There is an increasing evidence that exclusive breastfeeding (EBF) up to six-month of age has profound biological effects and important consequences on health and nutritional outcomes of children [1, 2]. The immunological properties of breast milk contribute to ensuring adequate nutritional status, proper growth and develop morbidity prevention capacity in child body [3, 4]. In addition, EBF substantially reduces the risk of morbidity and mortality from infectious diseases by eliminating the chance of contamination from formula milk or other fluids and foods [3].

Although it is now well accepted that EBF is enormously important to infants’ health and nutritional status, the most appropriate age for introducing other food is still debated. Before 2001, the World Health Organization (WHO) recommended introducing solid food at 4–6 months. In 2001 the recommendation was changed to 6 months [5]. This change was, in fact, driven by new evidence about benefits of longer-term EBF against infectious diseases and adequacy of breast milk to meet infants’ nutritional requirements of beyond 4 months of age [6]. However, sometimes the evidence has been questioned [7], and some experts have promoted a less stringent recommendation that is more akin to the pre-2001 WHO policy [8, 9]. Part of this controversy is caused by findings of some individual studies [10]. The debate over the optimal duration of EBF is centered mainly on the choice between the known protective effect of EBF against infectious diseases and the insufficiency of breast milk alone to satisfy babies’ nutritional requirements (known as weanling’s dilemma).

Using nationally representative Bangladesh Demographic and Health Survey (BDHS) data, we examined the effect of termination of EBF during the first 2, 4 and 6 months of birth on a set of adverse health and nutritional outcomes of infants. We also examined the population attributable fraction (PAF) to estimate the percentages of specific health and nutritional outcomes that could have been prevented if EBF was not discontinued during the first 6 months of birth.

The prevalence of diarrhea was 8.3%. Around 42% of babies suffered from fever during the 2 weeks prior to the surveys. The prevalence of ARI was around 18.5%. Overall, almost half of the babies (48.9%) suffered from at least one of these three diseases during the 2 weeks preceding the surveys. The prevalence of stunting and wasting was 18.1 and 17.3%, respectively. Almost 30% of the children were underweight during the survey. Overall, 50% of children were found to have one of the three types of under-nutrition (i.e. stunting, wasting and underweight).

PAFs also show there are protective effects of EBF on adverse health and nutritional outcomes. This protective effect was strongest for diarrhea (27.37%), followed by fever (13.24%) and ARI (8.94%). Overall, around 10% of the reported illness attributable to these three diseases could be prevented if EBF was not discontinued during the first 6 months (Table 2). There were slight protective effects of EBF on under-nutrition; around 6% underweight, 2.21% stunting and 0.56% wasting could be prevented by ensuring EBF during the first 6 months. Overall, around 7% of stunting, wasting or underweight in Bangladesh could have been prevented by ensuring EBF up to 6 months of birth.

Worldwide substantial adverse health and nutritional outcomes are attributed to lack of EBF [23, 24]. Results of this study suggest a protective effect of EBF against diarrhea, ARI and fever. EBF up to 6 months did not seem to cause under-nutrition, rather termination of EBF at 2–4 months were found to be associated with underweight. These findings of EBF with three nutritional outcomes, in fact, suggests that the concern around insufficiency of EBF to fulfill the nutritional requirement is not supported. Therefore, together, our findings suggest EBF up to 6 months is beneficial in protecting babies from infections and sufficient to fulfill the nutritional requirement. Overall, our findings are largely consistent with the recommendation of WHO for EBF during the first 6 months.

Worldwide, diarrhea, fever, ARI and under-nutrition remain the major killers of children under 5 years old (often known as under-five death). Of 10.4 million under-five deaths from preventable causes in developing countries each year, over 50% die due to under-nutrition [25] and 29% due to ARI and diarrhea [26]. These adverse health and nutritional outcomes cause frequent hospitalization, improper physical growth and create a momentum leading to the further morbidity, and frequent school missing [27]. EBF up to 6 months of birth is a feasible and healthy preventive measure against adverse health and nutritional outcomes. In our dataset the overall prevalence of EBF during the first 6 months of birth was 56%, which was 17% higher than the average prevalence of EBF (39%) in developing countries [28]. Clearly, this higher prevalence highlights a public health achievement for Bangladesh. This, however, should not be a reason for complacency, as around 46% of children experience some episodes of diarrhea or ARI during the first year of life and one third of total child death burden is attributed to diarrhea [15]. Therefore, the importance of EBF up to the 6 months of birth is crucial for Bangladesh, as the general hygiene practices and overall sanitation are inadequate.

In our analysis we found EBF up to 6 months could have prevented around 27.37% of reported diarrhea and 8.94% of the ARI cases. These findings are consistent to that reported in the previous literature [16, 17, 29]. Factors associated with the occurrence of diarrhea and ARI are broad – some of them are modifiable [3, 30–32]. The mechanisms through which breastfeeding have protective effects on infectious diseases are multiple. Firstly, human milk has specific immunologic properties that protect the infants from infection [33]. Secondly, the array of antimicrobial, anti-inflammatory, immunomodulatory protection, and bioactive molecules and compounds of breast milk create protections against infection [34]. Thirdly, breast milk promotes mucosal maturation, stimulating neonatal immune systems; limits exposure to the germs from foreign dietary antigens [35, 36].

We found a gradual decrease in the ORs of three durations of EBF (or EBF termination) on diarrhea, fever and ARI. This observation is interesting and important. A reasonable explanation of this gradual duration effect is that babies’ immunity is low soon after their birth. With the help of EBF and natural immunity gradually the body develops prevention capacity. In addition, children without EBF receive foods and drinks which could be contaminated [17, 22], and/or difficult to digest [37]. Particularly in developing countries the lack of hygiene and related knowledge increase this contamination, which is the main reason for high infection rate among children of lower socio-economic background [38]. These factors, together, may explain the gradual protective effects of EBF against infections.

Our findings about little or no significant association of EBF with stunting, wasting and underweight are largely consistent to that from the previous studies conducted in developing countries [39, 40]. The WHO estimates that inappropriate feeding of infant is responsible for one-third of the cases of malnutrition worldwide [41]. Complementary foods are necessary when breast milk alone is no longer able to satisfy the nutritional requirement of the growing infant. Too early or too late introduction may adversely affect the child nutritional status. Particularly in developing countries, an introduction of complementary food too early may cause frequent occurrence of microbial contamination and increase the risk of diarrhea and ARI [39]. Thus the weanling’s dilemma and the risk of morbidity and mortality associated with early introduction of complementary foods are concerns primarily in developing countries. This dilemma divided the public health experts and there are disagreements about the right time of introducing complementary food. Our study findings support EBF during the entire first 6 months, as this protects babies against infections, and that it does not cause insufficient nutritional intake, rather termination of EBF during the first 4 months could cause underweight.

It should be noted here that our study is based on population level data. Thus while our overall findings are supportive of EBF up to 6 months, there may be individual cases or settings where early introduction of complementary foods may deem necessary. For instance, in some developing country settings poverty compels mothers to work outside and far away from home that may necessitate to introduce other foods [42]. In a study in Myanmar, lack of financial resources was also cited as a reason for poor maternal nutrition, leading to reduced breast milk production [42].

The main strength of our study is a population level representative data of recent years and a relatively large sample size. Also exposure and outcome data were collected at the same time by imposing 2 weeks recall period, which is likely to reduce bias [18]. We also adjusted our results for a wide range of socio-demographic and health-related confounders. Moreover, unlike previous literature we provided independent statistics for fever alone. Our study has also some limitations. Our data were cross-sectional, therefore, the relationship is correlational only rather than causal. Secondly, it is possible that the temporal sequence of the early signs of infection and termination of breastfeeding were not adequately appreciated by a subgroup of mothers; infection might have been blamed for the termination of breastfeeding, rather than the reverse (i.e. reverse causality). Data collection within a short duration restricted our scope to take seasonal variation into consideration, which was found important for child morbidities [43, 44]. Also this study does not intend to assess the weanling’s dilemma and the adequacy of nutrition from EBF. Additionally, our data were based on participants’ self-report with no scope of validation by the interviewers. However, an evaluation of Demographic and Health Survey data found that the exposure and outcome variables were reasonably well reported [45].

Lack of EBF up to 6 months of birth has adverse consequences on the health and nutritional status of children. A substantial proportion infectious disease and under-nutrition could be prevented if EBF was ensured up to 6 months after birth. Our findings were consistent to the WHO recommendation regarding the public health benefit of EBF in the first 6 months of birth. We recommend taking further initiatives to promote EBF in general, and tailoring programs to those women who are not practicing EBF, in particular.