By Steve Cross
5th January 2007
‘80% of lung cancers are caused by smoking’
A quick internet search on terms similar to the title of this article will reveal hundreds of medical, health and anti-smoking websites that make this claim. Where do these high numbers and claims of causation come from and how do they fit in with all the other known risk factors of lung cancer?
How does the history of lung cancer fit in with the myth?
Prior to the 1930’s lung cancer had been considered as an extremely rare disease. 1, 2 In fact the university of Minnesota recorded only 4 cases of lung cancer between 1900 and 1920 and the University of Dresden reported in 1878 that malignant tumours of the lung only accounted for 1% of all cancers 3. Smoking on the other hand had been widespread and prevalent for over 300 years prior to this; in fact in 1665 smoking was positively encouraged as it was thought to provide a protective effect from the great plague and the American Revolution in the 16th century was funded primarily from British tobacco taxes.
In the knowledge of this, how can smoking possibly be the major cause of lung cancer? The anti-smoking movement has claimed that it’s because it is only mass machine produced cigarettes that cause lung cancer and these weren’t introduced until 1880. 2
‘While tobacco had been widely used throughout the world for centuries, the present pandemic of lung cancer followed the introduction of manufactured cigarettes with addictive properties, which resulted in a new pattern of sustained exposure of the lung to inhaled carcinogens.’ 4
If there is any truth in this claim it would mean that tobacco is not a risk for lung cancer but only the production methods and it still wouldn’t explain the 50 year gap between 1880 and the 1930’s epidemic of lung cancer. They have also claimed that modern ‘farming’ fertilizers and additives to tobacco have lead to it causing lung cancer. Again; if this is true then it is not the tobacco and these methods are not limited to tobacco production, the same fertilizers are used on food and additives such as the highly carcinogenetic sodium nitrate are routinely added to food to give it a longer ‘shelf life’. Shouldn’t the fight therefore be against fertilizers and additives?
Mankind has actually been inhaling smoke in confined spaces for at least 50 000 years; log fires produce the same chemicals as found in tobacco smoke (the only chemical unique to tobacco is nicotine which is not carcinogenic). It is hard to explain why lung cancer didn’t become a major health problem until the 1930’s, unless you look at risks other than smoke. Can it just be coincidence that the rise of lung cancer coincides perfectly with the industrial revolution?
So where did these high figures of causation actually come from?
The root of the claim can be traced back to a study published in 1954 by Richard Doll and Austin Bradford Hill 5. This study, conducted by post, of 40 000 doctors over a period of 3 years found that 789 of the doctors died during this 3 years and that 36 of them had died from lung cancer. Although this study showed that those doctors who were non-smokers were actually more likely to get lung cancer it also showed that smokers who quit smoking were less likely to get it. Doll concluded from this that the vast majority of lung cancers must be caused by smoking and despite never having researched other possible factors he claimed that environmental and industrial pollution did not cause lung cancer; he even claimed that ‘Agent Orange’, a chemical agent used in the Vietnam war, did not cause cancer. Doll was discredited in 2006 after it was disclosed that he was paid thousands of dollars a day by the manufacturers of the chemicals he claimed to be safe by putting all of the blame onto smoke. 6
As a result of the 1954 study the anti-smoking movement hailed Doll as a hero and despite early criticism of it the message was carried forward. Many smoking studies carried out since include statements in the first paragraph such as; ‘It is well known that smoking is the major cause of lung cancer’. For many years after this study little research was carried out into the effects of environmental pollution due to Doll’s conclusions.
In 1999 a letter from the UK Ministry of Health stated that, based on Doll’s 1981 report, ‘relatively little of the cancer burden (5-10%) is attributed to occupational, environmental or consumer exposure to specific chemicals’.
The chemicals in tobacco smoke are all present in the environment in greater quantities from other sources so how can it be possible that they are harmful only when produced by smoking? It is of little surprise that Doll finally admitted that ‘It does look as if it’s the cancers that are principally caused by hormones that are not affected by smoking. Most of the other cancers throughout the body are induced by exposure to chemicals, often environmental ones’. 7
Recently there has been a shift back towards the pre 1950’s views; Toxicologist Professor Simon Wolff stated; ‘There is no doubt that cigarette smoking causes lung cancer, but there is also no doubt that air pollution, particularly from diesel, is a contributory factor, so important that perhaps without air pollution we would see a much lower rate of lung cancer than we have. For example, in rural China, where people tend to smoke very heavily and where air pollution is much less, the differences in lung cancer rates between smokers and non-smokers is very small, and lung cancer rates are about one tenth of the lung cancer rates in industrialised countries.’
In addition some studies performed after Doll’s claims noted that a high percentage of lung cancer patients were smokers or former smokers; the anti-smoking movement has made much of this in its ‘Smoking Causes’ claims. This basis for conclusion is completely meaningless; a high percentage of people without lung cancer are also smokers or former smokers!
If 70% of the population are drinkers or former drinkers of coffee and 75% of people who can’t sleep are drinkers or former drinkers of coffee, it does not follow that 75% of sleep disorders are caused by coffee. It actually only shows that up to 5% may have something to do with coffee; but even then that can only be claimed once all other possible causes have been eliminated.
There are many other possible causes of lung cancer and many studies have shown that people who live unhealthy lifestyles put themselves at risk of all kinds of disease; people with unhealthy lifestyles also happen to contain the biggest group of smokers.
‘Socio-economic status is associated with a constellation of the following interacting determinants of lung cancer risk: smoking; diet; and exposures to inhaled agents in the workplace and general environment. Lower socioeconomic status is associated with an unfavourable profile for all of these factors.’ 8
‘For both sexes we observed significantly increased consumption of fruits and higher vitamin A and fibre scores in non-smokers compared to current smokers.’ 9
‘People who eat more vegetables are at lower risk of lung cancer than persons who consume fewer vegetables. So non-smokers are at less risk of lung cancer because of their difference in diet.’ 10
Basically smokers are more likely to work in dusty environments, have a poor diet, live in poor quality housing and not take regular aerobic exercise, all of which are shown to be high risk factors for lung cancer 11. They are obviously therefore more likely to contract disease because of these factors and this is not taken into consideration in the anti-smoking claims.
What are the other risk factors for lung cancer and what have the limited studies on them shown?
There are many known risk factors for lung cancer; unfortunately because of Doll’s claims the amount of lung cancers that a particular ‘cause’ is responsible for has not been widely studied. There is however sufficient evidence from reliable sources and epidemiological research that over 50% of lung cancers can be accounted for by risks other than tobacco smoke and that this may well be a conservative figure. See The Causes Of Lung Cancer for a detailed breakdown of the causes of lung cancer and how much each is responsible for.
This revelation alone would appear to be sufficient to state that smoking cannot possibly be responsible for 80% of lung cancers; no-one can argue with the fact that over 130% of people can’t be dying of something. The anti-smoking movement have however attempted to explain this obvious problem of fundamental mathematics by claiming that although risks such as diet and exercise can make a big difference it is still ultimately smoke that gets you. This is yet another unsubstantiated and factually incorrect claim; the studies that have been used to calculate the risk factors all took smoking out of the equation. If 20 to 42% of lung cancers in never smokers are due to poor diet then an even higher percentage of lung cancers in smokers are also due to poor diet. (An even higher percentage because, as has already been disclosed, smokers in general have poorer diets.)
How do worldwide trends in lung cancer compare to trends in smoking?
Again the discredited ‘godfather of the anti-smoking movement’, Richard Doll was the man who first made the claim that lung cancer trends follow smoking trends. He made these claims from a research he published in the 1990’s where he showed that lung cancers in men in the UK began to fall in the 1970’s roughly 20 years after smoking began to decline. Virtually all anti-smoking and health related web sites and literature refer to and quote this research as the evidence that lung cancers are almost exclusively caused by smoke. There is however considerable evidence that this is not the case;
Firstly, the calculations of Doll’s study were once again called into question as they disagreed with all of the available figures of the time;
‘Professor Doll’s and Professor Peto’s statistics go against the commonly held assumption that the UK trails much of Europe and the US in cancer treatment.’ 12
Apart from the highly dubious source of the claims, trends from virtually everywhere else in the world simply don’t agree that there is a high correlation between declines in smoking and declines in lung cancer.
A look at some figures from around the world;
|Prevalence of smokers compared to prevalence of lung cancers: US trend 1955 to 1990 Males.|
|year||% smokers||lung cancer/100 000|
As can be seen in this chart lung cancers in American males continued to rise for 35 years after declines in smoking began; if there is any truth that almost all lung cancers are caused by smoking then these figures would show that American male smokers don’t get lung cancer until at least 35 years after they quit.
That could be the only reason that they were still rising 35 years later and a 35 year latency argument is not particularly compelling when you consider that some of these people would have been smoking for 40 years or more before they quit; that would mean they didn’t get lung cancer until up to 75 years after they started smoking and if that were true there seems little point in worrying about it.
|Prevalence of smokers compared to prevalence of lung cancers: US trend 1944 to 1990: Females|
|year||% smokers||lung cancer/100 000|
The chart for female Americans also shows absolutely no correlation between lung cancer and smoking. Female smoking prevalence peaked during the war and for 35 years remained fairly constant with small increases and decreases through those decades before a big drop by 1990 yet lung cancer rates have increased by 775%. How can smoking be strongly related to lung cancer when over a 45 year period smoking prevalence fell by 42% and lung cancer increased by 775%?
These figures are made worse by the fact that lung cancer in American females has still not peaked while smoking rates have continued to fall. The only thing that these charts actually do correlate with is regulatory measures on industry such as the 1970 Environmental Protection Agency, Clean Air Act. 15 Measures such as these to cut industrial air pollution fit well with the start of reductions in lung cancer in men showing a much more plausible 15 to 20 year latency during implementation and the gradual reductions in air pollution over that period. The large increases in female lung cancer cannot in any way be associated with smoking but it may however be explained by an ever increasing number of women entering the industrial workplace since the war.
|Prevalence of smokers compared to prevalence of lung cancers: Japan trend 1958 to 1990 Males|
|year||% smokers||lung cancer/100 000|
The data from Japan shows once again that despite falls in smoking prevalence over decades, lung cancer rose. Another interesting aspect of this data is that after WW2 Japans male smoking rate was similar to the UK; by 1990 however the UK smoking rate had dropped to around 30%, half of Japans rate. Yet lung cancer in UK males was double that of Japan in 1990. Once again, how can smoking be the cause of virtually all lung cancers if Japan has double the amount of smokers and half the amount of lung cancers compared to the UK?
It is not only the US and Japan that shows these results, some of the latest figures on smoking prevalence and lung cancer from around the world indicate that the largest smoking nations do not have lung cancer as high as the UK and the US;
|Prevalence of smokers compared to prevalence of lung cancers: Males 1990 to 1999|
|Country||% smokers||lung cancer/100 000|
From the above table it is easy to see that the nations with the highest smoking levels don’t have lung cancer rates anywhere near as high as the UK and the U.S. The excuse often given for this is that these nations haven’t been ‘big’ smokers until recently. This however is clearly not true; Smoking trends in Japan for example as we have already shown were as high in Japan just after WW2 as they were in the UK. In Taiwan male smoking rates have been between 60 and 80% since at least 1970 19and there are serious discrepancies between tobacco usage and lung cancers in women;
‘Although cigarette smoking is considered to be the most important cause of lung cancer, smoking behaviour cannot fully explain the epidemiological characteristics of lung cancer in Taiwanese women, who like Chinese women in the U.S, Hong Kong, Singapore, Malaysia and some cities in mainland China smoke relatively rarely but contract lung cancer relatively often’ ..’In Taiwan only 10% of smokers in female lung cancer patients was observed’ 20
In addition to the above; other European countries such as Spain, Greece and France have similar lung cancer rates to the UK despite having double the smoking levels. In fact there is a general trend around the world that the more industrialised areas such as France, Spain, Italy, Hong Kong, Canada, USA and the UK have more lung cancer; In addition poor and heavily industrialised nations such as Hungary and Poland have the worst lung cancer rates of all. This can be contrasted with less heavily industrialised nations such as Sweden, Denmark, China and Norway which all have much lower lung cancer rates. 17
The rise of lung cancer coincides perfectly with the industrial revolution and lung cancer was extremely rare prior to the 1930’s despite smoke inhalation being widespread for thousands of years.
The other risk factors for lung cancer quickly add up to more than the 20% available for causes of lung cancer if the claim of 80% is believed; these other risk factors include, but are not limited to; diesel, radon, plutonium, asbestos, industrial waste, industrial pollution, workplace ‘dust’, other vehicle emissions, perfumes and make-up, pets, diet, cooking fumes, natural gas, other forms of radiation, infection, genetics, cleaning agents, diet, physical inactivity, bacteria and viruses.
The claims originally arose from flawed data presented by a discredited researcher and the claims were not supported by the results of his study. Nowadays any statistician who can show a link between smoke and disease is rewarded with huge funding grants from health departments, the anti-smoking industry and producers of nicotine replacement therapy.
Trends from around the world do not support the hypothesis that smoking is such a high cause of lung cancer.
This myth is busted.
1. Primary malignant neoplasms of the lung are among the rarest forms of disease : Primary Malignancies, I. Adler, 1912
5. Bradford Hill A, Doll R. The Mortality of doctors in relation to their smoking habits. A preliminary report. BMJ 1954
12. The Guardian
13. Chest Journal