Professor  |  Earle W. McHenry Professor, and Chair I Canada Research Chair in Human Milk and Infant Nutrition

Deborah O'Connor

Department of Nutritional Sciences


Medical Sciences Building
1 King's College Circle, Toronto, Ontario Canada M5S 1A8
Research Interests
human milk composition, impact of diet on colonic folate biosynthesis and absorption, nutrient fortification of human milk for hospitalized infants, nutrition during pregnancy and lactation , promotion of human milk feeding in vulnerable populations, very low birth weight infants
Appointment Status
Not accepting new students


  • 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)

Canadian Nutrition Society Fellow (2023)

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. Asbury MR, Shama S, Sa JY, Bando N, Butcher J, Comelli EM, Copeland JK, Forte V, Kiss A, Sherman PM, Stintzi A, Taibi A, Tomlinson C, Unger S, Wang PW, O'Connor DL; OptiMoM Feeding Group. Human milk nutrient fortifiers alter the developing gastrointestinal microbiota of very-low-birth-weight infants. Cell Host Microbe. 2022 Aug 12:S1931-3128(22)00357-2. doi: 10.1016/j.chom.2022.07.011. Epub ahead of print. PMID: 35987195.
  2. Xu J, Shin J, McGee M, Unger S, Bando N, Sato J, Vandewouw M, Patel Y, Branson HM, Paus T, Pausova Z, O'Connor DL. Intake of mother's milk by very low birth weight infants and variation in DNA methylation of genes involved in neurodevelopment at 5.5 years. Am J Clin Nutr. 2022 Aug 17:nqac221. doi: 10.1093/ajcn/nqac221. Epub ahead of print. PMID: 35977396.
  3. Sato J, McGee M, Bando N, Law N, Unger S, O'Connor DL. Diet Quality and Cognitive Performance in Children Born Very Low Birth Weight. Front Nutr. 2022 Jul 19;9:874118. doi: 10.3389/fnut.2022.874118. PMID: 35928843; PMCID: PMC9343771.
  4. Wilson RD, O'Connor DL. Guideline No. 427: Folic Acid and Multivitamin Supplementation for Prevention of Folic Acid-Sensitive Congenital Anomalies. J Obstet Gynaecol Can. 2022 Jun;44(6):707-719.e1. doi: 10.1016/j.jogc.2022.04.004. PMID: 35691683.
  5. Mildon A, Francis J, Stewart S, Underhill B, Ng YM, Rousseau C, Di Ruggiero E, Dennis CL, Kiss A, O'Connor DL, Sellen DW. Associations between use of expressed human milk at 2 weeks postpartum and human milk feeding practices to 6 months: a prospective cohort study with vulnerable women in Toronto, Canada. BMJ Open. 2022 Jun 8;12(6):e055830. doi: 10.1136/bmjopen-2021-055830. PMID: 35676013; PMCID: PMC9185489.
  6. Kothari A, Pitino MA, Unger S, Perreault V, Doyen A, Pouliot Y, McGeer AJ, Stone D, O'Connor DL. Preservation of Anti-cytomegalovirus Activity in Human Milk Following High-Pressure Processing Compared to Holder Pasteurization. Front Nutr. 2022 May 19;9:918814. doi: 10.3389/fnut.2022.918814. PMID: 35662924; PMCID: PMC9160983.
  7. Sato J, Vandewouw MM, Safar K, Ng DVY, Bando N, O'Connor DL, Unger SL, Pang E, Taylor MJ. Social-Cognitive Network Connectivity in Preterm Children and Relations With Early Nutrition and Developmental Outcomes. Front Syst Neurosci. 2022 Apr 7;16:812111. doi: 10.3389/fnsys.2022.812111. PMID: 35465192; PMCID: PMC9022474.
  8. Mullen AJ, O'Connor DL, Hanley AJ, Piedimonte G, Wallace M, Ley SH. Associations of Metabolic and Obstetric Risk Parameters with Timing of Lactogenesis II. Nutrients. 2022 Feb 19;14(4):876. doi: 10.3390/nu14040876. PMID: 35215526; PMCID: PMC8879345.
  9. Walton K, McGee M, Sato J, Law N, Hopperton KE, Bando N, Kiss A, Unger S, O'Connor DL. Social-Emotional Functioning and Dietary Intake among Children Born with a Very Low Birth Weight. Appl Physiol Nutr Metab. 2022 Feb 23. doi: 10.1139/apnm-2021-0434. Epub ahead of print. PMID: 35196153.
  10. Hopperton KE, Pitino MA, Walton K, Kiss A, Unger SL, O'Connor DL, Bazinet RP. Docosahexaenoic acid and arachidonic acid levels are correlated in human milk: Implications for new European infant formula regulations. Lipids. 2022 Feb 15. doi: 10.1002/lipd.12338. Epub ahead of print. PMID: 35170053.

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