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Mark N Upton a Department of General Practice, University of
Glasgow, Glasgow G12 0RR, b Department of
Immunology, Western Infirmary, Glasgow G11 6NT, c Department of Public Health,
University of Glasgow, Glasgow G12 8RZ, d Department of Social Medicine, University of Bristol, Bristol
BS8 2PR
Correspondence to: M N Upton, Thornaby and Barwick
Medical Group, The Health Centre, Thornaby, Cleveland TS17 0BZ marknupton{at}aol.com
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Abstract |
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Objective:
To estimate trends between 1972-6 and 1996 in the prevalences of asthma and hay fever in adults.
The prevalence of asthma has increased in children during
the past few decades.
1 2
As childhood asthma may persist
or recur during adulthood, an increasing prevalence of asthma in adults
is expected as cohorts of children increasingly affected by asthma
become older. Studies of students3 and
conscripts4 suggest that the prevalence of asthma is
rising in young adults, but little information exists at older ages.
Methodological questions often dominate the interpretation of secular
trends.5 To minimise bias, the same survey instrument should be used on two or more occasions in populations that are defined
as far as possible in the same way. As there is no test for asthma, the
detection of secular trends relies on questionnaires. Changes in
awareness and diagnosis of asthma may influence trends detected by
questionnaire, so it is important to ask about symptoms. In older
populations, however, cigarette smoking makes it difficult to attribute
symptoms to asthma.6
We compared the prevalence of asthma and hay fever, and the combined
prevalence of recognised and unrecognised asthma, in two generations of
men and women aged 45 to 54 years. Both generations had taken part in
the Midspan family study in Renfrew and Paisley, in the west of
Scotland; the older generation had taken part in 1972-67
and the younger generation (the offspring) in 1996.8
Sampling
Design:
Two epidemiological surveys 20 years
apart. Identical questions were asked about asthma, hay
fever, and respiratory symptoms at each survey.
Setting:
Renfrew and Paisley, two towns in the west of Scotland.
Subjects:
1477 married couples aged 45-64 participated in a general population survey in 1972-6; and 2338 offspring aged 30-59 participated in a 1996 survey. Prevalences were compared in 1708 parents and 1124 offspring aged 45-54.
Main outcome measures:
Prevalences of asthma, hay
fever, and respiratory symptoms.
Results:
In never smokers, age and sex standardised prevalences of asthma and hay fever were 3.0% and 5.8% respectively in 1972-6, and 8.2% and 19.9% in 1996. In ever smokers, the
corresponding values were 1.6% and 5.4% in 1972-6 and 5.3% and
15.5% in 1996. In both generations, the prevalence of asthma was
higher in those who reported hay fever (atopic asthma). In never
smokers, reports of wheeze not labelled as asthma were about 10 times
more common in 1972-6 than in 1996. With a broader definition of asthma
(asthma and/or wheeze), to minimise diagnostic bias, the overall
prevalence of asthma changed little. However, diagnostic bias mainly
affected non-atopic asthma. Atopic asthma increased more than twofold
(prevalence ratio 2.52 (95% confidence interval 1.01 to 6.28)) whereas
the prevalence of non-atopic asthma did not change (1.00 (0.53 to 1.90)).
Conclusion:
The prevalence of asthma in adults has
increased more than twofold in 20 years, largely in association with
trends in atopy, as measured indirectly by the prevalence of hay fever. No evidence was found for an increase in diagnostic awareness being
responsible for the trend in atopic asthma, but increased awareness may
account for trends in non-atopic asthma.
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Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
![]()
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
Parents
All residents of Renfrew and Paisley aged 45 to 64 years were invited in 1972-6 to complete a questionnaire and attend a cardiorespiratory examination; 15 406 men and women participated (response rate 78%),7 among whom there were
4064 married couples.
Offspring were identified by writing to survivors
in the couples who had participated. Where records showed that husband
and wife had both died, permission was obtained from the privacy
committee of the registrar general for Scotland to write to the death
certificate informant.9 Addresses of survivors or
informants were available for 3445 couples, and replies were received
from 2841. We identified 4829 offspring aged 30-59 years from up
to 2365 couples with children (the precise number is unknown because 200 couples did not want to take part in the pilot study in
which we traced offspring); 3202 offspring from 1767 families lived
locally and formed the eligible population. In 1996 these offspring
were invited to complete a questionnaire and attend a cardiorespiratory
examination at a community clinic.8 In all, 1040 male and
1298 female offspring from 1477 families participated (response rate
for individuals was 73% and for families was 84%). Approval for the
study was obtained from appropriate local research ethics committees.
Survey methods
The following questions, extracted or adapted from the
1965-6 version of the Medical Research Council's
questionnaire,10 were asked at both surveys:
Analysis
Statistical procedures were performed in
STATA.13 Prevalences were directly standardised for age in
five year age groups. We used logistic regression to adjust for age
when testing the significance (P<0.05) of differences between parents
and other participants. We estimated prevalence ratios (95% confidence
intervals) between generations using logistic regression, adjusting for
age, sex, and other covariates as indicated, and for familial
clustering. Any effect of clustering will be small because the mean
number of offspring (aged 45-54) per family was 1.3.
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Results |
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The ages of parents and offspring mainly overlapped at 45-54. In 1972-6, 7897 participants aged 45-54 had complete data, of whom 1708 were parents of offspring who participated in 1996. Of 2338 participant offspring, 1124 were aged 45-54 with complete data. At ages 45-49 and 50-54 there were respectively 213 and 524 fathers, 443 and 528 mothers, 322 and 172 sons, 405 and 225 daughters. The total number of participants was therefore 2832.
Selection of parents
The prevalences of hay fever, asthma, wheeze, chronic
sputum, and breathlessness were lower in the family study parents
compared with those of other participants in 1972-6, but only the
difference for wheeze in women was significant (table 1). Differences
in the prevalence of symptoms between parents and other participants
participating in 1972-6 were largely explained by differences in
smoking and social class (data not shown).
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Changes in prevalence of respiratory illness, smoking, and social
class
Table 2 shows the changes in the prevalences of respiratory
illness, smoking, and social class during the 20 year interval. The
prevalences of hay fever and asthma increased: for hay fever, from
5.4% and 5.8% in men and women respectively in 1972-6 to 15.4% and
20.0% in 1996; for asthma, from 1.4% and 2.8% in 1972-6 to 4.9% and
8.0% in 1996. In both generations the prevalence of asthma was higher
in participants with hay fever. Despite the increased prevalence of
asthma in the 1996 survey, the prevalence of wheeze had decreased in
men and women, as had the prevalences of chronic sputum and
breathlessness. The prevalence of current smoking halved in men and
women between 1972-6 and 1996. The proportion of men and women who were
manual workers also fell.
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"Ever asthma," current asthma, and wheeze
Of the participants with asthma, 40% (16/40) and 16%
(12/76) reported wheeze most days in 1972-6 and 1996 respectively. Participants in 1972-6 were not asked about medication. Improvements between surveys in the treatment of asthma, however, may explain the
reduction in the prevalence of wheeze in those who reported asthma:
47% (36/76) of asthmatic participants reported using inhaled corticosteroids in 1996. Although wheeze was the symptom most strongly
associated with asthma, the observation at both surveys that fewer than
half of the asthmatic participants reported wheeze probably also
reflects the severity of the definition of wheeze (most days) and the
use of "ever" rather than "current" asthma. In 1996, 62%
(47/76) of participants with ever asthma had current asthma according
to the criteria of the European Community respiratory health
survey
that is, they were receiving medication for asthma or had
experienced an attack of asthma in the previous 12 months, or both of
these. Of these 47 participants, 23%11 reported wheeze most days and 81%38 reported wheeze at some time during
the previous year.
Prevalence changes stratified by smoking
Table 3 shows the changes in prevalence of respiratory
illness by smoking status. The prevalences of asthma and hay fever
increased between surveys irrespective of smoking: fully adjusted
prevalence ratios for hay fever were 3.53 (95% confidence interval
2.30 to 5.43) and 2.76 (1.91 to 3.98) in never and ever smokers
respectively, and those for asthma were 2.60 (1.41 to 4.80) and 2.69 (1.49 to 4.84). In never smokers the prevalence of wheeze was lower in
1996 than in 1972-6 (0.32 (0.11 to 0.90)), whereas the prevalences of
chronic sputum and breathlessness were unchanged. In ever smokers the
prevalence of symptoms changed little between surveys. In combined data
for never and ever smokers, including adjustments for smoking status
and pack years, the fully adjusted prevalence ratio for wheeze was 0.68 (0.48 to 0.99).
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Diagnostic bias
Ten times as many never smokers reported wheeze but not
asthma in 1972-6 (3.4%17) compared with 1996 (0.3%2). This finding is based on small numbers, but a
similar age standardised proportion of never smokers reported wheeze
but not asthma in the entire 1972-6 survey (3.5% (74/2345)). In 1996, none of the never smokers who denied asthma or wheeze reported using
inhaled corticosteroids, so the low prevalence of wheeze that was not labelled as asthma was unlikely to be due to treatment. To minimise diagnostic bias we combined participants with asthma with those who
reported wheeze (whether or not they reported asthma) as a new group
(asthma and/or wheeze). Whereas the prevalence of reported asthma
increased more than twofold between surveys, the prevalence of reported
asthma and/or wheeze in never smokers changed little (fully adjusted
prevalence ratio 1.40 (0.83 to 2.36)).
Hay fever and asthma
Clinicians and epidemiologists often use hay fever as a
marker of atopy. Table 3 shows the prevalence of asthma in participants
with and without hay fever, estimated by using individuals in each
stratum as denominator. Asthma increased between the surveys in those
without but not with hay fever (heterogeneity test P=0.02). Even though
asthma was no more frequent at the later survey in those with hay
fever, the increased prevalence of hay fever in the whole population
resulted in an increased proportion of the population who reported both
asthma and hay fever (atopic asthma). We estimated prevalence trends
for atopic and non-atopic asthma in never smokers. Using the narrow
definition of asthma, table 4 shows an increased prevalence of atopic
and non-atopic asthma between 1972-6 and 1996. However, using the broad
definition (asthma and/or wheeze) only atopic asthma increased between
surveys. Diagnostic bias therefore mainly affected non-atopic asthma.
Findings were unchanged when we restricted the analysis to parents and married offspring or substituted all participants of the 1972-6 survey
for the parents (data not shown).
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Discussion |
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Methodology
Parents participated in a general population survey with a
high response.7 Families in which two generations participated were not randomly drawn from all families in Renfrew and
Paisley because the combination of a successful response to offspring
tracing9 in 1993-4 and offspring
participation8 in 1996 retrospectively "selected"
couples who were healthier than the general population. Absolute
prevalences of respiratory illness in parents slightly underestimate
those in the general population survey, but it is reasonable to expect
intergenerational trends in these families to follow trends in the
general population. It is likely that we underestimated the lifetime
prevalence of asthma and hay fever because recall tends to reflect
prevalence over a shorter time period.14 We asked
identical questions about respiratory illness at both surveys but did
not measure bronchial responsiveness or atopy.
Main findings
We found a twofold to threefold increase between 1972-6 and
1996 in the prevalences of lifetime asthma and hay fever reported by
adults aged 45-54, irrespective of smoking. In never smokers, reports
of wheeze not labelled as asthma were about 10 times more common in
parents and all participants of the general population survey in 1972-6 compared with offspring in 1996. In view of the increased professional
and public awareness of asthma since the 1980s,15 our
findings probably reflect underrecognition of asthma 20 years ago. To
assess the effect of possible diagnostic bias, and also confounding by
cigarette smoking, we reviewed trends in the prevalence of any report
of asthma and/or wheeze in never smokers. Little difference existed
between parents and offspring in the prevalence of this broader
definition of asthma. Subgroup analysis showed that the increased
clinical recognition of asthma had occurred in non-atopic rather than
atopic participants (using the presence of hay fever as a marker of
atopy). Based on our broader definition of asthma, the prevalence of
non-atopic asthma did not change between 1972-6 and 1996, but the
prevalence of atopic asthma increased more than twofold.
Comparison with other studies
Few opportunities exist for comparing prevalences of asthma
and hay fever at an interval of 20 years in older adults because most
epidemiological studies during the 1970s focused on cardiovascular
disease and chronic bronchitis. To our knowledge this is the first
population study of secular trends of respiratory illness in older
adults that is stratified by smoking. Fleming and
Crombie16 reported twofold rises in consultation rates for asthma and hay fever in British general practices at all ages between
1970-1 and 1980-1, but lack of information about smoking and symptoms
may have biased this study16 and other studies based
solely on healthcare records. In repeated Australian
surveys,17 hay fever increased between 1981 and 1990, but
the prevalences of wheeze and diagnosed asthma increased only in those
aged below 40. Reviewing British population studies, Cook et
al6 reported that the prevalence of chronic sputum, but
not wheeze, had fallen in line with decreased smoking and suggested
that wheeze may have been sustained by factors related to asthma that
were increasing. In our study, reports of wheeze most days decreased
over time (despite increased asthma) and fewer asthmatics reported
wheeze in 1996 than in 1972-6. This may be the result of improved
asthma treatment. Although we did not record medication in 1972-6, primary care corticosteroid prescriptions for asthma increased more
than sixfold between 1980 and 1990.18
Heterogeneity of asthma
Without objective measurements we cannot be certain that
the prevalence of atopy increased between surveys, nor can we validate
the atopic status of the groups with and without hay fever. Strong
positive associations between hay fever and asthma at both surveys
support the validity of hay fever as an atopic marker, but relations
between asthma, hay fever, skin test reactivity, and immunoglobulin E
are complex.
19 20
The heterogeneity of asthma in children
is well recognised, but in studies of respiratory disease in adults
asthma is often considered as a single entity to be distinguished from
emphysema and chronic obstructive pulmonary disease.
20 21
Studies that have used atopic markers to subdivide asthma in adults
have shown differences in rate of decline of lung
function22 and mortality.23 It is therefore
important to investigate which asthma phenotypes are becoming more
common. Our results are consistent with reported increases in
prevalence of atopic, rather than non-atopic, wheeze in
children.24
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What is already known on this topic
The prevalences of asthma and atopy have increased in children, university students, and conscripts during the past few decades, but little information exists about trends at older ages Prevalence trends detected by questionnaire are vulnerable to biases, including information bias from changed awareness and diagnosis of asthma What this study addsThe prevalence of asthma in adults has increased more than twofold in 20 years, largely in association with trends in atopy (indexed by hay fever) No evidence was found for increased diagnostic awareness being responsible for the trend in atopic asthma, but increased awareness may account for trends in non-atopic asthma |
Conclusion
The prevalence of asthma in adults has increased more than
twofold in 20 years, largely in association with trends in atopy, as
measured indirectly by the prevalence of hay fever. Greater diagnostic
awareness does not seem to be responsible for the trend in atopic
asthma, but increased awareness may account for trends in non-atopic asthma.
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Acknowledgments |
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We thank Victor Hawthorne, who initiated the original Renfrew and Paisley study; the people of Renfrew and Paisley who participated; and Pauline MacKinnon and David Hole for ongoing contributions to the original study. We also thank the following people, who contributed in 1996: Catherine Ferrell, who traced offspring and led recruitment;, Jane Goodfellow, Michere Beaumont, and Helen Richards, who contacted participants; Claire Bidwell, who led the fieldwork; Julie Hunter, Evelyn Lapsley, Iona MacTaggart, Nicola McPherson, and Sarah Morgan for questionnaire checking; Gordon Harley for team building; Lisa Schwartz for ethical advice to participants; Alistair Carson for database development; the patients at Blantyre Health Centre who completed pilot questionnaires; staff at the Robertson Centre for Biostatistics who coded and double-entered data; staff at the Paisley YMCA and Gartnavel Hospital for generous support and use of premises; Caroline Morrison for advice about fieldwork; the scientific advisory committee for its support; Peter Burney for advice about questionnaires; David Strachan for invaluable comments about an early draft of the paper; and Deborah Jarvis (the independent reviewer) for her comments.
Contributors: GCMW conceived the idea for the Midspan family study. GCMW and GDS conceived the 20 year comparison of respiratory disease. MNU designed the questionnaire and supervised fieldwork in 1996. Victor Hawthorne and CRG supervised fieldwork in 1972-6. MNU conceived and performed the analysis and wrote the first draft of the paper. CMcS supported MNU with early drafts. AMcC checked the analysis and managed the 1996 database. CLH managed the 1970s database. All authors contributed to data interpretation and revisions to multiple drafts of the manuscript. MNU is guarantor for the paper.
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Footnotes |
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Funding: MNU and the fieldwork were supported by the Wellcome Trust. AMcC and some of the nurses were supported by the NHS Research and Development programme.
Competing interests: None declared.
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References |
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| 1. |
Anderson HR, Butland BK, Strachan DP.
Trends in prevalence and severity of childhood asthma.
BMJ
1994;
308:
1600-1604 |
| 2. |
Burr ML, Butland BK, King S, Vaughan-Williams E.
Changes in asthma prevalence: two surveys 15 years apart.
Arch Dis Child
1989;
64:
1452-1456 |
| 3. |
Bruce IN, Harland RW, McBride NA, MacMahon J.
Trends in the prevalence of asthma and dyspnoea in first year university students, 1972-89.
Q J Med
1993;
86:
425-430 |
| 4. | Haahtela T, Lindholm H, Bjorksten F, Koskenvuo K, Laitinen LA. Prevalence of asthma in Finnish young men. BMJ 1990; 301: 266-268. |
| 5. |
Magnus P, Jaakkola JJK.
Secular trends in the occurrence of asthma among children and young adults: critical appraisal of repeated cross-sectional surveys.
BMJ
1997;
314:
1795-1799 |
| 6. | Cook DG, Kussick SJ, Shaper AG. The respiratory benefits of stopping smoking. J Smoking-Related Dis 1990; 1: 45-58. |
| 7. |
Hole DJ, Watt GCM, Davey Smith G, Hart CL, Gillis CR, Hawthorne VM.
Impaired lung function and mortality risk in men and women: findings from the Renfrew and Paisley prospective population study.
BMJ
1996;
313:
711-716 |
| 8. | Upton MN, Watt GCM, Davey Smith G, McConnachie A, Hart CL. Permanent effects of maternal smoking on offsprings' lung function. Lancet 1998; 352: 453[CrossRef][Medline]. |
| 9. |
Davey Smith G, Hart C, Ferrell C, Upton M, Hole D, Hawthorne V, et al.
Birth weight of offspring and mortality in the Renfrew and Paisley study: prospective observational study.
BMJ
1997;
315:
1189-1193 |
| 10. | Medical Research Council. Definition and classification of chronic bronchitis for clinical and epidemiological purposes. Lancet 1965; 1: 775-779[Medline]. |
| 11. | Burney P, Chinn D, Jarvis C, Luczynska C, Lai E. Variations in the prevalence of respiratory symptoms, self-reported asthma attacks, and use of asthma medication in the European Community respiratory health survey (ECRHS). Eur Respir J 1996; 9: 687-695[Abstract]. |
| 12. | Registrar General. Standard occupational classifications. London: HMSO, 1966, 1991. |
| 13. | Stata Corporation. Stata Statistical Software. Release 5.0. College Station, Texas: SC, 1997. |
| 14. | McWhorter WP, Polis MA, Kaslow RA. Occurrence, predictors and consequences of adult asthma in NHANES1 and follow-up survey. Am Rev Respir Dis 1989; 139: 721-724[Medline]. |
| 15. | Speight ANP, Lee DA, Hey EN. Underdiagnosis and undertreatment of asthma in childhood. BMJ 1983; 286: 1253-1256. |
| 16. | Fleming DM, Crombie DL. Prevalence of asthma and hayfever in England and Wales. BMJ 1987; 294: 279-283. |
| 17. | Peat JK, Haby M, Spijker J, Berry G, Woolcock AJ. Prevalence of asthma in adults in Busselton, Western Australia. BMJ 1992; 305: 1326-1329. |
| 18. | Central Health Monitoring Unit, Department of Health. Asthma: an epidemiological overview. London: HMSO, 1995. |
| 19. | Burrows B, Martinez FD, Halonen M, Barbee RA, Cline MG. Association of asthma with serum IgE levels and skin-test reactivity to allergens. N Engl J Med 1989; 320: 271-277[Abstract]. |
| 20. |
Pearce N, Pekkanen J, Beasley R.
How much asthma is really attributable to atopy?
Thorax
1999;
54:
268-272 |
| 21. | Vermeire PA, Pride NB. A "splitting" look at chronic nonspecific lung disease (CNSLD): common features but diverse pathogenesis. Eur Respir J 1991; 4: 490-496[Abstract]. |
| 22. |
Ulrik CS, Backer V, Dirksen A.
A 10 year follow up of 180 adults with bronchial asthma: factors important for the decline in lung function.
Thorax
1992;
47:
14-18 |
| 23. | Burrows B, Bloom JW, Traver GA, Cline MG. The course and prognosis of different forms of chronic airways obstruction in a sample from the general population. N Engl J Med 1987; 317: 1309-1314[Abstract]. |
| 24. |
Russell G, Helms PJ.
Trends in occurrence of asthma among children and young adults.
BMJ
1997;
315:
1014-1015 |
(Accepted 14 April 2000)