Breastfeeding and childhood hospitalizations for asthma: evidence from Hong Kong’s 'Children of 1997' birth cohort

Abstract

Observational studies, largely from Western settings, show that breastfeeding is associated with lower risk of asthma in the first few years of life. Breastfeeding and asthma in Western settings share social patterning, making these observations open to confounding. A cluster randomized trial in Belarus (PROBIT) showed no effect of the promotion of breastfeeding on childhood asthma up to age 6.5 years. However, its generalizability is uncertain. To clarify the role of breastfeeding in asthma, we examined the association of breastfeeding with asthma in a developed non-Western setting with little clear social patterning of breastfeeding or asthma. Using Cox regression, we examined the adjusted association of breastfeeding with public hospital admissions for asthma from birth to 6 years of age in the “Children of 1997” birth cohort, a population-representative prospective cohort of 8,327 Hong Kong Chinese children born in 1997. Children who had been exclusively breastfed for >/=3 months, compared to never breastfed, did not have lower risk of hospitalization for asthma (hazard ratio (HR) 1.25 [95% confidence interval (CI): 0.70, 2.21]), nor did those who had been partially breastfed for any length of time or exclusively breastfed for < 3 months (HR 1.10 [95% CI: 0.80, 1.52]), adjusted for sex, birth weight, gestational age, mode of delivery, birth order, maternal age, secondhand smoke exposure and markers of socioeconomic position. Similar to our previous findings on the associations of breastfeeding with childhood adiposity and blood pressure, our results were consistent with the PROBIT trial, which showed no effect of breastfeeding on the risk of childhood asthma (cluster adjusted odds ratio 1.2 [95% CI: 0.7, 1.9]). These null findings from a developed non-Western setting further indicate that observed associations of breastfeeding and asthma may be contextually specific rather than biologically based.