SMOKING, AIR POLLUTION, AND BRONCHITIS IN BRITAIN

Saturday

SMOKING, AIR POLLUTION, AND BRONCHITIS IN BRITAIN P. M. LAMBERT* D. D. REID Medical Statistics and Epidemiology, London Department of School of Hygiene and Tropical Medicine, London W.C.1

postal survey of the prevalence of respiratory symptoms has been carried out in a large sample of the British population. Analysis of the 9975 replies from men and women aged between 35 and 69 (74% of those presumed able to reply) showed satisfactory agreement with Census and other data. Increasing prevalence with ageing and cigarette consumption has been confirmed. A male Summary

excess

is

seen

A

among non-smokers

Urban/rural gradients

are not

as

well

as

smokers.

explained by smoking

differences alone. Prevalence-rates for symptoms rise with increasing levels of air pollution independently of cigarette consumption. Without cigarette smoking, local pollution seems to have little effect. In smokers, however, high levels of pollution are associated with more frequent respiratory symptoms. The frequency of more serious bronchitis increases most steeply with age among smokers in the more polluted districts. Introduction THE dominant influence of smoking on chronic lung disease is now well recognised; its effect is readily detected in relatively small surveys. To .discern the action of less potent factors in the causation of the disease needs surveys on a scale that may make personal interrogation and examination very expensive if not impracticable. Because the diagnosis of chronic bronchitis largely rests on the presence of symptoms which can be defined, an approach by postal questioning may be considered. Such a postal survey has been carried out in the United States to ascertain the prevalence of chest and heart disease among British and Norwegian migrants and a sample of native-born Americans in 12 States.1-3 Response-rates of 82-94% were obtained from people between the ages of 35 and 74, and the questionaries were adequately completed. To match the results in the sample of people born and living in the United States a similar survey was carried out in Britain in the Spring of 1965. One aim was to detect any specific effect on bronchitis prevalence of circumstances of urban life in Britain such as air pollution in addition to that of cigarette smoking. But we also hoped to establish whether such methods could be effectively used in Britain where people might be less ready to respond to a questionary on personal symptoms sent through the post. *

Present address: General

7652

Register Office, London W.C.2.

25

April

1970

Methods The aim was to replicate, as far as practicable, the methods used in the U.S. surveys. This entailed drawing a representative sample of the population of both sexes between the ages of 35 and 69 living in either England and Wales or Scotland. All the local administrative districts were stratified according to region and degree of urbanisation, and 298 of them were randomly selected from within these strata. Households were then drawn systematically from electoral registers supplemented by rating-lists. Because about 30% of British migrants in the U.S. are of Scottish birth, the sampling fraction used for Scottish districts was increased fourfold. By using a sample prepared in this way (and used earlier for a household survey by a market-research firm) we were able to eliminate many households having no members above the age of 35. We sent a letter to each sampled person over the age of 35 years at the time of the survey enclosing a questionary which included the basic questions from the Medical Research Council questionary on respiratory symptoms4 and the London School of Hygiene questionary on cardiovascular symptoms.5 Details on employment, residential history, marital status, and past and present smoking habits were also requested. On return, questionaries were checked for completeness in defined essential respects and, if necessary, were returned for completion. Up to three letters were sent over the space of 1 month to each householder before we concluded that no response was likely. Where no forwarding address was available through the General Post Office, the aid of the local National Health Service executive council was enlisted to trace those who had moved house. Finally, the homes of a random sample of 289 of those who had not responded were visited in the hope that they could be persuaded to give some details about themselves. Results

Response There

were

18,379

men

and

women

believed

to

be

aged 35 or over in the households sampled. Completed questionaries were returned by 12,236. Of these, 2261 were outside the required age range of 35-69. There were 1155 refusals and no replies from 3614. For various reasons (death, incapacity, gone abroad, or not at the address given) no reply could have been expected from at least 1374. Although the age-distribution of the households approached was not precisely known, it can be estimated from the Census data on the total population of which they were a random sample. On this basis, the 9975 completed questionaries which provide the data for this paper probably represent 74% of all those approached and able to respond in the age-group of 35-69 years. Adequacy of Sample The representativeness of this national sample was tested in several ways. Table i shows that in respect of age, sex, and urban-rural distribution, except perhaps for a poorer response from rural areas, it matches reasonably well the corresponding distributions from

854 TABLE

I-FREQUENCY

DISTRIBUTION OF RESPONDENTS BY DEMOGRAPHIC CHARACTERISTICS

Sex and age from Registrar-Generals’ Statistical Reviews 1965. Urbanisation and social class from 1961 Census (10% sample). Con. = Conurbation. L.u., M.u., and s.u. == Large, medium, and small urban areas. Rur. =Rural area.

the national Censuses (weighted to accord with the Scottish quota in the sample). There is poorer agreement in respect of social class. Because the questionaries asked for occupation " followed for the longest period of time " rather than, as in the Census, at the present time, the proportion in social classes iv and v may be exaggerated. The comparison seen in table 11 shows agreement TABLE II-DISTRIBUTION OF SMOKING HABITS BY SEX COMPARED WITH RESULTS OBTAINED BY TOBACCO RESEARCH COUNCIL

(1966)

sex, age, and

cigarette consumption. Since only 9% of smoked pipes or cigars alone (table n), only cigarette consumption is taken into account in the ensuing tabulations. Table iv and fig. 1 illustrate some important features of the relationship between consumption level and symptom prevalence

the

men

and

no women

in different age and sex groups. In almost every age and smoking-category group there is a male excess in

(%)

TABLE IV-SYMPTOM-PREVALENCE RATES CIGARETTE CONSUMPTION

BY

SEX, AGE, AND

between the distribution of smoking habit as determined by this survey and that in a national sample g survey conducted in 1965.6 Among 88 initial nonresponders later interviewed personally, 20 reported morning phlegm production and 13 reported persistent cough and phlegm production compared with the 22 and 12 cases expected on the basis of the age-sex and smoking-specific rates for all initial responders. We conclude, therefore, that although the sample may not be

completely representative from a national point of view, any bias present is unlikely to affect the relationship in individuals between smoking and other environmental circumstances and the prevalence of respiratory symptoms. Sex, Age, and Cigarette Consumption Table ill gives the distribution of respondents by

frequency of either " persistent cough and phlegm production " (lasting 3 months or more) or chronic bronchitis (persistent cough and phlegm production, breathlessness on walking, and a period of increased cough and phlegm lasting 3 weeks or more in past 3 years). Among those men who have never smoked the

TABLE III-DISTRIBUTION OF RESPONDENTS BY SEX, AGE AND CIGARETTE CONSUMPTION

"

855

there is little rise in symptom frequency with increasing age. With increasing consumption, however, the rise

TABLE V-SYMPTOM-PREVALENCE RATIOS STANDARDISED FOR AGE AND SMOKING BY POPULATION AGGREGATES

with age becomes steeper until in men smoking more than twenty cigarettes a day, the rate falls after reaching a peak between the ages of 55 and 64. In this agegroup are men who started smoking late in life or who have given up because of the onset of symptoms in middle age. The rates for ex-smokers lie between those who have never smoked and those now smoking less than twenty cigarettes a day; but they rise con-

for each

given in table iv. Table v shows that the adjustment for differences in current cigarette consumption reduces but does not remove the trend in bronchitic symptoms between the high rates for the sex

extra

conurbations and low

rates

in rural districts.

Measures of Air Pollution The place of residence of those

surveyed can also be classified according to other speciiic characteristics of the local environment. In the context of bronchitis, prevailing levels of air pollution are certainly relevant. Indices of pollution have therefore been calculated for each of the areas selected in the initial sampling process for which data are available. These were: smoke and sulphur dioxide in 19657and an index based on domestic coal consumption in 1952.8 Unfortunately, only about 30% of our sample lived in areas covered by the National Air Pollution Survey; and sulphur-dioxide measurements were not completely reported even there. On the other hand, the coal-consumption index covered all but 12%. Nevertheless, the trends in prevalence of " persistent cough and phlegm " (table vi) are similar in respect of all three measures of local air pollution. The prevalence ratios for males, which take into account age and current cigarette consumption, rise from lowest values in the least polluted to peak rates in the most polluted districts. Among women, the trend is similar but neither as striking nor as consistent.

of persistent cough and phlegm production in smoking

Fig.l-Prevalence sex, age and

groups.

sistently with age until in women is similar.

over

the age of 65. The pattern

Urban/rural Comparisons Geographical comparisons of symptom prevalence

clearly

must structure and

take into account both the age-sex

smoking-habits of the populations concerned. This has been done by calculating standardised morbidity ratios which compare the number of observed in a group with the number to be expected on the basis of the age-smoking-specific rates cases

TABLE VI-SYMPTOM-PREVALENCE RATIOS

Joint Action of Cigarette Smoking and Air Pollution The scale of this survey allows the tabulation by smoking category of the prevalence ratios (standardised for age) for men and women living in areas with different levels of air pollution. Table vil gives these ratios "for persistent cough and phlegm". Among those who have never smoked, there is a steady increase in symptoms with each rise in local air-pollution level. Similar increases are seen almost uniformly in every smoking group. Although the proportionate rise in prevalence is similar in each group, the absolute difference in risk of morbidity steadily increases with each rise in cigarette consumption. In fig. 2, which summarises

(PERSISTENT

COUGH AND PHLEGM) STANDARDISED FOR AGE AND SMOKING BY AIRPOLLUTION INDICES

Figures in italic type show observed numbers of symptom-positive residential sites in March, 1965 (National Air Pollution Survey).

respondents. Smoke and sulphur dioxide concentrations

are

based

on

values

at

856 TABLE VII-AGE-STANDARDISED SYMPTOM-PREVALENCE RATIOS (PERSISTENT COUGH AND PHLEGM) (%) BY SMOKING AND AIR-POLLUTION LEVEL

pollution districts does not increase with age. On the other hand, the presumed effect of pollution becomes increasingly evident in the rising excess in the more serious type of chronic respiratory disease among those over the age of 45 years. As before, however, the non-smokers living in an area of relatively low pollution show little increase in prevalence with increasing age. The absolute increase in prevalence among older nonsmokers that is associated with residence in a more heavily polluted district is small compared with the corresponding excess in smokers of the same age.

the data on the prevalence of " chronic bronchitis ", the ratio rises in both smokers and non-smokers by about three-quarters of its initial level. But the absolute differences is 30 in non-smokers and 88 in smokers. This widening gap between smokers and non-smokers as pollution increases certainly suggests that the joint influence of pollution and smoking on the level of the prevalence-rate is greater than the sum of their separate effects.

Smoking and Pollution effects

at

TABLE VIII-SYMPTOM-PREVALENCE RATES AND AIR POLLUTION

(%)

BY

AGE, SMOKING

Different Ages

This apparent interaction of smoking and pollution can also be looked at in relation to age. The survey population in different age-groups was divided into smokers and non-smokers and then into two groups according to the level of pollution of their place of residence. The two pollution groups correspond to " " " " very low " or low " and moderate " or high " in the Douglas-Waller classification.8 The prevalence rates of "persistent cough and phlegm" and of " chronic bronchitis " are given in table vm and illustrated in fig. 3. The rates for smokers have been adjusted to allow for differences in the amount smoked at different ages. They show, for " persistent cough and phlegm production ", little difference between those who have never smoked living in the more and less heavily polluted districts even in later life. There

Cross-sectional data of this kind must be interpreted with caution, but the results are consistent with the notion that cigarette smoking produces increased cough and phlegm production in early adult life and that, as those thus affected become older, the cumulative exposure to air pollution rapidly raises the prevalence among them of more serious bronchitic disease. Without the predisposing effect of cigarette smoking, air pollution seems to produce only a small

is, however, a large excess among cigarette smokers, especially those living in these more polluted districts, which is already apparent among those between the ages of 35 and 44 years.

This gap between the

Fig. 2-Prevalence of chronic bronchitis in relation to smoking and air pollution. The absolute numbers of symptom-positive respondents were:

Fig. 3-Age-trends in respiratory disease and air pollution.

in relation to

smoking

857

absolute increase in chronic bronchitis among those the age of 55 years.

over

Discussion

This survey has shown that postal questionaries are an acceptable form of health inquiry in Britain although the response-rate was lower than that obtainable by a personal approach. The lower response-rate achieved here compared with the U.S. surveys may be due in part to the fact that this sample had already been involved in a marketing survey. The validity of the clinical data obtained in this way may be questioned. Some studies have shown considerable agreement between results of postal questionaries and subsequent clinical examination. 9,10 A follow-up of the large numbers of respondents in the U.S. postal survey 11 showed that those reporting persistent cough and phlegm production had a nine-fold increase in mortality from various forms of chronic non-specific lung disease over those not reporting these symptoms. (Provisional results show a similar excess in mortality among respondents reporting these syndromes in the present survey.) This survey is an extension of earlier geographic studies of bronchitis in Britain. 12,13 The large numbers covered by this study have allowed a fairly clear discrimination between the presumptive effects of cigarette smoking and air pollution in the area of residence. Although current cigarette consumption may be fairly precisely reported, the various indices of air pollution in the present place of residence may give at best a poor measure of a lifetime’s exposure in different areas. Because of this imprecision in the measurement of personal exposure, no numerical assessment can be made of the relative contribution made to disease prevalence by either pollution or cigarette smoking. On the other hand, it seems clear that in the absence of smoking the influence of other pollutants in the air is small. There seems to be, indeed, some interaction between these aetiological factors which results in especially high prevalencerates among smokers living in the more heavily polluted areas of this country. From the viewpoint of both individual patients and the public health, it is this absolute rather than the proportionate rise in disease frequency that is important. The urban/rural gradient in morbidity in this survey is more striking among men than in women. This is consistent with the urban/rural pattern of mortality from chronic bronchitis in the two sexes.14 Some of this divergence between the sexes may be constitutional or occupational in origin for, even in non-smokers, prevalence-rates for males are somewhat higher. But any joint action of cigarette smoking and air pollution is likely to be much more important than such factors in determining the very high death-rates from bronchitis among men in the more polluted Neither

REFERENCES 1. Reid, D. D. Nat. Cancer Inst. Monogr. 1966, 19, 287. 2. Pearl, R. B., Levine, D. B., Gerson, E. J. ibid. p. 301. 3. Reid, D. D., Cornfield, J., Markush, R. E., Seigel, D., Pedersen, E., Haenszel, W. ibid. p. 321. 4. Medical Research Council’s Committee on the Ætiology of Chronic Bronchitis. Br. med. J. 1960, ii, 1665. 5. Rose, G. A. Bull. Wld. Hlth. Org. 1962, 27, 645. 6. Todd, G. F. Tobacco Research Council Research Paper no. 1, London, 1966. 7. The Investigation of Air Pollution. National Survey Annual Summary: Table I for the year ended March, 1965. Warren Spring Laboratory, Stevenage, Herts. 8. Douglas, J. W. B., Waller, R. E. Br. J. prev. soc. Med. 1966, 20, 1. 9. Cederlof, R., Jonsson, E., Lundman, T. Arch. environ. Hlth., 1966, 13, 738. 10. McNab, G. R., Slator, E. J., Stewart, C. J. Br. J. prev. soc. Med. 1966, 20, 181. 11. Krueger, D. E., Rogot, E., Blackwelder, W. C., Reid, D. D. J. chron. Dis. (in the press). 12. College of General Practitioners. Br. med. J. 1961, ii, 973. 13. Holland, W. W., Reid. D. D. Lancet, 1965, i, 445. 14. Registrar General’s Decennial Supplement. England & Wales 1961: area mortality tables. Stationery Office, 1967.

THEORETICAL RENAL PHOSPHORUS THRESHOLD IN INVESTIGATION AND TREATMENT OF OSTEOMALACIA C. E. DENT T. C. B. STAMP Medical Unit, University College Hospital, London W.C.1

of theoretical renal threshold (T.R.P.T.) prophosphorus vides a reliable and consistent index of renal tubular phosphate reabsorption. It has proved especially valuable in the investigation of patients with osteomalacia and the study of their response to treatment with vitamin D. Thus hepatic osteomalacia in a patient with chronic cholangiitis was shown to be due to malabsorption of vitamin D, on the basis of clinical and biochemical improvement judged partly by stepwise increments in T.R.P.T., during treatment with intravenous vitamin D2 50 µg. daily. In a second case nutritional rickets was diagnosed in an adolescent with an apparently normal dietary history, by the demonstration of a significant rise in T.R.P.T. after treatment with oral vitamin D2 45 µg. daily. Adult-presenting hypophosphatæmic vitamin-Dresistant osteomalacia was diagnosed in a patient who had had a gastrectomy by the absence of a response in T.R.P.T. to oral vitamin D2 in doses up to

The

Sum ary

5 mg.

measurement

daily. Introduction

areas.

smoking

nor

air

pollution

are

likely

to

all the urban/rural difference in mortality from bronchitis that is so characteristic of Britain. The effect of differences in social-class structure or in recent population changes due to migration may well affect these urban/rural comparisons. Evidence on these points should emerge from further analysis of the material collected in this study.

explain

We thank Mr. Alan Wicken of A.G.B. Limited for help in sampling and data collection and Miss Valerie Detton for computing assistance. We are also most grateful to the respondents who gave us their confidence. This study was supported in part by U.S. Public Health Service grant HE 04775 from the National Heart and Lung Institute. Requests for reprints should be addressed to D. D. R.

METHODS which have been used to study the excretion and reabsorption of phosphate by the kidney include the measurement of phosphate clearance,’ % tubular phosphate reabsorptionphosphate/ creatinine clearance ratio3 phosphorus-excretion index,4 and maximum tubular reabsorptive capacity for phosphate (TmP).5 Anderson6 described a method for the determination of TmP based on a