There are several studies.  The newest article is:
 
An Exclusively Human Milk-Based Diet Is Associated with a  Lower Rate of 
Necrotizing Enterocolitis than a Diet of Human Milk and Bovine Milk-Based 
Products , 28 December 2009 
Sandra Sullivan,  Richard J. Schanler, Jae H. Kim, Aloka L. Patel, Rudolf 
Trawöger, Ursula  Kiechl-Kohlendorfer, Gary M. Chan, Cynthia L. Blanco, 
Steven Abrams, C. Michael  Cotton, Nirupama Laroia, Richard A. Ehrenkranz, Golde 
Dudell, Elizabeth A.  Cristofalo, Paula Meier, Martin L. Lee, David J. 
Rechtman, Alan Lucas 
The Journal of Pediatrics 
April 2010 (Vol. 156,  Issue 4, Pages 562-567.e1)
_Abstract_ (http://www.jpeds.com/search/quick#)  | _Full Text_ 
(http://www.jpeds.com/search/quick#)  | _Full-Text PDF (197 KB)_ 
(http://download.journals.elsevierhealth.com/pdfs/journals/0022-3476/PIIS0022347609010853.pdf)  
 
For the rest, read Chapter 7 of "Best Medicine: Human Milk in the NICU" by  
Wight, Morton and Kim, available from Hale Publishing, July 2008.
 
Nancy
Nancy E. Wight MD, IBCLC, FABM,  FAAP
Neonatologist
Sharp Mary Birch Hospital for Women and  Newborns
Medical Director, Sharp HealthCare Lactation Services
San Diego,  CA 
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