Association between sibship size and allergic diseases in the Glasgow Alumni Study

Abstract

Background: Recent epidemiological studies consistently report an inverse association between sibship size and allergic disease, but evidence from individuals born before the 1980s is inconsistent. As information on relative permanence of this finding may offer clues to its biological explanation, the association between sibship size and allergic disease in individuals born between 1918 and 1952 was investigated. Methods: Cross sectional surveys conducted by the Student Health Service at the University of Glasgow (1948-68) provided data on 14 140 men and women aged 16-30 years at the time of examination. The main outcome measures studied were self-reported asthma, eczema-urticaria, and hay fever. Results: A total of 1677 individuals (11.9%) provided a positive history of at least one of the three allergic diseases: 457 (3.2%) asthma, 594 (4.2%) eczema-urticaria, and 885 (6.3%) hay fever. Compared with those without siblings (reference odds ratio = 1), the odds ratios (95% confidence intervals) for having any allergic disease among those with one, two or three siblings were 0.86 (0.75 to 0.99), 0.80 (0.69 to 0.93), and 0.70 (0.60 to 0.83), respectively (p trend ,0.001). Increasing birth order and low socioeconomic position in childhood were associated with a lower risk of allergy. Adjustment for birth order, year of birth, age, sex, socioeconomic position in childhood, and family history of allergy did not materially alter the results. Conclusions: There is a robust inverse association between sibship size and allergic disease even among people born in the first half of the 20th century. These results favour relatively time-independent explanations for this phenomenon (such as the hygiene hypothesis or parity related changes in the intrauterine environment) over new environmental exposures.

Single parent households and increased child asthma morbidity

“…Still, the trend toward significance stands in contrast to what could be expected by prior research. Though our study is assessing asthma-related reutilization and not presence or absence of atopy, others have found that having more children in the home is associated with a lower likelihood of allergic disorders (consistent with the hygiene hypothesis) [27,28]. One possible inference from our data, therefore, is that dividing a parent’s resources (e.g.…”

Asthma: epidemiology, etiology and risk factors

“…Although this theory has been supported by some studies of allergy prevalence, 83,84 it has been partially refuted by recent studies of asthma prevalence suggesting that although large family size (more than 4 children) is associated with a decreased risk of asthma, birth order is not involved. 85,86 Furthermore, doubt has been cast on simplistic renditions of this hypothesis, in that infections per se cannot explain some epidemiologic patterns (e.g., prevalence rates for allergy and asthma are high in some South American countries, where exposures to infection are higher than in some countries with lower rates of asthma 3 ).…”

Association between number of siblings and cause-specific mortality in the Glasgow alumni cohort study

“…These results suggest that number of siblings is a proxy for early life exposures, other than smoking, that result in higher adult mortality. We previously reported an association between number of siblings and history of allergic diseases in this cohort [13]. It is unlikely that this pattern of risk is due to residual confounding of unmeasured smoking given that there was no association between number of siblings and lung cancer mortality, an outcome with a much stronger association with smoking.…”

“…Number of siblings has been traditionally used as a proxy for two exposures, poor early life socioeconomic circumstances (in industrialized societies) and exposure to early life infections (e.g. for stomach cancer [7] and allergic diseases [13]). These are the main pathways that are hypothesized in this manuscript.…”