Select Committee on Economic Affairs Minutes of Evidence

Examination of Witness (Questions 381-399)

Professor Sir Richard Peto

14 FEBRUARY 2006

  Chairman: Thank you very much for coming. You know the routine pretty well, I guess, and your expertise is going to be, I am sure, very helpful to us in our study of these questions of risk. I am told to remind everybody who comes to be a witness to speak up and to speak slowly and clearly so that we get an accurate report of what you have to say. You know something of the questions, but if I may I will ask Lord Macdonald if he would like to start.

  Q381  Lord Macdonald of Tradeston: Sir Richard, I wanted to start by asking if you could give us your assessment of the health risks associated with passive smoking in the home or at work and in other public places. It would be helpful if you could give us an indication of both absolute and relative magnitudes of the health risks and also the degree of uncertainty attached to the available statistical evidence.

  Professor Sir Richard Peto: I am sorry, I know that is what you would like to be given, but the point is that these risks are small and difficult to measure directly. What is clear is that cigarette smoke itself is far and away the most important cause of human cancer in the world—that is, cigarette smoke taken in by the smoker—and passive smoking, exposure to other people's smoke, must cause some risk of death from the same diseases. Measuring that risk reliably and directly is difficult. You can do it indirectly by suggesting approximate proportionality of hazard to exposure, but the assumptions become almost untestable. The arguments that have been forward for the various thresholds, that there is some dose below which there is absolutely no risk, have no scientific plausibility. They have come up a lot of times because, as you know, when there is the statement "there is some risk" then there is political pressure to get rid of that risk, so it would be very convenient if one could be told that there was no risk, and so various implausible models involving thresholds got proposed. There is going to be some risk and there is always going to be quite a lot of uncertainty about the magnitude of that risk, I am sorry. What is definite is that cigarette smoke is causing about 100,000 deaths a year in this country, and a few million deaths a year worldwide, that this number of deaths is still increasing in some other countries, although not in this country, and that passive exposure to cigarette smoke in various circumstances must be producing some risk. That is definite, and the threshold arguments are often politically motivated inventions which do not have much scientific plausibility. I am sorry not to be more helpful; you want numbers and I could give you numbers by direct extrapolation, but what does one make of them? These hazards cannot be directly measured.

  Q382  Lord Macdonald of Tradeston: If you have such a large sample of people dying of lung cancer, would it be possible to interview them about their personal circumstances in a way that would allow you to deduce whether they had frequented bars or had a smoky home or whatever?

  Professor Sir Richard Peto: This has been done. People who persistently smoke cigarettes have about 20 times the lung cancer risk of those who never smoke; that is a 2000 per cent excess. The exposure that one would get when breathing other people's smoke obviously depends on the circumstances, but even heavy exposure would be something like one per cent of what a smoker gets, maybe in other circumstances 0.1 per cent, so you would expect if there was proportionality to get something up to about a 20 per cent excess. That is what you see in the average of all the studies, and people have pointed to the uncertainties in this evidence—it could under-estimate the real hazards, or it could over-estimate the real hazards. It is however, roughly what you would expect from simple proportionality.

  Q383  Lord Skidelsky: 2000 as opposed to 20.

  Professor Sir Richard Peto: Yes. You would expect an excess of a few per cent, or several per cent. The one thing that is often left out of this is that these are the excesses for lifelong non-smokers. Smokers who have stopped, who have given up smoking, have much less lung cancer risk next year than they would have had if they had not stopped, but they still have a lot more risk of lung cancer than if they had never smoked. A lot of the cells in their lungs will be altered part-way towards cancer for the rest of their life, and if they are lucky then they will live out the rest of their life and none of those cells will suffer that final step. Those people would probably be at greater risk of damage from breathing other people's smoke than lifelong non-smokers would be, because lifelong non-smokers are going to have so few cells that are at risk of that final step. But, of course, when studying people who have smoked for 10 years or 20 years and then stopped, it is very difficult to work out exactly what their risk would be without passive smoking, so it is difficult to do reliable epidemiological studies of them. So, people have done epidemiological studies of lifelong non-smokers because it is a cleaner comparison. It is however, the ex-smokers, those who have stopped, who are probably going to suffer the greatest absolute risk as a result of exposure to other people's smoke, at least in terms of cancer.

  Q384  Lord Macdonald of Tradeston: I am just trying to see if you can break it down into categories. Presumably, non-smoking shepherds would be much healthier than non-smoking traffic wardens.

  Professor Sir Richard Peto: There probably would not be a very big difference. The amount of exposure from cigarette smoke is so much greater than the amount that you would get from the ambient air outside in the city, certainly nowadays, that there is not so much difference between non-smokers in urban and rural populations. There are some differences, but they are really quite small.

  Q385  Lord Macdonald of Tradeston: What I was heading towards is the suspicion that the next way this is taking us might be the banning of smoking in the home, and I wondered what evidence you would bring forward that would allow that debate to take some sensible form.

  Professor Sir Richard Peto: I do not want to be cast in the role of advocating banning smoking in public places or in private places. What I am concerned with is that enormous risks should be taken seriously, like the extent to which smokers kill themselves—there is about a 50 per cent chance that a person who smokes cigarettes and continues to do so will be killed by tobacco, which is vastly greater than almost any other risks around. It is the relative importance of this that I somehow want to get across. But, we are concentrating now, because this is your task, on the effects of breathing other people's smoke, although the main way smokers kill people is by killing themselves, not by killing other people—they are a lot better at killing themselves than they are at killing other people.

  Q386  Chairman: It is very difficult, but the message I am getting is that when you look at the evidence that is put forward by the tobacco companies to say there is not any serious evidence, or when you get evidence put forward by people who are totally opposed to smoking of any sort, then when you come to deal with the question of passive smoking you would be sceptical about any of the evidence that is produced on either side, further than you have indicated.

  Professor Sir Richard Peto: I think there has got to be some risk. The extent to which active smoking is causing cancer, heart disease and lung cancer is enormous. There is about a 50 per cent chance that a smoker who carries on smoking will eventually be killed by this, and that is definite. When you place the same mix of chemicals, more or less, in to the general air, it must cause some risks, so I think the statement that there is some risk to non-smokers is well-founded; you would have to use the most extraordinary, implausible metaphysical arguments to argue for threshold doses below which there is zero risk, especially in a world where there are a lot of ex-smokers whose lungs are already well off any zero on the dose response relationship. The definite statement is that some people are killed by breathing other people's smoke, and then there is reasonable uncertainty about the number killed. I am sorry—there is bound to be wide uncertainty when you are trying to measure risks like this. There is, however, a rather odd finding, which seems to come up repeatedly, of quite a marked excess of mortality from heart disease among those exposed to other people's smoke. This is odd because the hazard is much bigger than you would expect from extrapolation from the hazards faced by smokers. It is not impossible, but it is odd, and in the case of heart disease, the apparent risks in passively exposed non-smokers are bigger than one would have expected. It is possible, however, that there are paradoxical dose response relationships, with rather substantial risks at low doses. To take an extreme example, if you plotted the probability of sneezing against the dose of smoke, smokers on the whole do not make themselves sneeze but they can quite easily make non-smokers sneeze. This example shows that there can be a medical effect with a very odd dose response relationship. It is not impossible, therefore, that passive smoking produces a substantial risk of heart disease, and if that were so then it would represent a really substantial public health hazard. There is argument as to whether such a hazard is real, and there is still reasonable disagreement about this, but I do not think there is reasonable disagreement with the statement that smokers do kill some non-smokers.

  Q387  Lord Skidelsky: I just want to ask a supplementary. You would be reluctant then to commit yourself to a statement such as that in first report of the Select Committee on Health: "It is currently estimated that second-hand smoking causes at least 12,000 deaths each year in the United Kingdom . . .", which was repeated by the Secretary of State on the Today programme this morning. The way the legislation and the case are being presented is much more definite than the statement you have just made.

  Professor Sir Richard Peto: Yes. That is the approximate number that you would get if you take the excess of heart disease deaths that is observed among people exposed to other people's smoke. If you take the heart disease risk as real, then you could get estimates like the one you quoted, and there is argument as to whether the heart disease risk is real or not. I do not know, and you have a very difficult job in deciding what rules to enact. I was asked in the papers you sent me whether regulations on passive smoking or breathing other people's smoke should be promulgated because they would reduce the number of people who choose to continue smoking themselves. I do not want to argue for or against any rule, but there does seem to be a consensus that it would affect the number of people who choose to smoke. If that were not the case, then the tobacco industry would not be so concerned about it, and the strength of their concern does indicate that their reckoning is that it would decrease the number of people who continue to smoke. If that is the case then one side-effect of such regulations would be to avoid quite a number of premature deaths, but I do not want to distort the direct science of what breathing other people's smoke does for the non-smoker or, more importantly, the ex-smoker on account of that. If, however, you are making regulations, then probably you should bear in mind both the direct and the indirect effect of those regulations; it would be irresponsible not to do so.

  Q388  Lord Roper: Sir Richard, you have from time to time used the word extrapolation as a way of getting to these sorts of estimates of risk. I think I follow what you mean by that, but I wonder if you could restate what you would be extrapolating from and what the process would be.

  Professor Sir Richard Peto: Extrapolation is the common-sense idea that if you get about one per cent as much exposure then you might get about one per cent as much risk, or something of that order of magnitude. Obviously, the dose response relationship does not have to be a straight line, and to the extent that it is not a straight line then those answers might be wrong, they could be too high or too low.

  Q389  Lord Roper: But numbers like the 12,000 are numbers which have arisen . . .

  Professor Sir Richard Peto: That particular number came from another source. The trouble is that because these risks are small they are difficult to measure, for obvious reasons. In many populations the main way cigarette smoke kills smokers is by causing death from heart disease rather than causing death from lung cancer. Studies have been done, as you suggested, on lung cancer patients, asking what they smoke, how they lived—and those studies indicate in aggregate, roughly the sort of risk that you might expect from extrapolation of the risks among smokers. On heart disease, similar studies indicate risks from passive exposure that are a lot bigger than would be expected from extrapolation downwards from the effects of smoking on the smoker. Nobody has really argued the studies away, yet everybody feels uncomfortable with the conclusion, unless it could be better understood. Another problem in studying heart disease rather than lung cancer is that whereas lung cancer is quite a rare disease in non-smokers, heart disease is quite common and has many different causes. If you just try and compare people getting heart attacks with others, then you do find an excess of people exposed to other people's smoke, but it is very difficult to interpret this reliably. I do not think—and I could go into this if you want—that the suggestion by the tobacco industry that there is no risk is plausible, but there is a wide range of estimates coming from other sources.

  Q390  Lord Sheppard of Didgemere: In addition to the debate that has taken place on passive smoking, there has also been a debate at various times about such things as traffic exhaust. Given that it is difficult to measure the effects of passive smoking impact on non-smokers, it is probably equally difficult to measure the impact of exhaust systems, but do you want to comment on those two debates that have occurred at various times in the last years?

  Professor Sir Richard Peto: In terms of general pollution it has been possible to demonstrate the hazards of persistent exposure to coal smoke, because there have been lots of cases where the hazard has been so extreme that it has been really clearly demonstrable; it is more difficult with traffic exhausts because whole populations in an area of a city are exposed to them and the main concern about traffic exhausts is not that they are going to cause cancer in the non-smoker, but they are going to make the risks bigger in the smoker. That is very difficult to measure because there are variations in the way people smoke and the intensity with which they smoke their cigarettes can also produce differences in risk, so the main concern about traffic exhausts is not whether they kill non-smokers but whether they increase the risk among smokers, as radon has recently been shown to do. Radon as a pollutant of the domestic environment, of houses, increases the extent to which cigarettes kill people, it multiplies up the risks of smoking, and the concern is that some of these other sources of pollution might do the same. In the case of radon, the hazard happened to be measurable because technically it was relatively easy to measure persistent differences in exposure.

  Q391  Lord Sheppard of Didgemere: Going back to passive smoking as such, does it matter if one cannot measure the impact of a regulation? If, for example, the effect is that it stops parents smoking at home in front of their children, it most probably helps, does it?

  Professor Sir Richard Peto: Does it matter if one cannot measure it? I am sorry, I do not quite follow the question.

  Q392  Lord Sheppard of Didgemere: The policy can still be right even if, when you got down to it, one might even be accused of exaggerating the impact of it?

  Professor Sir Richard Peto: The main thing that parents smoking definitely does is that it encourages the kids to smoke. Kids who live with parents who smoke are more likely to smoke themselves and, therefore, are more likely to get killed by smoking; there is an association of the smoking habits of the parents with the smoking habits of the children when the children reach adult life. When considering the hazards for smokers, we now know that cigarette smoke is an extraordinary mix of toxic chemicals and what is really surprising when you look at the pharmacology of cigarette smoke is that half of all smokers do not get killed by it. That is really the surprising thing: there are thousands of chemicals that have been identified in cigarette smoke, you breathe them in and you get an increased risk of cancer of the mouth, throat, oesophagus and lungs; they go to the edge of the lungs and cause emphysema and then they go around the body and you finish up with mutagens damaging all the cells of the body that are exposed to these chemicals. Eventually they get concentrated in the urine, in the bladder, causing a risk of cancer of the bladder, and even after the smoker passes urine the urine is mutagenic to cultured cells in the laboratory. It is really surprising that more than half of all smokers are not killed by their habit. I notice that in their evidence to this committee the tobacco manufacturers described the cellular repair systems trying to repair the damage done by chemicals; it is remarkable how well they work, given this permanently mutagenic fluid in which the smokers' cells live all the time, yet you finish up with only half of the smokers getting killed by it.

  Q393  Lord Macdonald of Tradeston: A quick follow-up on exhaust fumes. About 30 years ago there was public concern about lead in exhaust fumes and action was taken.

  Professor Sir Richard Peto: Yes.

  Q394  Lord Macdonald of Tradeston: Has there subsequently been evidence of reductions in the related illnesses that were causing the concern?

  Professor Sir Richard Peto: I am sorry, I have just got no useful information to answer that. I have read popular articles suggesting that, yes, exposure was reduced—the trouble with current levels of exposure to lead is that we are a lot too close to the levels of lead in the blood that do have measurable effects on human intelligence. We are within a factor or two of levels that would actually have measurable effects. But, although the effects on intelligence of current exposure levels might not be measurable, this is one of the exposures where we do not have any kind of comfortable safety margin. Nobody, if one had a choice based purely on toxicology, would want to be as near as we are to a level of blood exposure that has measurable effects on intelligence.

  Q395  Lord Skidelsky: This is really the follow-up to Lord Sheppard's question: recent research, based on evidence from America, appears to suggest that a ban on smoking in public places might actually increase smoking in the home, which is much the most important source of the danger of passive smoking. Does one then, by passing legislation, run the risk of simply transferring the habit and its effects from a less dangerous place to a more dangerous one?

  Professor Sir Richard Peto: I am sorry, I am much more of a student of the consequences of smoking than of the causes of smoking, and I do not know whether that statement is true or not. This is not an area that I have studied, I am sorry, as to how regulations on smoking in public places would affect the extent to which people smoke at home.

  Q396  Lord Skidelsky: It is a question about consequences rather than causes because legislation may have these unintended consequences.

  Professor Sir Richard Peto: I stand informed. If you say it does then . . .

  Q397  Lord Skidelsky: I am quoting a study. I have a supplementary to that—or would you like to say any more about that?

  Professor Sir Richard Peto: No, not really. The key thing about smoking in the home is (a) the parents, or whoever it is in the home, have a fair chance of killing themselves and (b) they have a fair chance of making it more likely that the kids start to smoke.

  Q398  Lord Skidelsky: The argument is that the effect of passive smoking is much greater in the home than in a more public place because of the proximity of contact between the smoker and the non-smoker, and it is the continuity of contact as well as the proximity.

  Professor Sir Richard Peto: I do not know what effect such legislation would have on where people smoke. One thing is that people addicted to nicotine seem to need is to get their blood levels up to a certain level, and I am not sure that what they have been doing during the day would have very much carry-over effect as to what they were doing in the evening, but I do not know.

  Q399  Lord Skidelsky: Thank you. If I could ask a supplementary, it is really more of a technical one. In the evidence we received from the Imperial Tobacco Company—

  Professor Sir Richard Peto: I was sent a copy of it last week.

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