The magnitude of the effect of smaller family sizes on the increase in the prevalence of asthma and hay fever in the United Kingdom and New Zealand

doi:10.1016/S0091-6749(99)70323-4

Journal of Allergy and Clinical Immunology

Volume 104, Issue 3, September 1999, Pages 554-558

https://doi.org/10.1016/S0091-6749(99)70323-4 Get rights and content

Abstract

Background: Declining family size is one factor that has been proposed to contribute to increasing asthma and hay fever prevalence, but its relative importance has not been quantified. Objective: Our purpose was to determine the change in asthma and hay fever prevalence that would be expected from the reduction in family size that has occurred in England/Wales and New Zealand over recent decades. Methods: The relative change in family size between 1961 and 1991 in England/Wales and New Zealand was determined from census data for these years. Summary weighted odds ratios were calculated for the associations among birth order, family size, and asthma and hay fever prevalence. The expected increase in the prevalence of asthma and hay fever between 1961 and 1991 resulting from changes in family size was then calculated. Results: The expected relative increase in the prevalence of asthma between 1961 and 1991 as a result of the smaller family size was 1% and 5% for England/Wales and New Zealand, respectively; smaller family size would be expected to increase the prevalence of hay fever prevalence in England/Wales by 4%. Conclusions: Changes in family size over the last 30 years do not appear to explain much of the reported increase in asthma or hay fever prevalence. The contribution that other risk factors have made to these increases could be assessed with use of a similar approach. (J Allergy Clin Immunol 1999;104:554-8.)

Section snippets

METHODS

Data on family size for England/Wales and New Zealand was obtained from the Office of Population Censuses and Surveys¹⁹ and Statistics New Zealand,20, 21 respectively, for the period 1961 to 1991. For the United Kingdom data were available for the birth order of children, expressed as a percentage of children. For New Zealand data were available for the number of children per family, expressed as a percentage, based on all families with children. The relative change in family size over the

RESULTS

The studies included in the analysis are shown in Table I.

. Characteristics of studies included in analysis

Study	Country	Study design	Population (y)	Sample size	Outcome measure
Leadbitter et al³³	New Zealand	Cohort	13	734	Asthma ever
Wickens et al³⁴	New Zealand	Case-control	7-9	233 cases/241 controls	Diagnosed asthma and current medication use
Shaw et al³⁵	New Zealand	Cross-sectional	8-13	708	Current wheeze
Moyes et al³²	New Zealand	Cross-sectional	6-7	2,614	Diagnosed asthma
Lewis et al³⁶	England, Scotland, and Wales	Cohort	16

DISCUSSION

Although most studies show an increase in asthma and hay fever prevalence over time, estimating the relative size of this increase between the years 1961 and 1991 (when government statistics were available on family size) is difficult because of the different dates at which point prevalences are reported. For example, no studies were located that reported asthma symptom or hay fever prevalence at 1961 and at 1991. However, a Scottish study¹ reported an increase in wheeze prevalence from 10.4%

Acknowledgements

We thank Dr Christopher D. Moyes for providing us with more detailed data than was reported in his publication.³²

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We analyzed data from Vancouver, Canada, and from Guangzhou, Beijing and Hong Kong, China, collected during phase 3 of the International Study of Asthma and Allergies in Childhood. We subdivided the Vancouver adolescents according to whether they were Chinese immigrants to Canada, Canadian-born Chinese or Canadian-born non-Chinese. We compared the prevalence of asthma and wheezing among Chinese adolescents born in Canada, Chinese adolescents who had immigrated to Canada and Chinese adolescents living in China.
Of 7794 Chinese adolescents who met the inclusion criteria, 3058 were from Guangzhou, 2824 were from Beijing, and 1912 were from Hong Kong. Of 2235 adolescents in Vancouver, Canada, 475 were Chinese immigrants, 617 were Canadian-born Chinese, and 1143 were Canadian-born non-Chinese. The prevalence of current wheezing among boys ranged from 5.9% in Guangzhou to 11.2% in Canadian-born Chinese adolescents. For girls, the range was 4.3% in Guangzhou to 9.8% in Canadian-born Chinese adolescents. The prevalence of ever having had asthma ranged from 6.6% to 16.6% for boys and from 2.9% to 15.0% for girls. Prevalence gradients persisted after adjustment for other environmental variables (odds ratios for ever having had asthma among Canadian-born Chinese compared with native Chinese in Guangzhou: 2.72 [95% confidence interval 1.75–4.23] for boys and 5.50 [95% confidence interval 3.21–9.44] for girls; p < 0.001 for both). Among Chinese adolescents living in Vancouver, the prevalence of ever wheezing increased with duration of residence, from 14.5% among those living in Canada for less than 7 years to 20.9% among those living their entire life in Canada. The same pattern was observed for the prevalence of ever having had asthma, from 7.7% to 15.9%.
Asthma symptoms in Chinese adolescents were lowest among residents of mainland China, were greater for those in Hong Kong and those who had immigrated to Canada, and were highest among those born in Canada. These findings suggest that environmental factors and duration of exposure influence asthma prevalence.
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The magnitude of the effect of smaller family sizes on the increase in the prevalence of asthma and hay fever in the United Kingdom and New Zealand☆,☆☆,★

Abstract

Section snippets

METHODS

RESULTS

DISCUSSION

Acknowledgements

Curr Opin Immunol

J Allergy Clin Immunol

Lancet

Lancet

J Allergy Clin Immunol

Respiratory symptoms and atopy in Aberdeen schoolchildren: evidence from two surveys 25 years apart

BMJ

Increasing asthma prevalence in a rural New Zealand adolescent population: 1975-89

Arch Dis Child

Changes in asthma prevalence: two surveys 15 years apart

Arch Dis Child

Trends and severity of childhood asthma

BMJ

Increasing prevalence of asthma in children

N Z Med J

The change in prevalence of wheeze in seven year old children over 19 years

N Z Med J

The home environment and asthma symptoms in childhood: two population based case-control studies 13 years apart

Thorax

Investigation into the increase in hay fever and eczema at age 16 between the 1958 and 1970 British birth cohorts

BMJ

Secular trends in the occurrence of asthma among children and young adults: critical appraisal of repeated cross sectional surveys

BMJ

Changing patterns of childhood infection and the rise in allergic disease

Clin Exp Allergy

The inverse association between tuberculin response and atopic disorder

Science

Increase in asthma: a more toxic environment or a more susceptible population?

Thorax

Asthma and allergy—disorders of civilization?

Q J Med

Asthma and indoor exposure to allergens

N Engl J Med

Passive smoking as a risk factor for development of obstructive respiratory disease and allergic sensitization

Allergy