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Tobacco, smoking and cancer: the evidence

This page contains information about the links between smoking and cancer. Click on the links below to read about specific topics.

• Smoking and cancer deaths
• Lung cancer
• Number of cigarettes and time spent smoking
• Other cancers
• The benefits of quitting
• Chemicals in a cigarette
• Low-tar cigarettes
• The effects of alcohol
• Second-hand smoke
• Children and second-hand smoke
• Pregnant women
• Smokeless tobacco

You can find out more about the evidence behind other health topics in our other How do we know? pages.

Smoking is the single biggest cause of cancer in the world

Experts agree that smoking is the single biggest cause of cancer in the world 1-3. Smoking causes over a quarter of cancer deaths in developed countries 4.

Around half of current smokers will be killed by their habit if they continue to smoke. And 25-40% of smokers will die in middle age 5-6

Smoking causes even more deaths from other respiratory diseases and heart conditions than from cancer 2. If current trends continue, scientists estimate that tobacco will kill about one billion people in the twenty-first century 2.

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Smoking greatly increases the risk of lung cancer

Studies from Europe, Japan and North America have shown that 9 in 10 lung cancers are caused by smoking 2,7. In 2002, lung cancer killed around 33,600 people – about one person every 15 minutes 8.

Tobacco smoke was first shown to cause lung cancer in 1950 9. This study found that people who smoked 15-24 cigarettes a day were 26 times more likely to die from lung cancer than lifelong non-smokers. Even people who smoked less than 15 cigarettes a day were still 8 times more likely to die from lung cancer than life-long non-smokers.

After these first results came out, UK scientists began a large study of smoking in British doctors, which Cancer Research UK has helped to fund 10. This British Doctors’ Study has provided much of our current knowledge about the dangers of smoking.

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The people with the highest lung cancer risks are those who:

• smoke the most cigarettes per day
• smoke over long periods of time, and
• start smoking young

We cannot exactly calculate a person’s lung cancer risk based on how many cigarettes they smoke or the number years they have been a smoker. But studies have shown that lung cancer risk is greatest among those who smoke the most cigarettes over the longest period of time 2.

The length of time spent smoking seems to be the more important of these two factors. The British Doctors’ Study found that people who had smoked for 45 years had 100 times the lung cancer risk of people who had smoked for 15 years, regardless of whether they smoked heavily or moderately 11. And smoking one packet a day for 40 years is about 8 times more dangerous than smoking two packets a day for 20 years 8.

Even light or irregular smoking can increase the risk of cancer. One study found that even people who smoked 1-4 cigarettes a day still had much greater risks of dying from lung cancer or heart disease 12. And the EPIC study found that occasional smokers who have never smoked daily, still have higher risks of most cancers, and double the risk of bladder cancer.13

Starting smoking at an early age increases the risk of cancer even more. One study found that young smokers are especially vulnerable to DNA damage caused by chemicals in cigarette smoke. And when they quit, they have higher levels of DNA damage than people who started smoking later in life 14.

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Smoking is a major cause of several types of cancer

Smoking also increases your risk of cancers of the bladder, cervix, kidney, larynx (voice box), mouth, oesophagus (foodpipe), pancreas, stomach, liver and some types of leukaemia 2,3. As with lung cancer, most of these risks increase with the number of cigarettes smoked and the number of years spent smoking 2.

• Smoking is the most important preventable cause of bladder cancer and causes two in three cases in men and one in three cases in women. It increases the risk of this disease by 3-5 times.15.
• Smoking doubles the risk of kidney cancer, and causes one in four cases in men, and one in ten cases in women 16.
• Smoking is the number one cause of mouth and oesophageal cancers, and together with alcohol, causes about nine in ten cases of these cancers.17
• Smoking is the only established preventable cause of pancreatic cancer, one of the most dangerous types of cancer in the UK. It causes over a quarter of pancreatic cancer cases.

There is some evidence to suggest that smoking may increase the risk of breast cancer, bowel cancer and lymphomas but more research will be needed to say for sure.18-21

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Stopping smoking can reduce your risk

A large number of studies have shown that stopping smoking can greatly reduce the risk of smoking-related cancers 2. And the earlier you stop, the better. The last results from the Doctors’ Study show that stopping smoking at 50 halved the excess risk of cancer overall, while stopping at 30 avoided almost all of it 10.

However, it’s never too late to quit. One study found that even people who quit in their sixties can experience health benefits and gain valuable years of life.22

The effects of stopping vary depending on the cancer. For example, ten years after stopping, a person’s risk of lung cancer falls to about half that of a smoker 23. And the increased oral and laryngeal cancer risks practically disappear within ten years of stopping 2. But the risks of bladder cancer are still higher than normal 20 years after stopping 15.

Cutting down the number of cigarettes you smoke slightly reduces your risk of lung cancer,24 but you’ll only experience the full health benefits if you stop altogether. One study found that even smokers who halved the number of cigarettes they smoked had similar risks of dying from heart disease and only slightly lower risks of dying from cancer.25

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Cigarette smoke contains dozens of cancer-causing substances

To date, scientists have found about 70 different cancer causing substances in tobacco smoke 2,26, including arsenic, benzene, formaldehyde and cadmium. It also contains radioactive particles of polonium-210, which become concentrated in hotspots in the lungs, and deliver high levels of damaging radiation.

Several studies have found links between chemicals in cigarette smoke and cancer, by looking for the footprints that these chemicals leave on our genes 27. For example, one study showed that benzo[a]pyrene, a chemical in cigarette tar, damages a key gene called p53. And the researchers found that p53 in lung cancer patients was damaged in exactly the same way as in their experiments 28.

Our Smoke is Poison website has more about these chemicals, their levels in cigarette smoke, what they do in the body and why they’re more dangerous in combination.

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‘Low-tar’ cigarettes are just as bad for you as normal brands

Low tar cigarettes, previously known as ‘light’ or ‘mild’, have similar levels of tar and nicotine to normal brands 29. The main difference lies in the filters. These have large ventilation holes to allow fresh air to mix with the smoke. Fresh air can make up about 70% of each puff 29.

Although official cigarette testing machines register lower tar and nicotine levels, these do not correspond with the levels that human smokers actually inhale 29. Researchers have found that people who smoked low-tar brands smoked harder and more frequently to satisfy their nicotine cravings 30-32.

According to one study, low-tar smokers ended up inhaling about 80% more smoke, and had similar levels of cancer-causing chemicals in their blood 33. They can also inhale over twice as much tar and nicotine as smokers of normal brands 34.

Smokers inadvertently use other methods to get a bigger nicotine fix from low-tar cigarettes, such as blocking the filters with fingers or saliva. One Canadian study showed that over half of discarded cigarette butts showed blocked filters 35.

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Alcohol and other substances worsen the effect of smoking

Tobacco, as well as alcohol, can cause mouth, oesophageal and liver cancers. Scientists have also found that together, their effects are much worse 36-38. And while alcohol does not cause stomach cancer, it can worsen the risk of this disease in smokers.39

One study found that together, smoking and drinking increased liver cancer risk by ten times 36. And a Spanish team found that people who smoke and drink heavily could increase their risk of oesophageal cancer by up to 50 times.38,40 This problem is made even worse because heavy drinkers and smokers often have poor diets 41.

Smoking also interacts with many other cancer risk factors and worsens their effects. For example the lung cancer risk due to exposure to high levels of radon gas is 25 times higher in smokers than in non-smokers 42.

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Second-hand smoking also causes cancer and kills thousands of people every year

Several studies have shown that breathing in other people’s smoke causes cancer in non-smokers 2,43. Second-hand smoke contains several cancer causing chemicals. Many of these chemicals are present in higher concentrations than in the smoke inhaled by the smoker themselves 2.

Studies have consistently found that non-smoking spouses of people who smoke at home have 20-30% higher risks of lung cancer.44 And a review of 22 studies found that people exposed to second-hand smoke in the workplace have 24% higher risks of lung cancer. Those who were exposed to the highest levels of second-hand smoke at work had twice the risks of lung cancer.45

One study estimates that passive smoking may kill over 11,000 people every year in the UK from cancer, heart disease, strokes and other diseases46.

Second-hand smoking also causes other health problems in non-smokers including asthma and heart disease. One study showed that even 30 minutes of exposure to second-hand smoke can reduce blood flow in a non-smoker’s heart 47.

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Children are especially at risk from second-hand smoking.

Children are particularly at risk because they breathe faster than adults and have underdeveloped immune systems. A study by the Royal College of Physicians showed that about 17,000 children in the UK are admitted to hospital every year because of illnesses caused by second-hand smoke 48.

A large study of over 300,000 people found that children who were frequently exposed to cigarette smoke at home had a higher risks of lung cancer as adults 49. Another study found that children in households where both parents smoke have a 72% higher risk of respiratory diseases. And the EPIC study found that exposing children to second-hand smoke increases the risk of bladder cancer later on in life by a third.50

Childhood exposure to second-hand smoke had also been linked to a wide range of other conditions including asthma, Sudden Infant Death Syndrome (or cot death) 51, childhood meningitis 52, mental disabilities 53 and autism 54.

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Smoking while pregnant can harm your baby

Smoking during pregnancy hinders the blood flow to the placenta, which reduces the amount of nutrients that reach the baby 55. Because of this, women who smoke while pregnant have lighter babies than those who don’t smoke 56. And low birth weight can lead to higher risks of diseases and death in infancy and early childhood.

There is also evidence that women exposed to second-hand smoke during pregnancy also have lighter babies 57.

Smoking during pregnancy has also been linked to other pregnancy complications including miscarriage, stillbirth, ectopic pregnancy and cot death. It may also have consequences for the physical and mental development of the child 58.

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Smokeless tobacco can also cause cancer

Smokeless tobacco, also known as chewing tobacco or snuff, is popular in South Asian communities in the UK. Many studies have shown that smokeless tobacco can cause oral cancer, and may cause pancreatic cancer 59,60. One study found that people who used smokeless tobacco had almost 50 times higher oral cancer risks than those who didn’t 61.

The most dangerous chemicals in smokeless tobacco are called tobacco-specific nitrosamines (TSNAs). One review found that people who use smokeless tobacco expose themselves to up to a thousand times more TSNAs than non-smokers, and up to 50 times more than smokers 62.

Smokeless tobacco is also as addictive as cigarettes. Some studies found that the amount of nicotine absorbed from smokeless tobacco is 3-4 times greater than that deliver by a cigarette 63. The nicotine is also absorbed more slowly and stays in the bloodstream for a longer time.

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References

1. Doll, R. and R. Peto, Epidemiology of Cancer. Oxford Textbook of Medicine, ed. D. Warrell, et al. 2003, Oxford: OUP.
2. IARC, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Tobacco smoke and involuntary smoking. Vol. 83. 2004, Lyon: IARCPress.
3. Sasco, A., M. Secretan, and K. Straif, Tobacco smoking and cancer: a brief review of the epidemiological evidence. Lung Cancer, 2004. 45: p. S3-S9.PubMed
4. Peto, R., A. Lopez, and J. Boreham, Mortality from smoking in developed countries, 1950-2000. 2nd ed. 2005, Oxford: Oxford University Press.
5. Vollset, S.E., A. Tverdal, and H.K. Gjessing, Smoking and deaths between 40 and 70 years of age in women and men. Ann Intern Med, 2006. 144(6): p. 381-9.PubMed
6. Doll, R., Mortality in relation to smoking: 40 years' observation on male British doctors. BMJ, 1994. 309: p. 901-911.PubMed
7. Peto, R., et al., Mortality from smoking in developed countries 1950-2000: Indirect estimates from National Vital Statistics. 1994, Oxford: OUP.
8. CancerStats. Lung Cancer and Smoking - UK. 2004 Link
9. Doll, R. and A. Hill, Smoking and carcinoma of the lung; preliminary report. Br Med J, 1950. 2: p. 739-48.PubMed
10. Doll, R., et al., Mortality in relation to smoking: 50 years' observations on male British doctors. BMJ, 2004. 328: p. 1519.PubMed
11. Doll, R. and R. Peto, Cigarette smoking and bronchial carcinoma: dose and time relationships among regular smokers and lifelong non-smokers. J Epidemiol Community Health, 1978. 32: p. 303-13.PubMed
12. Bjartveit, K. and A. Tverdal, Health consequences of smoking 1-4 cigarettes per day. Tob Control, 2005. 14(5): p. 315-20.PubMed
13. Bjerregaard, B.K., et al., The effect of occasional smoking on smoking-related cancers: In the European Prospective Investigation into Cancer and Nutrition (EPIC). Cancer Causes Control, 2006. 17(10): p. 1305-1309.PubMed
14. Wiencke, J., et al., Early age at smoking initiation and tobacco carcinogen DNA damage in the lung. J Natl Cancer Inst, 1999. 91: p. 614-9.PubMed
15. Brennan, P., et al., Cigarette smoking and bladder cancer in men: a pooled analysis of 11 case-control studies. Int J Cancer, 2000. 86: p. 289-94.PubMed
16. McLaughlin, J., et al., International renal-cell cancer study. I. Tobacco use. Int J Cancer, 1995. 60: p. 194-8.PubMed
17. Johnson, N., Tobacco use and oral cancer: a global perspective. J Dent Educ, 2001. 65: p. 328-39.PubMed
18. Johnson, K.C., Accumulating evidence on passive and active smoking and breast cancer risk. Int J Cancer, 2005.PubMed
19. Lim, U., et al., Alcohol, Smoking, and Body Size in Relation to Incident Hodgkin's and Non-Hodgkin's Lymphoma Risk. Am J Epidemiol, 2007.PubMed
20. Luchtenborg, M., et al., Smoking and colorectal cancer: different effects by type of cigarettes? Cancer Epidemiol Biomarkers Prev, 2007. 16(7): p. 1341-7.PubMed
21. Ha, M., et al., Smoking Cigarettes before First Childbirth and Risk of Breast Cancer. Am J Epidemiol, 2007.PubMed
22. Wakai, K., et al., Decrease in risk of lung cancer death in Japanese men after smoking cessation by age at quitting: Pooled analysis of three large-scale cohort studies. Cancer Sci, 2007. 98(4): p. 584-589.PubMed
23. US DHHS. The Health Benefits of Smoking Cessation: A report of the Surgeon General. 1990 Link
24. Godtfredsen, N.S., E. Prescott, and M. Osler, Effect of smoking reduction on lung cancer risk. Jama, 2005. 294(12): p. 1505-10.PubMed
25. Tverdal, A. and K. Bjartveit, Health consequences of reduced daily cigarette consumption. Tob Control, 2006. 15: p. 472-480.PubMed
26. Hoffman, D. and I. Hoffman, The changing cigarette: Chemical studies and bioassays., in Risks Associated with Smoking Cigarettes with Low Machine-Measured Yields of Tar and Nicotine (Smoking and Tobacco Control Monograph No. 13). 2001, NCI: Bethseda. p. 159-191.Link
27. Pfeifer, G., et al., Tobacco smoke carcinogens, DNA damage and p53 mutations in smoking-associated cancers. Oncogene, 2002. 21: p. 7435-51.PubMed
28. Denissenko, M., et al., Preferential formation of benzo[a]pyrene adducts at lung cancer mutational hotspots in P53. Science, 1996. 274: p. 430-2.PubMed
29. Jarvis, M. and C. Bates. Why low tar cigarettes don't work and how the tobacco industry has fooled the smoking public. 1999 Link
30. Russell, M., et al., Relation of nicotine yield of cigarettes to blood nicotine concentrations in smokers. Br Med J, 1980. 280: p. 972-6.PubMed
31. Benowitz, N., et al., Smokers of low-yield cigarettes do not consume less nicotine. N Engl J Med, 1983. 309: p. 139-42.PubMed
32. Hammond, D., et al., Smoking Topography, Brand Switching, and Nicotine Delivery: Results from an In vivo Study. Cancer Epidemiol Biomarkers Prev, 2005. 14(6): p. 1370-5.PubMed
33. Benowitz, N.L., et al., Carcinogen Exposure during Short-term Switching from Regular to "Light" Cigarettes. Cancer Epidemiol Biomarkers Prev, 2005. 14(6): p. 1376-83.PubMed
34. Djordjevic, M., S. Stellman, and E. Zang, Doses of nicotine and lung carcinogens delivered to cigarette smokers. J Natl Cancer Inst, 2000. 92: p. 106-11.PubMed
35. Kozlowski, L., M. Pope, and J. Lux, Prevalence of the misuse of ultra-low-tar cigarettes by blocking filter vents. Am J Public Health, 1988. 78: p. 694-5.PubMed
36. Kuper, H., et al., Tobacco smoking, alcohol consumption and their interaction in the causation of hepatocellular carcinoma. Int J Cancer, 2000. 85: p. 498-502.PubMed
37. Boyle, P., et al., European Code Against Cancer and scientific justification: third version (2003). Ann Oncol, 2003. 14(7): p. 973-1005.PubMed
38. Castellsague, X., et al., Independent and joint effects of tobacco smoking and alcohol drinking on the risk of esophageal cancer in men and women. Int J Cancer, 1999. 82: p. 657-64.PubMed
39. Sjodahl, K., et al., Smoking and alcohol drinking in relation to risk of gastric cancer: A population-based, prospective cohort study. Int J Cancer, 2006.PubMed
40. Boeing, H., Alcohol and risk of cancer of the upper gastrointestinal tract: first analysis of the EPIC data. IARC Sci Publ, 2002. 156: p. 151-4.PubMed
41. Key, T., et al., The effect of diet on risk of cancer. Lancet, 2002. 360: p. 861-868.PubMed
42. Darby, S., et al., Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies. BMJ, 2004. Epub ahead of print.PubMed
43. Department of Health, Secondhand smoke: Review of evidence since 1998. Scientific Committee on Tobacco and Health. 2004.PubMed
44. Taylor, R., F. Najafi, and A. Dobson, Meta-analysis of studies of passive smoking and lung cancer: effects of study type and continent. Int J Epidemiol, 2007.PubMed
45. Stayner, L., et al., Lung Cancer Risk and Workplace Exposure to Environmental Tobacco Smoke. Am J Public Health, 2007.PubMed
46. Jamrozik, K., Estimate of deaths attributable to passive smoking among UK adults: database analysis. BMJ, 2005. Epub ahead of print.PubMed
47. Otsuka, R., et al., Acute effects of passive smoking on the coronary circulation in healthy young adults. JAMA, 2001. 286: p. 436-41.PubMed
48. Royal College of Physicians, Smoking and the Young. 1992.
49. Vineis, P., et al., Environmental tobacco smoke and risk of respiratory cancer and chronic obstructive pulmonary disease in former smokers and never smokers in the EPIC prospective study. BMJ, 2005. Epub ahead of print.PubMed
50. Bjerregaard, B.K., et al., Tobacco smoke and bladder cancer-in the European prospective investigation into cancer and nutrition. Int J Cancer, 2006.PubMed
51. Anderson, M., D. Johnson, and H. Batal, Sudden Infant Death Syndrome and prenatal maternal smoking: rising attributed risk in the Back to Sleep era. BMC Med, 2005. 3: p. 4.PubMed
52. Kriz, P., M. Bobak, and B. Kriz, Parental smoking, socio-economic factors, and risk of invasive meningococcal disease in children: a population based case-control study. Arch Dis Child, 2000. 83: p. 117-21.PubMed
53. Yolton, K., et al., Exposure to environmental tobacco smoke and cognitive abilities among U.S. children and adolescents. Environ Health Perspect, 2005. 113: p. 98-103.PubMed
54. Hultman, C., P. Sparen, and S. Cnattingius, Perinatal risk factors for infantile autism. Epidemiology, 2002. 13: p. 417-423.PubMed
55. Larsen, L., H. Clausen, and L. Jonsson, Stereologic examination of placentas from mothers who smoke during pregnancy. Am J Obstet Gynecol, 2002. 186: p. 531-7.PubMed
56. Misra, D., N. Astone, and C. Lynch, Maternal smoking and birth weight: interaction with parity and mother's own in utero exposure to smoking. Epidemiology, 2005. 16: p. 288-93.PubMed
57. Luciano, A., et al., The influence of maternal passive and light active smoking on intrauterine growth and body composition of the newborn. Eur J Clin Nutr, 1998. 52: p. 760-3.PubMed
58. Cnattingius, S., The epidemiology of smoking during pregnancy: smoking prevalence, maternal characteristics, and pregnancy outcomes. Nicotine Tob Res, 2004. 6(Suppl 2): p. S125-40.PubMed
59. Cogliano, V., et al., Smokeless tobacco and tobacco-related nitrosamines. Lancet Oncol, 2004. 5: p. 708.PubMed
60. Critchley, J. and B. Unal, Health effects associated with smokeless tobacco: a systematic review. Thorax, 2003. 58: p. 435-43.PubMed
61. Winn, D.M., et al., Snuff dipping and oral cancer among women in the southern United States. N Engl J Med, 1981. 304(13): p. 745-9.PubMed
62. Brunnemann, K. and D. Hoffman, Chemical composition of smokeless tobacco products. NCI Smoking and Tobacco Control Monograph, 1993. 2: p. 96-108.PubMed
63. Benowitz, N., Pharmacology of smokeless tobacco use: nicotine addiction and nicotine-related health consequences. NCI Smoking and Tobacco Control Monograph, 1993. 2: p. 219-228.PubMed