Month of birth and childhood atopic diseases in the tropics

The Association Between Season of Birth and Atopic Dermatitis in the Northern Hemisphere: A Systematic Review and Meta-Analysis

BACKGROUND

Cold and dry climate negatively affects skin barrier functions. This could explain the higher incidence of atopic dermatitis (AD) in Northern countries distant from the equator, as well as the general worsening of AD in Northern European winter months. Although it has been suggested that fall and winter birth is associated with AD, this remains unknown.

OBJECTIVES

To examine whether the prevalence of AD is associated with season of birth.

METHODS

We conducted a systematic review and meta-analysis. Two reviewers independently searched 3 databases. Study quality was assessed using a Newcastle-Ottawa scale. Study heterogeneity was assessed with Cochrane Q and I² statistics. Odds ratios with 95% CIs were calculated. Publication bias was assessed using funnel plots.

RESULTS

The systematic review identified 23 relevant articles of which 9 articles were included in the meta-analysis. Among a total of 726,378 children aged 0 to 12 years, the overall pooled prevalence of AD was 12.9%. The pooled prevalence of AD was 15.4% (95% CI, 12.1%-19.1%), 14.9% (95% CI, 12.0%-18.1%), 12.7% (95% CI, 10.2%-15.4%), and 13.7% (95% CI, 10.8%-17.0%), among children born in the fall, winter, spring, and summer, respectively. AD was significantly associated with fall (odds ratio, 1.16; 95% CI, 1.06-1.28; P = .0018) and winter (odds ratio, 1.15; 95% CI, 1.04-1.27; P = .0076) birth compared with spring birth.

CONCLUSIONS

Although a positive and significant association was observed between being born in fall and winter and developing AD on the Northern hemisphere, there is a need for additional and better-designed studies to understand the effect of seasonal changes on the risk of AD.

Symptoms of allergic rhinitis in women during early pregnancy are associated with higher prevalence of allergic rhinitis in their offspring

BACKGROUND

Epigenetic control of gene expression profiles is a ubiquitous mechanism during cell differentiation, organogenesis and chronic inflammatory reactions. Recent studies have shown that allergen exposure during very early pregnancy increases bronchial hypersensitivity in offspring in a murine model of bronchial asthma. However, no such phenomena were reported in humans. In the present study, the role of epigenetic control in the onset of allergic diseases was investigated.

METHODS

A total of 400 pairs of mothers with physician-diagnosed allergic rhinitis (AR) and their offspring (age 7-18 months) who participated in a large-scale medical check-up were enrolled in this retrospective cohort study. Family history of allergic diseases and the presence or absence of AR symptoms during pregnancy were inquired about using a self-answered questionnaire. A logistic regression model adjusted for age, gender, birth month and father's history of allergic diseases was statistically analyzed.

RESULTS

Offspring whose mothers had any AR symptoms during early pregnancy showed a significantly higher adjusted odds ratio for the onset of AR in offspring than those whose mothers had no symptoms during pregnancy (adjusted Odds Ratio: 6.26, p = 0.036). However, the symptoms of AR during late pregnancy showed no effects on the odds ratio. In contrast, the presence or absence of AR symptoms during early or late pregnancy showed no association with the prevalence of food allergy, atopic dermatitis or asthma in offspring.

CONCLUSIONS

Our results suggest the presence of possible epigenetic mechanisms regulating the onset of AR in humans presumably through increased organ-specific hypersensitivity.

Before-birth climatologic data may play a role in the development of allergies in infants

While an exacerbation in allergic symptoms corresponding to seasons has long been reported, few studies have investigated the association between the season of birth and allergic disorders. The aim of this study was to investigate whether the climatologic data before and after birth affected the incidence of atopic dermatitis (AD) and the results of allergy-related blood tests in early infancy. From February 1995 to January 2000, 2136 infants were tested for AD and followed for 12 months. AD patients were tested by using allergy-related blood tests. Data were compared according to the month of birth and the climatologic data using a computed statistical software package. Six hundred and thirty infants had AD before 12 months old, and significant differences were found according to the season of birth (p < 0.0001). Infants born in spring showed the lowest (22.3%) incidence, while those born in autumn showed the highest (34.6%). In 369 patients, total serum IgE levels, and serum specific IgE levels with egg white at 3 months old were also different according to the season of birth. All of these levels were lower in patients born in spring and summer, and higher in patients born in autumn and winter. Furthermore, the cumulative sunshine amount during the 3 months before and after birth was inversely correlated, while the average temperature over the 3 months before birth was positively correlated to the incidence of AD according to the month of birth. The climatologic data around birth may play an important role in whether an infant develops allergies.

Latitude, birth date, and allergy

BACKGROUND

The space and time distribution of risk factors for allergic diseases may provide insights into disease mechanisms. Allergy is believed to vary by month of birth, but multinational studies taking into account latitude have not been conducted.

METHODS AND FINDINGS

A questionnaire was distributed in 54 centres to a representative sample of 20- to 44-y-old men and women mainly in Europe but also including regions in North Africa, India, North America, Australia, and New Zealand. Data from 200,682 participants were analyzed. The median prevalence of allergic rhinitis was 22%, with a substantial variation across centres. Overall, allergic rhinitis decreased with geographical latitude, but there were many exceptions. No increase in prevalence during certain winters could be observed. Also, no altered risk by birth month was found, except borderline reduced risks in September and October. Effect estimates obtained by a multivariate analysis of total and specific IgE values in 18,085 individuals also excluded major birth month effects and confirmed the independent effect of language grouping.

CONCLUSION

Neither time point of first exposure to certain allergens nor early infections during winter months seems to be a major factor for adult allergy. Although there might be effects of climate or environmental UV exposure by latitude, influences within language groups seem to be more important, reflecting so far unknown genetic or cultural risk factors.