A Time-varying Covariate Approach for Survival Analysis of Paediatric Outcomes

Exclusive breastfeeding for the first 3 months of life may reduce the risk of respiratory allergies and some asthma in children at the age of 6 years

AIM

We examined the associations between breastfeeding and respiratory allergies and types of asthma in American children.

METHODS

This longitudinal study used data from mother-infant pairs who took part in the Infant Feeding Practices Study II in 2005-2007 and the Year 6 Follow-Up Study in 2012. The mothers reported breastfeeding practices on a monthly basis for the first year of life, childhood asthma and allergies at age 6 years, and associated factors. Generalised linear models were used in statistical analyses.

RESULTS

Overall, 1177 mother-infant pairs were included in the sample. A third (32.9%) of the children were exclusively breastfed until the age of 3 months and by the age of 6 years 20.8% had been diagnosed with respiratory allergies and 11.3% with asthma. In the multivariable analyses, exclusive breastfeeding for 3 months was associated with a reduced relative risk of respiratory allergies of 0.77 at the age of 6 years. It also reduced the relative risk of asthma to 0.66, but only if the children did not have a family history of asthma.

CONCLUSION

This longitudinal study provided evidence that exclusive breastfeeding for the first 3 months may reduce the risk of respiratory allergies and asthma in children 6 years of age, but concerning asthma, statistical significance was reached only in children without a family predisposition to asthma.

The Relationship of Breastfeeding and Infant Eczema: The Role of Reverse Causation

Aim: Although reverse causation is well known in the breastfeeding-allergy arena, only a few studies have used a valid statistical method to test its occurrence. This study aimed to illustrate reverse causation between eczema and breastfeeding and to examine their effect estimate under this occurrence. Methods: Time-to-event data from the Infant Feeding Practices Study II were used. Model 1: early signs of eczema were modeled as a time-varying covariate to assess reverse causation using survival analysis approach. Model 2 examined the crude and adjusted relative risk between breastfeeding and early signs of eczema using generalized linear model. Results: Overall, 2,350 mother-infant pairs were included. On average, infants with early signs of eczema versus without, breastfed for 5.2 ± 0.2 months compared with 4.10 ± 0.1, respectively. Model 1, an early sign of eczema, was associated with approximately a 16% (95% confidence interval 2-28) reduction in the risk of ceasing breastfeeding indicating reverse causation. Model 2, each month of breastfeeding increased the risk for early signs of eczema by 3%. Conclusion: Modeling early signs of eczema as a time-varying covariate using survival analysis approach detects reverse causation and children with early signs of eczema were breastfed for longer duration. Failure to account for reverse causation may create biased result and a conclusion where breastfeeding increases the risk for early signs for eczema. Future studies should perceive reverse causation by using time-varying covariate in survival analysis approach.

Inequality and Mother's Age as Determinants of Breastfeeding Continuation in Bangladesh

The World Health Organization recommends continuing breastfeeding up to 2 years of age or beyond for sound growth and development of children. In Bangladesh, continuation rates for breastfeeding have recently decreased and effective measures are required to counter this downward trend. Although recent years have seen economic development and reductions in poverty, Bangladesh still has the highest rate of child marriage worldwide. Thus, we aimed to clarify the factors influencing breastfeeding continuation, especially from the perspective of inequality and mother's age in Bangladesh, using data from the Bangladesh Demographic and Health Survey 2011. Event history analyses were performed during a 24-month follow-up period on 7,041 mothers with duration of breastfeeding as the outcome variable, with wealth index (an indicator for inequality) and mother's age used as the main explanatory variables. The results showed that poorer mothers were on the whole more likely to continue breastfeeding through 24 months after childbirth, and younger mothers were less likely to continue breastfeeding particularly past the first year. However, both younger and older mothers continued breastfeeding to the same extent within the first year after childbirth. Mother's age had time-varying effects on breastfeeding continuation, meaning that the effects on breastfeeding continuation were affected by the child's age. These findings imply that policymakers should be aware that efforts to reduce child marriage may increase the rate of breastfeeding continuation beyond the first year after childbirth. In contrast, efforts at poverty alleviation, aimed at preventing child marriage, may decrease the rate irrespective of the child's age.