Professor  |  Earle W. McHenry Professor, and Chair

Deborah O'Connor

Department of Nutritional Sciences


Medical Sciences Building, 5th Floor, Room 5253
1 King's College Circle, Toronto, Ontario Canada M5S 1A8
Research Interests
promotion of human milk feeding in vulnerable populations, nutrient fortification of human milk for hospitalized infants, very low birth weight infants, human milk composition, nutrition during pregnancy and lactation , impact of diet on colonic folate biosynthesis and absorption
Appointment Status
Pending the availability of funding


  • PhD, Nutritional Sciences, University of Illinois (1989)
  • MS, Nutritional Sciences, University of Illinois (1986)
  • RD, Clinical Dietetic Internship, Kingston General Hospital (1984)
  • BASc, Applied Human Nutrition, University of Guelph (1983)

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Other Academic Appointments

Scientific Associate Staff, Department of Pediatrics, Division of Neonatology, Mount Sinai Hospital, Sinai Health System (2016 – present)

Senior Associate Scientist—Status Only, Research Institute, Translational Medicine Program, The Hospital for Sick Children (2013 – present)

At a Glance

  • Dr. O’Connor is a recognized authority in human milk and infant nutrition and is frequently asked for her expert opinion in preparing national and international maternal and neonatal nutrition guidelines. Her research team examines strategies to increase the use of human milk in vulnerable populations which includes use of donor human milk when parent milk is unavailable.
  • Dr. O'Connor is also 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, her work investigates the role folic acid fortification, vitamin and mineral supplementation and colonic bacterial folate biosynthesis play on the folate status of women of reproductive age.

About Dr. Deborah O'Connor

Dr. Deborah (Debbie) O’Connor is the Earle W. McHenry Professor and Chair of the Department of Nutritional Sciences at the University of Toronto. She also holds scientific appointments in the Translational Medicine Program at the Hospital for Sick Children and the Department of Pediatrics at Mount Sinai Hospital. At SickKids, she served as Director of Clinical Dietetics and Breastfeeding Support from 2000 to 2012 and then as Associate Chief of Academic and Professional Practice until 2013. She currently serves as Chair of the Advisory Board for the Rogers Hixon Ontario Human Milk Bank located at Mount Sinai Hospital.

Dr. O’Connor has served on national and international committees and working groups, including the Society of Obstetricians and Gynecologists of Canada Nutrition Practice Guidelines, US-Canada Governments Joint Dietary Reference Intake Working Group on Chronic Disease Endpoints, US National Academy of Sciences, Engineering and Medicine Exploration of New Evidence for Nutrition During Pregnancy and Lactation, and the World Health Organization on technical aspects of human milk banking and use of powdered formulas.

Research Synopsis

Dr. O’Connor’s research program broadly is in the area of human milk and infant nutrition. Specifically, her team is actively engaged in evaluating strategies to support human milk feeding of vulnerable infants whether infants are hospitalized very low birth weight infants with elevated nutritional requirements or term-born infants with unique medical conditions requiring lacto-engineered human milk such as in post-surgical chylothorax in infants where lymph fluid accumulates in the chest cavity. More recently she expanded her research out of the clinical setting to community centres to explore strategies to support human milk feeding in socially and economically vulnerable women that represent a large portion of her research participants. Outcomes of interest in her early feeding interventions include normal growth, neurodevelopment, gut colonization and a reduction in morbidity.  Mediating factors include the impact of maternal diet and antibiotic use on milk nutrient and bioactive component composition.

Second, Dr. O’Connor’s is interested in understanding the factors that affect the folate and other one-carbon (e.g. vitamin B12) nutrient status of women, infants, and young children. In particular, she is interested in investigating what roles universal folic acid fortification of the food supply, 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.

Research conducted by Dr. O’Connor and her team is funded by CIHR, NSERC, the Sprott Foundation, and the Lawson Centre for Child Nutrition.

Recent Awards and Distinctions (Selected)

Earle W. McHenry Award for Distinguished Service in Nutrition, Canadian Nutrition Society (2020)

Earle W. McHenry Chair, University of Toronto (2020)

Faith Elizabeth Winifred (Rusted) Bayley Nutrition Lectureship, Memorial University (2016)

Khursheed Jeejeebhoy Award, Canadian Nutrition Society (2015)

National and International Committee Memberships (Current)

Work Group Member, Breastmilk Ecology – Genesis in Infant Nutrition (BEGIN), Eunice Kennedy Shriver, National Institutes of Health and Human Development (2020 – present)

Scientific Expert, Human Milk Composition Initiative, US-Canada Governments (2019 – present)

Recent Publications

  1. Francis J, Ismail S, Mildon A, Stewart S, Underhill B, Tarasuk V, Di Ruggiero E, Kiss A, Sellen DW, O'Connor DL. Characteristics of vulnerable women and their association with participation in a Canada Prenatal Nutrition Program site in Toronto, Canada. Health Promot Chronic Dis Prev Can. 2021 Dec;41(12):413-422. English, French. doi: 10.24095/hpcdp.41.12.02. PMID: 34910898.
  2. Tyebally Fang M, Chatzixiros E, Grummer-Strawn L, Engmann C, Israel-Ballard K, Mansen K, O'Connor DL, Unger S, Herson M, Weaver G, Biller-Andorno N. Developing global guidance on human milk banking. Bull World Health Organ. 2021 Dec 1;99(12):892-900. doi: 10.2471/BLT.21.286943. Epub 2021 Oct 20. PMID: 34866685; PMCID: PMC8640695.
  3. O'Connor DL. Breastfeeding: when will enough evidence be enough? Am J Clin Nutr. 2021 Nov 8;114(5):1577-1578. doi: 10.1093/ajcn/nqab252. PMID: 34637501.
  4. Sato J, Vandewouw MM, Bando N, Branson HM, O'Connor DL, Unger SL, Taylor MJ. White matter alterations and cognitive outcomes in children born very low birth weight. Neuroimage Clin. 2021;32:102843. doi: 10.1016/j.nicl.2021.102843. Epub 2021 Sep 28. PMID: 34601309; PMCID: PMC8496319.
  5. LeMay-Nedjelski L, Yonemitsu C, Asbury MR, Butcher J, Ley SH, Hanley AJ, Kiss A, Unger S, Copeland JK, Wang PW, Stintzi A, Bode L, O'Connor DL. Oligosaccharides and Microbiota in Human Milk Are Interrelated at 3 Months Postpartum in a Cohort of Women with a High Prevalence of Gestational Impaired Glucose Tolerance. J Nutr. 2021 Nov 2;151(11):3431-3441. doi: 10.1093/jn/nxab270. PMID: 34510198; PMCID: PMC8562078.
  6. D'Hollander CJ, Keown-Stoneman CDG, Birken CS, O'Connor DL, Maguire JL; TARGet Kids! collaboration. Timing of Introduction to Solid Food, Growth, and Nutrition Risk in Later Childhood. J Pediatr. 2022 Jan;240:102-109.e3. doi: 10.1016/j.jpeds.2021.08.076. Epub 2021 Sep 2. PMID: 34481809.
  7. Vanderhout SM, Keown-Stoneman CDG, Birken CS, O'Connor DL, Thorpe KE, Maguire JL. Cow's milk fat and child adiposity: a prospective cohort study. Int J Obes (Lond). 2021 Dec;45(12):2623-2628. doi: 10.1038/s41366-021-00948-6. Epub 2021 Aug 25. PMID: 34433906.
  8. Mildon A, Francis J, Stewart S, Underhill B, Ng YM, Rousseau C, Di Ruggiero E, Dennis CL, O'Connor DL, Sellen DW. High levels of breastmilk feeding despite a low rate of exclusive breastfeeding for 6 months in a cohort of vulnerable women in Toronto, Canada. Matern Child Nutr. 2022 Jan;18(1):e13260. doi: 10.1111/mcn.13260. Epub 2021 Aug 8. PMID: 34369075; PMCID: PMC8710126.
  9. Hopperton KE, Pitino MA, Chouinard-Watkins R, Shama S, Sammut N, Bando N, Williams BA, Walton K, Kiss A, Unger SL, Bazinet RP, O'Connor DL. Determinants of fatty acid content and composition of human milk fed to infants born weighing <1250 g. Am J Clin Nutr. 2021 Oct 4;114(4):1523-1534. doi: 10.1093/ajcn/nqab222. PMID: 34254983; PMCID: PMC8488876.
  10. Mildon A, Francis J, Stewart S, Underhill B, Ng YM, Richards E, Rousseau C, Di Ruggiero E, Dennis CL, O'Connor DL, Sellen DW. Effect on breastfeeding practices of providing in-home lactation support to vulnerable women through the Canada Prenatal Nutrition Program: protocol for a pre/post intervention study. Int Breastfeed J. 2021 Jul 2;16(1):49. doi: 10.1186/s13006-021-00396-y. Erratum in: Int Breastfeed J. 2021 Jul 29;16(1):57. PMID: 34215288; PMCID: PMC8252273.

In the News

Hard pill to swallow – the truth behind multivitamins. The Varsity (U of T). October 25, 2020.

Breast milk microbiota in mothers of preterm infants affected by antibiotics. Genetic Engineering & Biotechnology News. September 8, 2020.

From Canada to Uganda and beyond: U of T researchers receive funding for COVID-19 projects. July 21, 2020.

Pasteurizing breast milk inactivates SARS-CoV-2 virus, U of T study shows. U of T News. July 13, 2020.

Current Lab Members

Dr. Jo-Anna Baxter – Postdoctoral Fellow

Dr. Megan Beggs – Postdoctoral Fellow

Dr. Kathryn Walton – Postdoctoral Fellow

Dr. Amelia Jingxiong Xu – Postdoctoral Fellow

Michelle Asbury – PhD student

Nicole Bando – PhD student

Alison Mildon (co-supervisor) – PhD student

Michael Pitino – PhD student

Sara Shama – PhD student

Victoria Colaluca – MSc student

Adrianna Greco – MSc student

Samantha Ismail – MSc student