by the finding that despite their lower weight and body mass index (BMI), smokers have a greater waist-to-hip ratio than non-smokers. Increased waist circumference is a stronger predictor of cardiovascular disease than BMI.82
When smokers quit, the majority experience some weight gain.1 Estimates of weight gain associated with cessation vary depending on the sample, study design and follow-up period.83 Most excess weight gain occurs in the first year after cessation, after which the rate of weight gain slows.78, 79, 84-88 One study found that increase in body weight may continue for longer.89 Estimates of the mean weight gain in people continuously abstinent for a year are about 5 to 6 kg.85-88 Results from a 2015 meta-analysis showed that on average, quitters gained 4.1 kg and continuing smokers gained 1.47 kg over an average of 5.15 years follow-up.90 Individual experience of weight change after quitting is quite broad, ranging from weight loss to a minority gaining over 10 kg.79, 86, 88, 91-94 Increase in waist circumference per kilogram gained is smaller in people who quit than in continuing smokers, indicating that recent ex-smokers gain less visceral fat.92, 95
Limited research suggests that some of the weight gained during the first few years after quitting may be lost with continued abstinence,96, 97 however more research is needed to resolve this issue.98 Large cross-sectional studies show that long-term former smokers have a mean waist-to-hip ratio and a mean BMI similar to or approaching that of people who have never smoked.82, 91 94, 99 Research in New Zealand that followed a cohort of people from age 15 to 38 concluded that on average, quitters do not experience greater weight gain than never-smokers.100
Reasons for the association between smoking cessation and weight gain are not fully understood. Predictors of weight gain include younger age, lower socio-economic status and heavier smoking, with some influence of underlying genetic factors.84 Weight gain after smoking cessation is related to a transient increase in food intake,101 changes in metabolic rate,102 and minimal physical activity.103, 104 There is some evidence that smoking and obesity are independently associated with specific food cravings and mood states.105 Smokers who have a higher BMI also experience more weight gain after quitting.106, 107 A person’s gender may also influence post-cessation weight gain. One study found that among light smokers, men gained more weight on average than women one year after quitting, while the opposite was observed among heavy smokers. Young women who were heavy smokers had the highest risk of weight gain after quitting.108
The health benefits of smoking cessation far outweigh the health risk from extra body weight, unless the weight gain is extraordinarily large.1 Even in cases of significant post-cessation weight gain and/or high prevalence of obesity, diabetes, and hypertension, sustained tobacco abstinence appears to substantially reduce cardiovascular risk.74, 109-111 The risk of death is smaller in overweight or obese ex-smokers than in normal-weight smokers.112 One study concluded that cessation related weight gain may actually be beneficial, as it is associated with increased muscle mass, muscle strength, and bone density.113 Nonetheless, fear of weight gain is a significant factor in discouraging quitting and provoking relapse in smokers.84, 114-122 Pharmacological treatment with medications such as nicotine replacement therapy and varenicline may be useful to suppress weight gain during smoking cessation.123, 124 (See Chapter 3, Section 3.29 for further information on the health effects of smoking in conjunction with and compared with those associated with obesity, and Section 7.8.5 for further information on managing weight gain.)
7.1.11.4 Mental health problems
Many smokers appear to have an increase in depressed mood and associated negative affect as part of nicotine withdrawal, but for the majority of people who quit this is temporary.77, 125 A common belief is that smoking cessation will exacerbate mental illness.126 However, recent evidence suggests that the reverse is true; quitting smoking for at least six weeks actually improves mental health, mood, and quality of life, both among the general population and among people with a psychiatric disorder.53 (See Section 9A.3)
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References