Fortification of human milk is commonly used to achieve adequate postnatal growth of preterm infants. This can be done using either commercially available human milk fortifiers (HMF) or infant milk powder [1]. Several studies have evaluated the effect of HMF on osmolality of milk, but effect of infant milk powder and other additives has not been adequately studied. Various additives like calcium, iron and multivitamins may increase the osmolality beyond the recommended levels (<450 mOsmol/kg) [2-4]. Increased osmolality of milk has been associated with feed intolerance, delayed gut emptying and necrotizing enterocolitis [3,5,6]. We evaluated the effect of different combinations of fortification and commonly used additives on the osmolality of preterm human milk.

Fortification using milk powder and HMF increased osmolality of EBM, from 303 mOsmol/kg to 397 and 373 mOsmol/kg, respectively. Addition of additives led to a further increase in the osmolality (Fig. 1). The increase in osmolality was largest with addition of 10% calcium gluconate, and least with coconut oil (Fig. 1). Though fortification or additives added alone to unfortified milk did not increase the osmolality beyond 450 mOsml/kg, addition of these additives to fortified milk increased the osmolality beyond this safe limit.

Fig. 1. Osmolality of breast milk with fortification and different combinations of additives.

The increase in osmolality of milk by addition of HMF in our study was comparable to some earlier studies [7,8], but was less than that observed by Kreissl, et al. [9], who also observed marked increase in osmolality by addition of multivitamins, iron and calcium along with HMF.

Addition of additives to fortified milk should be done with caution as this may increase the osmolality of feeds beyond the safe limit. It is important to make paediatricians aware that fortification and additives increase the osmolality of milk which could potentially lead to gut injury in preterm neonates.

Contributors: All authors were involved in the concept, design and analysis of the study. The first draft was prepared by VG and all authors were involved in the revision, and approval of the final version of the manuscript.

Funding: None; Competing interests: None stated.

1. Kuschel CA, Harding JE. Multicomponent fortified human milk for promoting growthin preterm infants. Cochrane Database Syst Rev. 2004;1:CD000343.

2. De Curtis M, Candusso M, Pieltain C, Rigo J. Effect of fortification on the osmolalityof human milk. Arch Dis Child Fetal Neonatal Ed. 1999;81:F141-3.

3. Janjindamai W, Chotsampancharoen T. Effect of fortification on the osmolality ofhuman milk. J Med Assoc Thail Chotmaihet Thangphaet. 2006;89:1400-3.

4. Commentary on breast-feeding and infant formulas, including proposed standards forformulas. Pediatrics. 1976;57:278-85.

5. Pearson F, Johnson MJ, Leaf AA. Milk osmolality: Does it matter? Arch Dis Child Fetal Neonatal Ed. 2013;98:F166-9.

6. Willis DM, Chabot J, Radde IC, Chance GW. Unsuspected hyperosmolality of oralsolutions contributing to necrotizing enterocolitis in very-low-birth-weight infants.Pediatrics. 1977;60:535-8.

7. Agarwal R, Singal A, Aggarwal R, Deorari AK, Paul VK. Effect of fortification withhuman milk fortifier (HMF) and other fortifying agents on the osmolality of pretermbreast milk. Indian Pediatr. 2004;41:63-7.

8. Srinivasan L, Bokiniec R, King C, Weaver G, Edwards AD. Increased osmolality ofbreast milk with therapeutic additives. Arch Dis Child Fetal Neonatal Ed.2004;89:F514-7.