Do migrant studies help to identify causes of asthma?

Association of immigrant generational status with asthma

OBJECTIVE

We sought to examine whether asthma risk is lower in second-generation immigrants (i.e., Canadian-born children with at least one foreign-born parent) and first-generation immigrants (i.e., foreign-born children) compared with non-immigrants (i.e., Canadian-born children to Canadian-born parents).

METHODS

Data were obtained from the Canadian National Longitudinal Survey of Children and Youth from 1994 to 2008, which measured child health and developmental factors from birth to early adulthood. The sample included 15,799 participants aged 2-26 years. Asthma was defined as diagnosis by a health professional as having asthma, having wheezing or whistling in the chest, or use of medication for asthma.

RESULTS

Prevalence of asthma (defined as a combination of any three factors) was lower in first-generation (32%) and second-generation (34%) immigrants compared with non-immigrants (46%). After controlling for covariates, first- and second-generation immigrants had 0.21 (AOR = 0.21; 95% CI = 0.07-0.67) and 0.19 (AOR = 0.19; 95% CI = 0.09-0.39) lower odds of reporting asthma compared with non-immigrants, respectively. For every year the parent(s) of second-generation immigrants resided in Canada, the odds for asthma increased by 5% (AOR = 1.05; 95% CI = 1.02-1.06).

CONCLUSION

Immigrant children and youth in Canada, regardless of whether they are first- or second-generation, have lower odds for asthma compared with non-immigrants.

Migrant status and childhood hospitalizations for asthma and other wheezing disorders

BACKGROUND

In developed Western settings, asthma is more prevalent among second-generation compared to first-generation migrants. However, these studies are difficult to interpret as they include migrants of various ethnicities and countries of origin.

OBJECTIVE

We assessed the association of parental migrant status with wheezing disorders among children born in Hong Kong, a developed non-Western setting, where many children have migrant parents from mainland China of the same ethnicity.

METHODS

We used Cox regression to examine the adjusted associations of parental migrant status with time to first public hospital admission for asthma, bronchitis and bronchiolitis (International Classification of Diseases, Ninth Version Clinical Modification 466, 490 and 493) from 9 days to 12 years in a population-representative birth cohort of 8327 Chinese children in Hong Kong.

RESULTS

Having both parents as migrants was associated with higher risk of hospitalization for asthma and other wheezing disorders, compared to both parents being Hong Kong born (hazard ratio 1.30, 95% confidence interval 1.05-1.60 from 9 days to 6 years), adjusted for type of hospital at birth, parental history of allergies, mother's age at birth, father's age at birth and highest parental education.

CONCLUSIONS AND CLINICAL RELEVANCE

In the unique, non-Western context of Hong Kong, second-generation migrants had higher risk of hospitalization for childhood wheezing disorders compared to the native population, particularly before 6 years of age. Further study is required to clarify the underlying mechanisms involved.

Increased risk of peanut allergy in infants of Asian-born parents compared to those of Australian-born parents

BACKGROUND

Asian infants appear to be over-represented among patients with clinical food allergy in Australia, but this has not been formally examined at the population level. Any difference in prevalence according to parental country of birth may be secondary to modifiable lifestyle factors. We aimed to quantify (i) differences in the prevalence of peanut allergy by parental country of birth and (ii) contribution of measured environmental exposures to these differences.

METHODS

The population-based HealthNuts study in Melbourne, Australia, screened 5276 infants (74% participation) with skin prick tests and sensitized infants underwent food challenge. Of these, 535 had a parent born in East Asia and 574 in UK/Europe. Associations between parents' country of birth and offspring peanut allergy were examined using multiple logistic regression.

RESULTS

Compared to infants with two Australian-born parents, peanut allergy was more common among infants with parent/s born in East Asia (OR 3.4, 95% CI 2.2-5.1) but not those with parent/s born in the UK/Europe (OR 0.8, 95% CI 0.4-1.5). Paradoxically rates of allergic disease were lower among Asian parents. A higher prevalence of eczema among infants of Asian parents explained around 30% of the increase in peanut allergy, while differences in dog ownership explained around 18%.

CONCLUSIONS

The high peanut allergy prevalence among infants of Asian-born parents appears to have occurred in a single generation and was not present among infants with parents migrating from other countries, suggesting gene-environment interactions are important. The role of eczema and microbial exposure in food allergy prevention warrants exploration.

Etiology of ethnic differences in childhood spirometry

OBJECTIVES

Age- and height-adjusted spirometric lung function of South Asian children is lower than those of white children. It is unclear whether this is purely genetic, or partly explained by the environment. In this study, we assessed whether cultural factors, socioeconomic status, intrauterine growth, environmental exposures, or a family and personal history of wheeze contribute to explaining the ethnic differences in spirometric lung function.

METHODS

We studied children aged 9 to 14 years from a population-based cohort, including 1088 white children and 275 UK-born South Asians. Log-transformed spirometric data were analyzed using multiple linear regressions, adjusting for anthropometric factors. Five different additional models adjusted for (1) cultural factors, (2) indicators of socioeconomic status, (3) perinatal data reflecting intrauterine growth, (4) environmental exposures, and (5) personal and family history of wheeze.

RESULTS

Height- and gender-adjusted forced vital capacity (FVC) and forced expired volume in 1 second (FEV1) were lower in South Asian than white children (relative difference -11% and -9% respectively, P < .001), but PEF and FEF50 were similar (P ≥ .5). FEV1/FVC was higher in South Asians (1.8%, P < .001). These differences remained largely unchanged in all 5 alternative models.

CONCLUSIONS

Our study confirmed important differences in lung volumes between South Asian and white children. These were not attenuated after adjustment for cultural and socioeconomic factors and intrauterine growth, neither were they explained by differences in environmental exposures nor a personal or family history of wheeze. This suggests that differences in lung function may be mainly genetic in origin. The implication is that ethnicity-specific predicted values remain important specifically for South Asian children.