The Possible Modifying Effect of Maternal Age on the Association between Breastfeeding and Autism Spectrum Disorder in Jamaican Children

Background: Breastfeeding, especially for longer than 6 months after birth, has been shown to have medical, developmental and cognitive benefits in children. Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder that occurs in early childhood and has long-term consequences throughout life. Several studies have investigated the possible role of breastfeeding in susceptibility to ASD but some of the findings are conflicting. This could be due to lack of attention to the possible synergic effect of breastfeeding and maternal age in ASD. Since neurodevelopment begins in the first few weeks of gestation and continues into early childhood, and breastfeeding practices may depend on maternal age, it is important to investigate the possible role of maternal age as an effect modifier of the possible association of breastfeeding or its duration and ASD.

Objectives: To investigate the possible role of maternal age as a modifier of the effect of breastfeeding, and its duration in ASD in Jamaican children.

Methods: We used data from the Epidemiological Research on Autism in Jamaica (ERAJ) and ERAJ-2 study, which enrolled 343 pairs of age-(± 6 months) and sex-matched ASD cases and typically developing controls. Conditional logistic regression analyses were performed to assess the possible association of breastfeeding, and its duration with ASD while controlling for potential confounders. Additionally, interactions between maternal age and breastfeeding were explored in relation to ASD. Matched odds ratios (MORs) and 95% confidence intervals (95% CIs) are reported for each of the two levels of the maternal age (i.e., <35 and ≥35 years).

Results: In univariable analysis, we did not find any significant association of being ever breastfed with ASD [MOR = 1.22, 95%CI (0.66-2.28), P =0.528]. Similarly, no significant univariable association was observed between the duration of breastfeeding and ASD when breastfeeding for >3-6, >6-12, and >12 months were compared to ≤3 month of breastfeeding [Overall Wald test P = 0.712, MORs (95% CI): 1.05 (0.68-1.63), 1.17 (0.74-1.86), 0.90 (0.59-1.38), respectively]. However, in the multivariable model, maternal age appeared to be a possible effect modifier for the association between breastfeeding duration and ASD. Specifically, among mothers who were ≥ 35 years of age, the association between breastfeeding duration and ASD was marginally significant when breastfeeding for >3-6, >6-12, and >12 months were compared to ≤3 months of breastfeeding [MOR (95%CI): 0.30 (0.09-1.09), P = 0.067; 0.44 (0.14-1.38), P = 0.159; and 0.35 (0.11-1.12), P = 0.076, respectively]. Whereas, among mothers who were <35 years of age, no statistically significant associations were observed when breastfeeding for >3-6, >6-12, and >12 months were compared to ≤3 months of breastfeeding [MOR (95% CI): 1.19 (0.73-1.94), P = 0.475; 1.23 (0.72-2.09), P = 0.449; and 0.94 (0.59-1.50), P = 0.805, respectively].

Conclusions: Findings from this study imply that Jamaican children whose mothers are 35 years or older may potentially benefit more from breastfeeding for a duration of more than 3 months to protect against ASD compared to those whose mothers are younger than 35 years. These findings require replication in future studies.