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Effect of Fortifiers and Additional Protein on the Osmolarity of Human Milk: Is It Still Safe for the Premature Infant?

Kreissl, Alexandra*; Zwiauer, Valentina*; Repa, Andreas*; Binder, Christoph*; Haninger, Natalja*; Jilma, Bernd; Berger, Angelika*; Haiden, Nadja*

Journal of Pediatric Gastroenterology and Nutrition: October 2013 - Volume 57 - Issue 4 - p 432–437
doi: 10.1097/MPG.0b013e3182a208c7
Original Articles: Hepatology and Nutrition

Objectives: The present guidelines of the American Academy of Pediatrics recommend that osmolarity not exceed 450 mOsm/kg (or approximately an osmolarity of 400 mOsm/L) for breast milk or infant formulae, to minimize the risk factors for necrotizing enterocolitis. A commercial protein supplement has been developed to meet special protein requirements (4.0–4.5 g · kg−1 · day−1) of infants with a birth weight <1000 g. Because its effect on osmolarity has not been systematically studied, we characterized the effects of fortification on the osmolarity of human milk (HM).

Methods: Osmolarity of fresh and processed HM was measured at baseline, after fortification with a commercial HM fortifier and after further supplementation with additional protein increasing in 0.5-g steps up to 4.0 g. Measurements were performed immediately after adding fortifier and/or protein and after 24 hours. In addition, changes in osmolarity were determined after adding therapeutic additives such as iron, multivitamin supplement, and calcium-phosphorus capsules.

Results: Native HM samples (n = 84) had 297 mOsm/L, (median; 95% confidence interval 295–299 mOsm/L). Adding HM fortifier increased osmolarity up to 436 mOsm/L (95% confidence interval 431–441 mOsm/L). Additional protein supplementation increased osmolarity by 23.5 mOsm/L per 0.5-g step, up to a maximum of 605 mOsm/L. Pasteurization decreased osmolarity by 20–30 mOsm/L (P < 0.001), and storage for 24 hours slightly increased osmolarity (by 11.5 mOsm/L P = 0.0002). Therapeutic additives increased osmolarity up to 868 mOsm/L.

Conclusions: Adding HM fortifier and additional protein to HM increased osmolarity to >400 mOsm/L and therefore above the recommended threshold. Because of the excessive increase in osmolarity combinations of HM + fortifier and additional protein should not be applied together with multivitamins or other additives.

*Department of Pediatrics, Division of Neonatology, Pediatric Intensive Care Medicine and Neuropediatrics

Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.

Address correspondence and reprint requests to Nadja Haiden, MD, Assoc Prof, Department of Pediatrics, Division of Neonatology, Pediatric Intensive Care Medicine and Neuropediatrics, Medical University of Vienna, Waehringer Gürtel 18–20, A-1090 Vienna, Austria (e-mail:

Received 15 February, 2013

Accepted 29 May, 2013

The authors report no conflicts of interest.

© 2013 by European Society for Pediatric Gastroenterology, Hepatology, and Nutrition and North American Society for Pediatric Gastroenterology,