Introduction Appropriate growth of infants is important for their health and further life. In Bangladesh, there are still many infants below the growth standards. Calcium (Ca) is a major component of skeleton and it plays an important role in building bones early in life. The purpose of this study is to investigate the association between Ca level in breast milk and subsequent infants growth in rural Bangladesh.

Methods The MINIMat (“Maternal and Infant Nutrition Interventions in Matlab”) study was initiated by ICDDR,B. This study was nested into the overall MINIMat study. Breast milk samples at 2, 6 and 12 months of postpartum were acquired from 249 women. From obtained breast milk, Ca was measured. Infants' weight and length were attained at 2, 4, 6, 8, 12 and 15 months old and the z-scores were calculated for indicators of infant growth.

Results Around 20%, 15% and 5% of this population was stunting, wasting and underweight. The multivariate regression analyses of Ca in serum and anthropometry indices showed that Ca was significantly associated with weight-for-height z-score (WHZ) and BMI-for-age z-score (BAZ) after adjusting for the effects of parity, wealth index, maternal weight, maternal age, birth weight and sex of the newborn (6 months, WHZ, p=0.001; BAZ, p=0.001; 8 months, WHZ, p=0.001; BAZ, p=0.001). There was not significant relationship between other z-score and Ca in breast milk.

Conclusion This study indicated that Ca level in breast milk might be associated with the underweight at 6 months old in rural Bangladesh.