The present study was designed to assess the relationship between breastfeeding duration and nutritional status among children aged 0 to 23 months. Among Zambian infants and young children, breastfeeding duration was inversely associated with HAZ after controlling for potential child, maternal and household confounders. Other than breastfeeding duration, birth weight was the strongest predictor of HAZ among children under the age of 24 months. Additionally, being female was positively associated with HAZ. Using stunting as an outcome variable, breastfeeding duration increased the odds of stunting among children. Similar findings were observed between breastfeeding duration and WHZ. Apart from breastfeeding duration, birth weight and child sex were the other variables significantly associated with both HAZ and WHZ. Diarrhea episode in the previous two weeks was only associated with WHZ.
Our finding that duration of breastfeeding is negatively associated with nutritional status among children is in line with findings from other low- and middle-income countries. In a prospective cohort study conducted by Fall, Sachdev (16), breastfeeding duration was negatively correlated with HAZ among South African and Filipino infants and young children. Similarly, among Pakistani (17) breastfeeding duration was negatively associated with lower HAZ and height respectively among children. In an earlier analysis, Caulfield, Bentley (11) also observed a positive association between prolonged breastfeeding and malnutrition among child less than three years old. Our results on breastfeeding duration and HAZ are not in agreement with findings among Nepalese (18) and Guatemalan (16) children, in whom breastfeeding duration was shown to be positively associated with HAZ. The differences in the results could be due to failure to account for confounding in some studies or mediating factors such as age of the children. It may as well be due to reverse causality, children perceived to be smaller and shorter are likely to be breastfed longer than their taller counterparts (13, 19). In the present study we controlled for potential confounding and we explored mediation as well as possibility for reverse causality using path analysis. The latter was not evidence in our study.
Our study demonstrates that being female among Zambian children under the age of 24 months was associated with greater HAZ. Similar findings have been reported among African countries. In a meta-analysis on the determinants of stunting and obesity among children in sub-Saharan Africa, Keino, Plasqui (20) demonstrated higher prevalence of stunting among boys than girls, confirming what was reported by Wamani, Astrom (21). The similar findings have recently been observed in Tanzania (22) and Ethiopia (23). The differential sex growth may be related to differences in feeding and care practices for boys and girls or morbidity, the former was observed among Senegalese children younger than three years (24). There is also some evidence that the differences may be linked to differences in the biology of growth between boys and girls (25). Overall, there is currently no universally agreed plausible explanation for the differential sex growth outcomes for children under the age of five years. Further research is need unequivocally elucidate the mechanisms explaining sex differences with respect to malnutrition between boys and girls. Such evidence may prove quite beneficial in public health nutrition programming.
The strongest determinant of HAZ in our study was birthweight. Our results confirm results from earlier studies demonstrating the association between birth weight and HAZ among children (26). The positive association between birth weight and height is also evident beyond childhood. A study among Brazilian adolescents demonstrated an increase of 0.28 cm in height corresponding to an increase of 100 g in birth weight (27). Similarly, Jelenkovic, Yokoyama (28) demonstrated birth weight was significantly associated with height from infancy up to adulthood among twins. The mechanisms underlying the association between birth weight and height remain less elucidated. However, it is speculated that intrauterine conditioning may partly explain the associations observed postnatally (29) .
Birth weight was the strongest and only positive determinant of WHZ in our sample. Similar association have previously been reported from nationally representative samples (30). Apart from breastfeeding duration, the other factors negatively associated with WHZ were episode of diarrhea in the last two weeks and maternal age. Our results on diarrhea are in line with findings from other countries from sub-Saharan Africa. Masibo and Makoka (31) and Wasihun, Dejene (32) observed an inverse relationship between diarrhea episode and wasting among Kenyan and Ethiopian children under the age of five respectively. Diarrhea can lead to undernutrition through impaired appetite, malabsorption, acute phase catabolism (33). The negative association between maternal age and WHZ is in contrast with evidence from other studies both in sub-Saharan Africa (34). The difference between our results and those showing a positive association may be due to differential socioeconomic mechanisms operating in different environment (35).
The present study has several of strengths including large sample size, robust statistical approach to account for confounding, effect modification, and mediation. The main weaknesses of the study were failure to control for maternal height, which is a positive predictor of HAZ for children; potential for recall bias for variables measured using maternal memory and cross-sectional design rendering it difficult to ascertain causality. Finally, the effect of residual confounding may not be ruled out. Overall, taken together the present study has demonstrated that breastfeeding duration is negatively associated with growth outcomes among children, however, the effect is unlikely to be of clinical importance.