The study findings suggested no association between BF duration and LDS scores but adjustments for confounders showed a possible protective effect of longer BF duration against delayed language development. Mothers’ age, working status, family income, and children number of siblings were likely to affect the relation between BF duration and language development. Previous studies confirmed that the above variables were potential confounders need to be considered to reveal the relation between BF duration and cognitive development including vocabulary improvement.
In addition, impacts of breastfeeding to cognitive development in post-infancy are still discussed in many studies. Results from previous studies, a meta-analysis, showed that breastfeeding was associated with cognitive development compared to formula feeding . In 2013, a systematic review emphasized confounding factors that might influence the relationship between BF duration and cognitive development . Up until now, studies on BF duration still found various result regarding the best BF duration to influence cognitive and language ability. Studies on BF duration range from less than 6 months, exclusive BF ( 6 months), more than 6 months, 12 months, to more than 12 months. Interestingly, some studies found BF duration 3 to 6 months was enough to support early and late years of children’s language development . Also, previous study confirmed mother who continues 6 months-BF consistently having intelligences (including vocabulary development) increased until children reach 15 years old. Conversely, Iqbal et al studied the association between BF and cognitive and language development suggested the need to lengthen breastfeeding duration to more than 12 months to get significant increase on both cognitive and language development. Similar to our result, although not significant, a trend to BF duration > 18 months seemed to protect children’s language delay. Otherwise, a study that examined cognitive and noncognitive development of children found no association once the children reached five years old. This study also highlighted mothers' education background as an important factor that influence children's cognitive development . It seemed a number of studies about BF duration and cognitive development were influenced by children age and assessment methods used.
In terms of breastfeeding duration and improvement of cognitive ability, there are two mechanisms attributed to this correlation. First, human milk contains a specific fatty acid called PUFA (DHA and ARA) that contribute to the myelination of brain neurons and to support cognitive development.. Secondly, breastfeeding provides emotional intimacy between mother and children that stimulate positive emotional expressions, reduce antisocial and aggressive behavior that related to cognitive development of children.
LDS score is not commonly administered particularly to assess language development for medical and health studies. For example, a number of studies preferred other tools including Receptive and Expressive vocabulary Tests, the Denver Developmental Screening Test, Early Language Milestones (ELM) and the Receptive-Expressive Emergent Language Scale (REEL) to assess children's language development . However, although these language screening tools have been broadly used in the paediatric settings, it does not mean that 'they are not without limitations' . Some questions in these assessment tools could be too vague and leave out the most critical information regarding children's language development. For example, in ELM which seeks children's word production, the tools will only ask parents or carers whether their children able to produce a minimum of 50 words without require them to mention example of words or vocabularies that their children produce. LDS has demonstrated a much more advanced technique in identifying, capturing, and analysing information regarding children language development.
However, it should also be noted here that as because information is exclusively acquired from parents or carers (not the children themselves), their observations on children daily interactions are crucial. Therefore, good observations will enable parents or careers to give rich information for the LDS to provide consistent and comprehensive results regarding children language development. In other words, lack of inputs from the parents or carers will potentially leave out sensitive information that could be useful to predict whether children experience mild language delays or not. For example, when the current study requesting information about children phrase production, about 30% of participant were unable to detailly provided information regarding their children phrase ability. As a consequence, although their children showed good results in their vocabulary production, the inadequate information from phrase productions could reflect other implications.
Strength and limitation
Our study emphasized on a language development by introducing the LDS as an assessment tool to reveal comprehensive information on language development of children aged 18–35 months. In particular, LDS is able to present specific language delay i.e. words and phrases that could guide to a better language therapy for children. Furthermore, LDS is considered as the best tool for measuring children language because of its effectiveness in the assessment and data analysis process which can be personally conducted and analysed by parents, carers or other parties who have interest in children language development .
Several limitations in our study such as small number of subjects and unavailable data on the duration and frequency of each breastfeeding influence the effect of breastfeeding duration on language development. Moreover, we did not obtain data about mothers’ direct vs indirect breastfeeding practices which might have potential influence on children's language development. Lastly, the study employed a cross sectional data approach that only describe single shoot on both variables with no further follow up data.
Implication of study
This study was adding more evidence on the role of breastfeeding duration in language development of children aged 18–35 months, particularly by using LDS tool.