Deborah O'Connor PhD, RD
Interim Chair
Senior Associate Scientist, Physiology & Experimental Medicine Program, Hospital for Sick Children Scientific Associate Staff, Department of Pediatrics, Division of Neonatology, Mount Sinai Hospital, Sinai Health System
Department of Nutritional Sciences
Deborah O'Connor

Contact Info

T: (416) 978-7235
F: (416) 978-5882


Medical Sciences Building, 5th Floor, Room 5253
1 King's College Circle
Toronto, ON, M5S 1A8


Not accepting new students


PhD, University of Illinois
MS, University of Illinois
Dietetic Internship, Kingston General Hospital
BASc, University of Guelph


Research Synopsis

Our research program is focused on two broad areas of maternal and infant nutrition. First, we are interested in understanding the factors that affect the folate and one-carbon (e.g. vitamin B12) nutrient status of women, infants, and young children. In particular, we are investigating the role folic acid fortification, vitamin and mineral supplementation and colonic bacterial folate biosynthesis play on the folate status of women of reproductive age. Folate and other one carbon nutrients are critically involved in prevention of birth defects and emerging evidence suggests these nutrients also play important roles in epigenetic programming of adult disease.

Second, our research group is actively engaged in supporting human milk feeding of vulnerable infants—specifically the hospitalized infants who have unique nutritional requirements. We have been studying the clinical indications for pasteurized donor human milk when mother’s milk is unavailable and  the impact of feeding nutrient-enriched mother’s own and donor milk  during initial hospitalization and early after hospital discharge on the growth, body composition and development (cognitive and motor) of very low birthweight infants during the first 5 years. With our expert collaborators, we are investigatcoling the role that type of early feeding plays on the gut microbiome of the infants and how this may mediate short- and long-term health outcomes.

Publications and Awards

View PubMed search of this faculty member's recent publications.

Recent Publications

Visentin CE, Masih S, Plumptre L, Schroder TH, Sohn KJ, Ly A, Lausman AY, Berger H, Croxford R, Lamers Y, Kim YI, O’Connor DL. Low maternal serum vitamin B-12 concentrations are prevalent in a cohort of pregnant Canadian women. Journal of Nutrition. 146(5): 1035-42, 2016. (Co-senior responsible author)

Vanderhout SM, Birken CS, Parkin PC, Lebovic G, Chen Y, O’Connor DL, Macguire JL. Higher milk fat content is associated with higher 25-hydroxyvitamin D concentration in early childhood. Applied Physiology Nutrition and Metabolism. 41(5): 516-21, 2016. (Collaborator)

O’Connor DL, Blake J, Bell R, Bowen A, Callum J, Fenton S, Gray-Donald K, Rossiter M, Adamo K, Brett K, Khatri N, Robinson N, Tumback L on behalf of the Society of Obstetricians and Gynecologists of Canada. Canadian Consensus on Female Nutrition: Adolescence, Reproduction, Menopause and Beyond. Journal of Obstetrics and Gynaecology Canada. E-pub ahead of print, 2016.  (First and Senior author)

Panczuk JK, Unger S, Francis J, Bando N, Kiss A, O’Connor DL.  Introduction of bovine-based nutrient fortifier and gastrointestinal inflammation in very low birth weight infants as measured by fecal calprotectin. Breastfeeding Medicine. E-pub ahead of print, Jan-Feb;11:2-5. doi: 10.1089/bfm.2015.0125, 2016. (Senior responsible author)

Kocel S, Russell J, O’Connor DL: Fat-modified breast milk resolves chylous pleural effusion in infants with post-surgical chylothorax but is associated with slow growth. Journal of Parenteral and Enteral Nutrition. 2016 40(4):543-51. (Senior responsible author)

Chan YM, MacFarlane A, MacFarlane A, O’Connor DL. Modelling demonstrates that folic acid fortification of whole wheat flour would reduce the prevalence of folate inadequacy in Canadian whole wheat consumers. Journal of Nutrition. 145(11):2622-2629, 2015. (Senior responsible author)

Plumptre L, Masih S, Ly A, Aufreiter S, Sohn K-J, Croxford R, Lausman AY, Berger H, O’Connor DL, Kim Y-I. High concentrations of folate and unmetabolized folic acid in a cohort of pregnant Canadian women and umbilical cord blood. The American Journal of Clinical Nutrition. 102(4): 848-857, 2015.  (Co-Senior responsible author)

DiLauro S, Unger S, Stone D, O'Connor DL. Breast milk for ill and medically compromised infants: Strategies and ongoing innovation. Journal of Parenteral and Enteral Nutrition. E-Pub ahead of print, February 23, 2016 DOI: 10.1177/0148607116629676 (Co-principal and Senior responsible author)

Masih SP, Plumptre L, Ly A, Berger H, Lausman AY, Croxford R, Kim YI, O’Connor DL. Pregnant Canadian women achieve recommended intakes of one-carbon nutrients through prenatal supplementation but the supplement composition, including choline requires reconsideration. Journal of Nutrition. 145(8):1824-1834, 2015. (Co-Senior responsible author)

Wilson RD; Genetics Committee, Wilson RD, Audibert F, Brock JA, Carroll J, Cartier L, Gagnon A, Johnson JA, Langlois S, Murphy-Kaulbeck L, Okun N, Pastuck M; Special Contributors, Deb-Rinker P, Dodds L, Leon JA, Lowel HL, Luo W, MacFarlane A, McMillan R, Moore A, Mundle W, O'Connor DL, Ray J, Van den Hof M. Pre-conception folic acid and multivitamin supplementation for the primary and secondary prevention of neural tube defects and other folic acid-sensitive congenital anomalies. Journal of Obstetrics and Gynaecology Canada. 2015 Jun;37(6):534-52. (Contributor)

Colapinto CK, O’Connor DL, Sampson M, Williams B, Tremblay MS. Systematic review of adverse health outcomes associated with high serum or red blood cell folate concentrations.  Journal of Public Health. E-pub ahead of print, 2015 38(2):e84-97. (Collaborator)

Visentin CE, Masih S, Plumptre L, Malysheva O, Nielsen DE, Sohn KJ, Lausman AY, Berger H, Croxford R, El-Sohemy A, Caudill MA, O’Connor DL, Kim YI. Maternal choline status, but not fetal genotype, influences cord plasma choline metabolite concentrations. Journal of Nutrition. 145(7):1491-1497, 2015. (Co-Senior responsible author)

Bornstein MH, Putnick DL, Gartstein MA, Hahn C-S, Auestad N, O’Connor DL. Stability of infant temperament by age, gender, birth order, term status, and SES. Child Development. 86(3):844-863, 2015. (Collaborator, Lead Scientist on one of two cohorts of children included in the analyses)

Colapinto C, O’Connor DL, Dubois L, Tremblay M.  Prevalence and correlates of high red blood cell folate concentrations in the Canadian population using three proposed cut-points. Applied Physiology, Nutrition and Metabolism.  40(10):1025-1030, 2015. (Collaborator)

Ng D, Brennan-Donnan J, Unger S, Bando N, Gibbins S, Nash A, Kiss A, O’Connor DL. How close are we to achieving energy and nutrient goals for very low birth weight infants in the first week? Journal of Parenteral and Enteral Nutrition. E-pub ahead of print, 2015 Jul 9. pii: 0148607115594674. (Senior responsible author)

O’Connor DL, Ewaschuk JB and Unger S.  Human milk pasteurization: benefits and risks.  Current Opinion in Clinical Nutrition in Metabolic Care. 18(3):269-275, 2015. (Principal author)

Unger S, Stinzi A, Shah Prakeshkumar, Mack D, O’Connor DL: The Gut Microbiota of the Very Low Birth Weight Infant. Pediatric Research. 77(1-2):205-213, 2015. (Senior responsible author)

Shere M, Nguyen P, Tam C, Stern S, Kapur B, O'Connor DL, Koren G: Pregnancy-induced changes in the long-term pharmacokinetics of 1.1 mg vs. 5 mg folic acid: A randomized clinical trial. Journal of Clinical Pharmacology. 55(2):159-167, 2015. (Collaborator)

Colapinto CK, Tremblay MS, Aufreiter S, Bushnik T, Pfeiffer CM, O’Connor DL:  The direction of the difference between Canadian and American red blood cell folate concentrations is dependent on the assay method employed: A comparison of the Canadian Health Measures Survey and National Health and Nutrition Examination Survey. British Journal of Nutrition. 112(11):1873-1881, 2014. (Co-senior responsible author)

Lakoff A, Fazili Z, Aufreiter S, Pfeiffer CM, Connolly B, Gregory III JF, Pencharz PB, O’Connor DL: Folate is absorbed across the human colon: evidence using enteric coated caplets containing 13C-labeled [6S]-5-formyltetrahydrofolate. The American Journal of Clinical Nutrition. 100(5):1278-1286, 2014. (Senior responsible author)

Fayyaz F, Wang F, Jacobs RL, O’Connor DL, Bell RC, Field CJ. Folate, vitamin B12 and vitamin B6 status of a group of high socio-economic status women in the Alberta Pregnancy Outcomes and Nutrition (APrON) cohort. Applied Physiology, Nutrition and Metabolism. 39(12):1402-1408, 2014. (Collaborator)

Hartman B, Fazili Z, Pfeiffer CM, O’Connor DL: Neither  folic acid supplementation nor pregnancy affect the distribution of folate forms in the red blood cells of women. Journal of Nutrition. 144(9):1364-1369, 2014. (Senior responsible author)

Kasierer Y, O’Connor DL, Rutherford E, Rolnitsky A, Unger S: Implications for Orthodox Jewish families in the provision of mother’s own and donor milk for their very low birth weight infant. Journal of Human Lactation. 30(4):402-404, 2014. (Co-author)        
Unger S, Gibbins S, Zupancic J, O’Connor DL:  DoMINO: Donor milk for improved neurodevelopmental outcomes (Study Protocol). BMC Pediatrics. 14:123, 2014.  (Senior responsible author)

Panczuk J, Unger S, O’Connor D, Lee SL:   Human donor milk for the vulnerable infant:  a Canadian perspective.  International Breastfeeding Journal. 9:4, 2014. (Co-author)

Ley SH, Hanley AJ, Sermer M, Zinman B, O’Connor DL:  Lower dietary vitamin E intake during the second trimester is associated with insulin resistance and hyperglycemia later in pregnancy. European Journal of Clinical Nutrition. 67(11): 1154-1156, 2013. (Co-senior responsible author)

Gibbins S, Wong S, Unger S, O’Connor DL.  Donor human milk for preterm infants: practice considerations. Journal of Neonatal Nursing. 19(4):175-181, 2013. (Senior responsible author).
Lapillonne A, O’Connor DL, Wang D, Rigo J. Nutritional recommendations for the late-preterm infant and the preterm infant after hospital discharge. Journal of Pediatrics. 162(Supplement 3):S90-100, 2013. (Co-author)

Colapinto CK, O’Connor DL, Dubois L, Tremblay MS. Prevalence and correlates of folic acid supplement use in Canada.  Health Reports. 23(2):39-44, 2012. (Co-senior responsible author) 
Pichardo D, Luginbuehl IA, Shakur Y, Wales P, El-Sohemy A, O’Connor DL. Effect of nitrous oxide exposure during surgery on homocysteine concentrations of children.  Anesthesiology. 117(1):15-21, 2012. (Senior responsible author)

Colapinto CK, O’Connor DL, Dubois L, Tremblay MS.  Folic acid supplement use is the most significant predictor of folate concentrations in Canadian women of childbearing age.  Applied Physiology, Nutrition and Metabolism. 37(2):284-292, 2012.  (Co-senior responsible author)

Ley SH, Hanley AJ, Sermer M, Zinman B, O’Connor DL. Association of prenatal metabolic abnormalities with insulin and adiponectin concentrations in human milk.  American Journal of Clinical Nutrition. 95(4):867-874, 2012. (Co-senior responsible author)

Shakur YA, Tarasuk V, Corey P, O’Connor DL. A comparison of the micronutrient inadequacy and risk of high micronutrient intakes among vitamin and mineral supplement users and non-users in Canada. Journal of Nutrition. 142(3):534-540, 2012. (Senior responsible author)

O’Connor DL, Weishuhn K, Rovet J, Mirabella G, Jefferies A, Campbell DM, Asztalos E, Feldman M, Whyte H, Westall C on behalf of the Post-Discharge Feeding Study Group. Visual development of human milk–fed preterm infants provided with extra energy and nutrients after hospital discharge. Journal of Parenteral and Enteral Nutrition. 36(3):349-353, 2012. (Principal author)

Tam C, O’Connor DL, Koren G. Circulating unmetabolized folic acid: relationship to folate status and effect of supplementation. Obstetrics and Gynecology International. 2012:485179, 2012. (Collaborator)

Ley SH, Hanley AJ, Retnakaran R, Sermer M, Zinman B, O’Connor DL. Effect of macronutrient intake during the second trimester on glucose metabolism later in pregnancy. American Journal of Clinical Nutrition. 94(5):1232-1240, 2011.  (Co-senior responsible author)

Nash A, Dunn M, Asztalos E, Corey M, Mulvihill-Jory B, O’Connor DL:  Pattern of growth of very low birth weight preterm infants, assessed using the WHO Growth Standards, is associated with neurodevelopment. Applied Physiology, Nutrition and Metabolism. 36(4):562-569, 2011.  (Senior responsible author)

Ley S, MSc, Hanley AJ, Stone D, O'Connor DL:  Effects of pasteurization on adiponectin and insulin concentrations in donor human milk. Pediatric Research. Sep;70(3):278-281, 2011. (Co-senior responsible author)

Weinmann A, Post M, Pan J, Rafi M, O'Connor DL, Unger S, Pencharz P, Belik J. Tetrahydrobiopterin is present in high quantity in human milk and has a vasorelaxing effect on newborn rat mesenteric arteries. Pediatric Research. Apr;69(4):325-329, 2011. (Collaborator)

Ewaschuk JB, Unger S, Harvey S, O’Connor DL, Field CJ. Effect of pasteurization on immune components of milk: implications for feeding preterm infants. Applied Physiology, Nutrition, and Metabolism. 36(2):175-182, 2011. (Co-investigator)

Ewaschuk JB, Unger S, O’Connor DL, Stone D, Harvey S, Clandinin MT, Field CJ. Effect of pasteurization on selected immune components of donated human milk.  J Perinatology. Sep;31(9):593-598, 2011.  (Co-investigator)

Aufreiter S, Kim JH, O’Connor DL. Dietary oligosaccharides increase colonic weight and the amount but not concentration of bacterially synthesized folate in the colon of piglets. Journal of Nutrition. 141(3):366-372, 2011. (Senior responsible author)

Grant SM, Wolever TMS, O'Connor DL, Nisenbaum R, Josse JG:  Effect of a low glycaemic index diet on blood glucose in women with gestational hyperglycaemia.  Diabetes Research and Clinical Practice. Jan; 91(1):15-22, 2011. (Collaborator)

Maguire JL, Birken CS, O’Connor DL, Mamdani M, Macarthur C, Thorpe KE. Prevalence and predictors of low vitamin D in urban Canadian toddlers. Pediatrics & Child Health. 16(2): e11-e15, 2011. (Collaborator)

Ley SH, O'Connor DL, Retnakaran R, Hamilton JK, Sermer M, Zinman B, Hanley AJ.  Impact of maternal metabolic abnormalities in pregnancy on human milk and subsequent infant metabolic development: methodology and design. BMC Public Health. 10(1):590, 2010.  (Co-senior responsible author)

Shakur Y, Garriguet D, Corey P and O’Connor DL. Folic acid fortification over mandated levels results in a low prevalence of folate inadequacy among Canadians. American Journal of Clinical Nutrition. 92(4):818-825, 2010. (Senior responsible author)

Colapinto C, O’Connor DL, Tremblay M. Folate status of the population in the Canadian Health Measures.  Canadian Medical Association Journal. 183(2):E100-106, 2011. (Co-senior responsible author)                                     

Non-Refereed Book Chapters and Reviews:      

O’Connor DL, Unger S. Post-discharge nutrition of the breastfed preterm infant. Seminars in Fetal and Neonatal Medicine 18(3) 124-128, 2013., (Principal author).

Chan YM, Bailey R, O’Connor DL: Folate. Advances in Nutrition 4(1):123-5, 2013. (Senior responsible author)

O’Connor DL, Picciano MF:  Lactation.  In:  Modern Nutrition in Health and Disease, edited by Ross AC,  Caballero B, Cousins R, Tucker KL, Ziegler TR. Lippincott Williams & Wilkins, Chapter 53,  pg 698-771, 2013. (Principal author)

Honours and Awards

2015 Khursheed Jeejeebhoy Award, Canadian Nutrition Society
2000 Pinnacle Award of Excellence, Ross Products Division, Abbott Laboratories
1998 Chairman’s Award, Abbott Laboratories
1997 Alumni Medal of Achievement, University of Guelph Alumni Association
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