120
Abortion SIR,-Dr Joyce Poole (May 30, p 1340) is slightly confused in her assertions of the views of the Catholic Church on the status of the human embryo. What the Church has repeatedly said is that from the beginning of the fertilisation process the embryo is new human life, and this fact alone should govern its status, dignity, and rights under the law. Justice requires that an equality of respect be given to all human life and not merely because of its characteristics, attributes, or achievements. Poole feels that to describe the embryo as a person is incorrect because it has not had time to develop at least some of the properties of personhood. The Lockean understanding of personhood1 is that of manifest self consciousness and rationality, abilities that develop gradually and continuously by virtue of the potential capabilities of human embryo from conception onwards. But the Church believes it is wrong not to respect human life before it has attained these further properties. If this moral principle of respect for human life is reduced to the level of a subjective preference it would erode the foundations of British and other systems of justice. The Catholic Church has never pronounced that ensoulment occurs at conception. How could it possibly attain to such certitude? The links between contraception and abortion centre on the fact that many of the methods used in contraceptive techniques are abortifacient and that when failures occur abortion is used to take up the slack from inadequate contraception. When the contraceptive pill is used regularly and correctly failure rates of 05-2-0 pregnancies per 100 women years are reported. Used in the big world, however, away from controlled trials with medical supervision, different figures are cited-ie, failures of 2-16% in the USA and over 20% in developing countries. In developing countries, women who stop the pill within a year have an average conception rate of 55%.2 Population growth cannot solely be regulated by widespread use of contraceptive techniques. The late Christopher Tietze of the Population Council in America stated that "barring a major breakthrough in contraceptive technology or major modifications in human sexual behaviour, levels of fertility required for population stabilisation cannot be easily obtained without induced abortion". Louis Newman of the USA Department of Public Health and a former President of the American Gynecologist’s Association has said that "No country can reduce its population growth significantly without resorting to abortion". The disastrous consequences of arbitrary government interference in India and China are widely known. Poole in her great sympathy for the women of Brazil, which we all share, must surely appreciate that profound cultural factors operate in many of the developing countries that are opposed to contraception. They can only be eliminated by education, which in turn is dependent on economic growth. This is the basis of the pleading by the Catholic Church for a greater balance between the economies of the developed and the developing countries. At the same time the Church recognises the need for efficient natural family planning and has directly sponsored clinics and services to this end in 84 countries. Natural family planning depends on acceptance by the family that birth limitation is necessary. Guild of Catholic Doctors,
Brampton House, Hospital of St John and St Elizabeth,
PETER DOHERTY,
London NW89NH. UK
Editor, Catholic Medical Quarterly
1. Lock
J. Identity and diversity: essay concerning human understanding (1694). Reprinted in: Perry J, ed. Los Angeles. University of California Press, 1975: 33-52. 2. Moreno L, Goldman M. Contraceptive failure rates in developing countries. Int Fam Planning Perspec 1991; 17: 44-49.
SiR,—Iwould comment on some of Dr Ryder and Mr Justice’s points (June 20, p 1544) about my report (May 30, p 1340). I am aware that the Church condones so-called natural family planning, though only since 1950; before this, "periodic abstinence" was firmly condemned as frustrating the basic procreative purpose of marriage. Unfortunately, the method has been found to be of very limited use in most developing countries. Father Sean McDonagh, writing from his wide experience as a missionary in the Philippines, reports that "not a single family, even those with daily contact with a
clinic sister, was able effectively to apply the method". Nor was he able to find evidence that any country had been able to reduce its population without using artificial methodsIt is well known, of course, that family limitation has been imposed in China just as it was prohibited in Romania, with equally disastrous results, but this is an indictment of totalitarian regimens not contraceptive clinics. With respect to the term unborn child, I suggest that Dr Ryder might look again at Gray’s Anatomy, in which he will find that the term embryo is not used until the structure that is to become the fetus is formed at about the 14th day: "Only the cells where the two vesicles (the amnio-embryonic and the yolk sac) are in contact with each other contribute to the formation of the actual embryo". Development from the time of fertilisation until this point is referred to as the pre-embryonic period for the good reason that until the embryonic area or shield has formed there is in fact no embryo-far less an unborn child. The term pre-embryo, preferred by Warnock for the first 14 days, rests on firm biological ground. Although the Church does not claim that a person is present from fertilisation, it takes the morally safe course followed by Mr Justice, that the conceptus should be regarded as having human status from the moment of conception. Fertilisation is, however, a process, not a moment, and the only incident that could possibly be regarded as momentary is the penetration of the zona pellucida by a single spermatazoon; the subsequent extrusion of the polar body of the ovum and the merging of the pronuclei of the maternal and paternal gametes can take up to 72 h. Until then the fertilised ovum has not yet acquired the human genome and there is evidence that the process of chromosomal pairing may frequently go wrong. Unsuccessful pairing results in a conceptus that is incapable of developing into a human being; a defective maternal pronucleus, for example, may lead to the formation of a hydatidiform mole which, though it results from fertilisation, can in no way be regarded as human tissue. It is thus not selfevident that the cleaving embryo has, or should be deemed to have, a moral status equivalent to that of the human person2 yet it is on this uncertain premise that the Church bases its condemnation of abortion at however early a stage, as well as a whole range of widely used contraceptive methods. The embryo is a dynamic structure of human cells with a wide potential, but at its earliest stages it cannot properly be said to be the individual human being into which it may come to grow any more than the clay on the potter’s wheel is already a particular pot.3 Ednam East Mill,
Kelso,
Roxboroughshire TD5 7QB, UK
JOYCE POOLE
1. McDonagh S. The greening of the church. New York: Geoffrey Chapman, 1990. 2. Dunstan GR. The status of the embryo: perspectives from moral tradition. London: King Edward’s Hospital Fund for London, 1988. 3. Coughlan M. The Vatican, the law and the human embryo. Basingstoke: Macmillan, 1990.
Calcitonin treatment of osteoporosis in Italy SIR,-As President and past President of the Italian Society of Osteoporosis and as researchers for several years in the study of metabolic bone diseases, we would comment on Dr Magrini and colleagues’ report (Feb 22, p 499). We agree with the financial concern that the widespread use of calcitonin in Italy could cause an excessive rise in public health costs because of occasional misprescribing of the drug by physicians. However, Magrini and colleagues’ doubts about some properties of the drug and their statement that there is no evidence that calcitonin is beneficial in elderly patients are unjustified. Calcitonin has a potent inhibitory effect on bone resorption, binding to specific receptors on osteoclasts. It is effective when given parenterally or by the nasal routed Apart from oestrogens, calcitonin is the only pharmaceutical compound approved by the Food and Drug Administration for the treatment of established osteoporosis in the USA. Magrini’s observation that calcitonin prescriptions in Italy exceed those in other European countries is not surprising since the clinical trials on calcitonin conducted in this country were among the first to contribute important scientific evidence on the effects and efficacy of the product.2 Furthermore, it has not been proven
121
that the results of the drug consumption survey done in Emilia Romagna region can be extrapolated to the whole of Italy. With respect to calcitonin in elderly patients, most open or double-blind, controlled, randomised studies that confirm the drug’s effect on bone mass were done in subjects with established osteoporosis, with a mean age of about 65 years and proven vertebral ttacrures.2.3A large case-control study (MEDOS) on the incidence of risk factors for hip fracture was done in 1989 in Portugal, Spain, France, Italy, Greece, and Turkey, with the collaboration of WHO and the European Foundation for Osteoporosis. The results (presented at the llth international conference on calcium regulating hormones in Florence, in April, 1992) demonstrate that calcitonin combined with calcium significantly reduces the risk of hip fracture. Consequently, if the Emilia Romagna analysis, which indicates that calcitonin treatment lasts on average 45 days, were typical of all regions in Italy, then an increase in the duration of treatment could be recommended to further reduce fractures in elderly patients. The analgesic activity of calcitonin is well known.4,5 Finally, it has been proven that calcitonin inhibits oestrogendependent bone loss, both in physiological menopause6,’ and after oophorectomy,8 and provides an important alternative in the prevention of menopause-related bone loss in women who are unable or unwilling to take oestrogens.I Thus published data are certainly not consistent with Magrini and colleagues’ doubts that calcitonin is among the drugs on the Italian market that are devoid of proven clinical efficacy. Internal Medicine II, Medical Clinic, Università degli Studi di Roma "La
Sapienza",
00161, Rome, Italy,
G. F. MAZZUOLI C. GENNARI
and Istituto di Patologia Medica, Università degli Studí di Siena 1. Consensus
Development Conference: prophylaxis Osteoporosis Int 1991; 1: 114-17.
2. Mazzuoli
G, Passeri M, Gennari C,
et
and
treatment
osteoporosis.
al. Effects of salmon calcitonin in
postmenopausal osteoporosis: a controlled double blind clinical study. Calcif Tissue Int 1986; 38: 3-8. 3. Overgaard K, Riis BJ, Christiansen C, et al. Nasal calcitonin for treatment of established osteoporosis. Clin Endocrinol 1989; 30: 435-42. 4. Gennari C, Agnusdei D, Camporeale A. Use of calcitonin in the treatment of bone pain associated with osteoporosis. Calcif Tissue Int 1991; 49: S9-S13. 5. Lyritis GP, Tsakalakos N, Magiasis B, et al. Analgesic effect of salmon calcitonin in osteosporotic vertebral fractures: a double-blind placebo-controlled clinical study. Calcif Tissue Int 1991; 49: 369-72. 6. MacIntyre I, Stevenson JC, Whitehead MI, et al. Calcitonin for prevention of postmenopausal bone loss. Lancet 1988; i: 900-02. 7 Gennari C, Agnusdei D, Montagnani M, et al. An effective regimen of intranasal salmon calcitonin in early postmenopausal bone loss. Calcif Tissue Int 1992; 50: 381-83. 8. Mazzuoli GF, Tabolli S, Bigi F, et al. Effects of salmon calcitonin induced by ovariectomy. Calcif Tissue Int 1990; 47: 209-14.
on
the bone loss
Deaths from tobacco SIR,-Professor Peto and colleagues’ report (May 23, p 1268) provides indirect forecasts of mortality from smoking in the developed countries. Although more narrow in scope and using a different (and what is claimed to be a more robust) methodology than the study by some of the same authors reported at the Perth World Smoking and Health Conference in 1990, this is nevertheless one of the most ambitious exercises in quantitative epidemiology ever to be published. Since these and similar forecasts are likely to determine public policy, it is important that what will be regarded by decision-makers as expert advice is in fact well-founded. Forecasting is a notoriously fragile process and in view of the widespread scepticism about pronouncements in this field,l it is not unreasonable to look very carefully at the provenance of the latest set of forecasts.
Any forecasting procedure should include assumptions about the underlying relations, which are most conveniently considered in terms of a mathematical model. The resulting forecasts will be determined by the content and structure of the underlying model. However, the biological and physical mechanisms that determine death in man are poorly understood, especially with respect to possible agents such as tobacco. All types of smoking-related disease also arise in people who have never been exposed to tobacco smoke, and it is clear that other influences
or
confounding factors may be
involved. Neither the identity nor the relative importance of such factors in relation to any particular cause of death has been established on a definitive basis, although many associations (which may or may not be causal) have been reported. Nor is it known how the confounding factors may combine with any effects of tobacco to produce changes in the health status of the individual. On general grounds, it is very likely that the set of relevant confounding factors will vary from disease to disease as well as from society to society. Potential confounding factors may themselves be associated with smoking habits. For example, in societies where the smoking habit is well-established (which in general are the only societies for which evidence can be obtained), smoking is associated with low social class. The innate characterisics of the individual must also play a part, but the only available quantitative evidence about these matters is derived from uncontrolled epidemiological studies in which smokers and non-smokers are self-selected groups. There is no reason to suppose that the smoking habit is determined independently of personal characteristics or confounding factors. On all these grounds, it is clear that any model that is devised as a basis for generating forecasts on the basis of available knowledge is tentative. None of the models used by Peto and his colleages in recent publications seem to take account of these complex issues, and no evidence is presented that the simple models that are used do provide a realistic representation of the factors involved. Having summarised the experience of a "survey" population in terms of a mathematical model, Peto et al apply the results with the same model to a different target population, often in a different era and possibly in a different part of the world. This implies that the extent of any hazard associated with smoking is exactly the same in both survey and target populations, as are the confounding factors and the associations between the elements of the model. In view of the likely presence of differences in the properties and amounts of tobacco smoked, in the way the tobacco is smoked, in the confounding variables, and in the self-selection criteria for smoking, this is indeed a major act of faith. Peto’s indirect method of forecasting is thus subject to these general criticisms. In addition, the use of lung cancer rates as a yardstick involves further unsupported and arguably implausible hypotheses, including the assumptions: that lung cancer rates in non-smokers as reported in national statistical returns must be the same in the survey and target populations; that any relation between smoking, confounding factors, and mortality are of the same form for all relevant diseases; and that different types of product affect specific diseases in the same way. Furthermore, the arbitrary halving of the calculated excess risk associated with smoking may be generous to the tobacco industry, but does not seem to have any scientific foundation. A detailed analysis of the difficulties of assessing smoking-related mortality is being published elsewhere2 and will not be repeated here. Nevertheless, with the evident uncertainties of this process, it is impossible to avoid the question as to whether the calculation by any method of forecasts of mortality due to smoking on the basis of available information can ever be a proper foundation for public policy or anything more than an exercise in speculative arithmetic. Ide House, Ide, Exeter EX2 9RB, UK
JOHN R. ASHFORD
1. Levin B. Rise of the cigarette police. The Times, June 1, 1992. 2. Ashford JR. Problems in assessing smoking-related mortality. Disorders (in press).
J Smoking-Related
Serological evidence for congenital transmission of human
herpesvirus 6
SIR,-Human herpesvirus 6 (HPV-6) is the causative agent of exanthem subitum.1 Seroprevalence surveys indicate that more than 90% of children have evidence of HHV-6 infection before age 2.2 The virus has been detected in oropharynx and salivary glands of healthy adults, leading to speculation that HHV-6 is transmitted through contact with infected oral secretions.3 The possibility of congenital transmission of HHV-6, in analogy to other human herpesviruses, has been considered.’ We have retrospectively evaluated stored cord-blood specimens for evidence of congenital HHV-6 infection. 799 cord-blood sera were chosen randomly from
Abortion SIR,-Dr Joyce Poole (May 30, p 1340) is slightly confused in her assertions of the views of the Catholic Church on the status of the human embryo. What the Church has repeatedly said is that from the beginning of the fertilisation process the embryo is new human life, and this fact alone should govern its status, dignity, and rights under the law. Justice requires that an equality of respect be given to all human life and not merely because of its characteristics, attributes, or achievements. Poole feels that to describe the embryo as a person is incorrect because it has not had time to develop at least some of the properties of personhood. The Lockean understanding of personhood1 is that of manifest self consciousness and rationality, abilities that develop gradually and continuously by virtue of the potential capabilities of human embryo from conception onwards. But the Church believes it is wrong not to respect human life before it has attained these further properties. If this moral principle of respect for human life is reduced to the level of a subjective preference it would erode the foundations of British and other systems of justice. The Catholic Church has never pronounced that ensoulment occurs at conception. How could it possibly attain to such certitude? The links between contraception and abortion centre on the fact that many of the methods used in contraceptive techniques are abortifacient and that when failures occur abortion is used to take up the slack from inadequate contraception. When the contraceptive pill is used regularly and correctly failure rates of 05-2-0 pregnancies per 100 women years are reported. Used in the big world, however, away from controlled trials with medical supervision, different figures are cited-ie, failures of 2-16% in the USA and over 20% in developing countries. In developing countries, women who stop the pill within a year have an average conception rate of 55%.2 Population growth cannot solely be regulated by widespread use of contraceptive techniques. The late Christopher Tietze of the Population Council in America stated that "barring a major breakthrough in contraceptive technology or major modifications in human sexual behaviour, levels of fertility required for population stabilisation cannot be easily obtained without induced abortion". Louis Newman of the USA Department of Public Health and a former President of the American Gynecologist’s Association has said that "No country can reduce its population growth significantly without resorting to abortion". The disastrous consequences of arbitrary government interference in India and China are widely known. Poole in her great sympathy for the women of Brazil, which we all share, must surely appreciate that profound cultural factors operate in many of the developing countries that are opposed to contraception. They can only be eliminated by education, which in turn is dependent on economic growth. This is the basis of the pleading by the Catholic Church for a greater balance between the economies of the developed and the developing countries. At the same time the Church recognises the need for efficient natural family planning and has directly sponsored clinics and services to this end in 84 countries. Natural family planning depends on acceptance by the family that birth limitation is necessary. Guild of Catholic Doctors,
Brampton House, Hospital of St John and St Elizabeth,
PETER DOHERTY,
London NW89NH. UK
Editor, Catholic Medical Quarterly
1. Lock
J. Identity and diversity: essay concerning human understanding (1694). Reprinted in: Perry J, ed. Los Angeles. University of California Press, 1975: 33-52. 2. Moreno L, Goldman M. Contraceptive failure rates in developing countries. Int Fam Planning Perspec 1991; 17: 44-49.
SiR,—Iwould comment on some of Dr Ryder and Mr Justice’s points (June 20, p 1544) about my report (May 30, p 1340). I am aware that the Church condones so-called natural family planning, though only since 1950; before this, "periodic abstinence" was firmly condemned as frustrating the basic procreative purpose of marriage. Unfortunately, the method has been found to be of very limited use in most developing countries. Father Sean McDonagh, writing from his wide experience as a missionary in the Philippines, reports that "not a single family, even those with daily contact with a
clinic sister, was able effectively to apply the method". Nor was he able to find evidence that any country had been able to reduce its population without using artificial methodsIt is well known, of course, that family limitation has been imposed in China just as it was prohibited in Romania, with equally disastrous results, but this is an indictment of totalitarian regimens not contraceptive clinics. With respect to the term unborn child, I suggest that Dr Ryder might look again at Gray’s Anatomy, in which he will find that the term embryo is not used until the structure that is to become the fetus is formed at about the 14th day: "Only the cells where the two vesicles (the amnio-embryonic and the yolk sac) are in contact with each other contribute to the formation of the actual embryo". Development from the time of fertilisation until this point is referred to as the pre-embryonic period for the good reason that until the embryonic area or shield has formed there is in fact no embryo-far less an unborn child. The term pre-embryo, preferred by Warnock for the first 14 days, rests on firm biological ground. Although the Church does not claim that a person is present from fertilisation, it takes the morally safe course followed by Mr Justice, that the conceptus should be regarded as having human status from the moment of conception. Fertilisation is, however, a process, not a moment, and the only incident that could possibly be regarded as momentary is the penetration of the zona pellucida by a single spermatazoon; the subsequent extrusion of the polar body of the ovum and the merging of the pronuclei of the maternal and paternal gametes can take up to 72 h. Until then the fertilised ovum has not yet acquired the human genome and there is evidence that the process of chromosomal pairing may frequently go wrong. Unsuccessful pairing results in a conceptus that is incapable of developing into a human being; a defective maternal pronucleus, for example, may lead to the formation of a hydatidiform mole which, though it results from fertilisation, can in no way be regarded as human tissue. It is thus not selfevident that the cleaving embryo has, or should be deemed to have, a moral status equivalent to that of the human person2 yet it is on this uncertain premise that the Church bases its condemnation of abortion at however early a stage, as well as a whole range of widely used contraceptive methods. The embryo is a dynamic structure of human cells with a wide potential, but at its earliest stages it cannot properly be said to be the individual human being into which it may come to grow any more than the clay on the potter’s wheel is already a particular pot.3 Ednam East Mill,
Kelso,
Roxboroughshire TD5 7QB, UK
JOYCE POOLE
1. McDonagh S. The greening of the church. New York: Geoffrey Chapman, 1990. 2. Dunstan GR. The status of the embryo: perspectives from moral tradition. London: King Edward’s Hospital Fund for London, 1988. 3. Coughlan M. The Vatican, the law and the human embryo. Basingstoke: Macmillan, 1990.
Calcitonin treatment of osteoporosis in Italy SIR,-As President and past President of the Italian Society of Osteoporosis and as researchers for several years in the study of metabolic bone diseases, we would comment on Dr Magrini and colleagues’ report (Feb 22, p 499). We agree with the financial concern that the widespread use of calcitonin in Italy could cause an excessive rise in public health costs because of occasional misprescribing of the drug by physicians. However, Magrini and colleagues’ doubts about some properties of the drug and their statement that there is no evidence that calcitonin is beneficial in elderly patients are unjustified. Calcitonin has a potent inhibitory effect on bone resorption, binding to specific receptors on osteoclasts. It is effective when given parenterally or by the nasal routed Apart from oestrogens, calcitonin is the only pharmaceutical compound approved by the Food and Drug Administration for the treatment of established osteoporosis in the USA. Magrini’s observation that calcitonin prescriptions in Italy exceed those in other European countries is not surprising since the clinical trials on calcitonin conducted in this country were among the first to contribute important scientific evidence on the effects and efficacy of the product.2 Furthermore, it has not been proven
121
that the results of the drug consumption survey done in Emilia Romagna region can be extrapolated to the whole of Italy. With respect to calcitonin in elderly patients, most open or double-blind, controlled, randomised studies that confirm the drug’s effect on bone mass were done in subjects with established osteoporosis, with a mean age of about 65 years and proven vertebral ttacrures.2.3A large case-control study (MEDOS) on the incidence of risk factors for hip fracture was done in 1989 in Portugal, Spain, France, Italy, Greece, and Turkey, with the collaboration of WHO and the European Foundation for Osteoporosis. The results (presented at the llth international conference on calcium regulating hormones in Florence, in April, 1992) demonstrate that calcitonin combined with calcium significantly reduces the risk of hip fracture. Consequently, if the Emilia Romagna analysis, which indicates that calcitonin treatment lasts on average 45 days, were typical of all regions in Italy, then an increase in the duration of treatment could be recommended to further reduce fractures in elderly patients. The analgesic activity of calcitonin is well known.4,5 Finally, it has been proven that calcitonin inhibits oestrogendependent bone loss, both in physiological menopause6,’ and after oophorectomy,8 and provides an important alternative in the prevention of menopause-related bone loss in women who are unable or unwilling to take oestrogens.I Thus published data are certainly not consistent with Magrini and colleagues’ doubts that calcitonin is among the drugs on the Italian market that are devoid of proven clinical efficacy. Internal Medicine II, Medical Clinic, Università degli Studi di Roma "La
Sapienza",
00161, Rome, Italy,
G. F. MAZZUOLI C. GENNARI
and Istituto di Patologia Medica, Università degli Studí di Siena 1. Consensus
Development Conference: prophylaxis Osteoporosis Int 1991; 1: 114-17.
2. Mazzuoli
G, Passeri M, Gennari C,
et
and
treatment
osteoporosis.
al. Effects of salmon calcitonin in
postmenopausal osteoporosis: a controlled double blind clinical study. Calcif Tissue Int 1986; 38: 3-8. 3. Overgaard K, Riis BJ, Christiansen C, et al. Nasal calcitonin for treatment of established osteoporosis. Clin Endocrinol 1989; 30: 435-42. 4. Gennari C, Agnusdei D, Camporeale A. Use of calcitonin in the treatment of bone pain associated with osteoporosis. Calcif Tissue Int 1991; 49: S9-S13. 5. Lyritis GP, Tsakalakos N, Magiasis B, et al. Analgesic effect of salmon calcitonin in osteosporotic vertebral fractures: a double-blind placebo-controlled clinical study. Calcif Tissue Int 1991; 49: 369-72. 6. MacIntyre I, Stevenson JC, Whitehead MI, et al. Calcitonin for prevention of postmenopausal bone loss. Lancet 1988; i: 900-02. 7 Gennari C, Agnusdei D, Montagnani M, et al. An effective regimen of intranasal salmon calcitonin in early postmenopausal bone loss. Calcif Tissue Int 1992; 50: 381-83. 8. Mazzuoli GF, Tabolli S, Bigi F, et al. Effects of salmon calcitonin induced by ovariectomy. Calcif Tissue Int 1990; 47: 209-14.
on
the bone loss
Deaths from tobacco SIR,-Professor Peto and colleagues’ report (May 23, p 1268) provides indirect forecasts of mortality from smoking in the developed countries. Although more narrow in scope and using a different (and what is claimed to be a more robust) methodology than the study by some of the same authors reported at the Perth World Smoking and Health Conference in 1990, this is nevertheless one of the most ambitious exercises in quantitative epidemiology ever to be published. Since these and similar forecasts are likely to determine public policy, it is important that what will be regarded by decision-makers as expert advice is in fact well-founded. Forecasting is a notoriously fragile process and in view of the widespread scepticism about pronouncements in this field,l it is not unreasonable to look very carefully at the provenance of the latest set of forecasts.
Any forecasting procedure should include assumptions about the underlying relations, which are most conveniently considered in terms of a mathematical model. The resulting forecasts will be determined by the content and structure of the underlying model. However, the biological and physical mechanisms that determine death in man are poorly understood, especially with respect to possible agents such as tobacco. All types of smoking-related disease also arise in people who have never been exposed to tobacco smoke, and it is clear that other influences
or
confounding factors may be
involved. Neither the identity nor the relative importance of such factors in relation to any particular cause of death has been established on a definitive basis, although many associations (which may or may not be causal) have been reported. Nor is it known how the confounding factors may combine with any effects of tobacco to produce changes in the health status of the individual. On general grounds, it is very likely that the set of relevant confounding factors will vary from disease to disease as well as from society to society. Potential confounding factors may themselves be associated with smoking habits. For example, in societies where the smoking habit is well-established (which in general are the only societies for which evidence can be obtained), smoking is associated with low social class. The innate characterisics of the individual must also play a part, but the only available quantitative evidence about these matters is derived from uncontrolled epidemiological studies in which smokers and non-smokers are self-selected groups. There is no reason to suppose that the smoking habit is determined independently of personal characteristics or confounding factors. On all these grounds, it is clear that any model that is devised as a basis for generating forecasts on the basis of available knowledge is tentative. None of the models used by Peto and his colleages in recent publications seem to take account of these complex issues, and no evidence is presented that the simple models that are used do provide a realistic representation of the factors involved. Having summarised the experience of a "survey" population in terms of a mathematical model, Peto et al apply the results with the same model to a different target population, often in a different era and possibly in a different part of the world. This implies that the extent of any hazard associated with smoking is exactly the same in both survey and target populations, as are the confounding factors and the associations between the elements of the model. In view of the likely presence of differences in the properties and amounts of tobacco smoked, in the way the tobacco is smoked, in the confounding variables, and in the self-selection criteria for smoking, this is indeed a major act of faith. Peto’s indirect method of forecasting is thus subject to these general criticisms. In addition, the use of lung cancer rates as a yardstick involves further unsupported and arguably implausible hypotheses, including the assumptions: that lung cancer rates in non-smokers as reported in national statistical returns must be the same in the survey and target populations; that any relation between smoking, confounding factors, and mortality are of the same form for all relevant diseases; and that different types of product affect specific diseases in the same way. Furthermore, the arbitrary halving of the calculated excess risk associated with smoking may be generous to the tobacco industry, but does not seem to have any scientific foundation. A detailed analysis of the difficulties of assessing smoking-related mortality is being published elsewhere2 and will not be repeated here. Nevertheless, with the evident uncertainties of this process, it is impossible to avoid the question as to whether the calculation by any method of forecasts of mortality due to smoking on the basis of available information can ever be a proper foundation for public policy or anything more than an exercise in speculative arithmetic. Ide House, Ide, Exeter EX2 9RB, UK
JOHN R. ASHFORD
1. Levin B. Rise of the cigarette police. The Times, June 1, 1992. 2. Ashford JR. Problems in assessing smoking-related mortality. Disorders (in press).
J Smoking-Related
Serological evidence for congenital transmission of human
herpesvirus 6
SIR,-Human herpesvirus 6 (HPV-6) is the causative agent of exanthem subitum.1 Seroprevalence surveys indicate that more than 90% of children have evidence of HHV-6 infection before age 2.2 The virus has been detected in oropharynx and salivary glands of healthy adults, leading to speculation that HHV-6 is transmitted through contact with infected oral secretions.3 The possibility of congenital transmission of HHV-6, in analogy to other human herpesviruses, has been considered.’ We have retrospectively evaluated stored cord-blood specimens for evidence of congenital HHV-6 infection. 799 cord-blood sera were chosen randomly from
