Canadian Study: Breastfeeding Blood Sugar Patterns in Type 1 Diabetes

A study from Canada offers important new insights for new mothers managing Type 1 diabetes while breastfeeding — a combination that has long raised concerns about dangerous nighttime blood sugar drops. Researchers at the University of Calgary's Cumming School of Medicine tracked blood sugar patterns in 18 women with Type 1 diabetes during the first six months after delivery, with findings published in the prestigious journal Diabetologia in 2024.

What the Canadian Researchers Found

Using continuous glucose monitoring (CGM), the research team analyzed blood sugar readings during the three hours following breastfeeding sessions. The reassuring headline finding: blood sugar remained above 70 mg/dL (3.9 mmol/L) — the clinical threshold for hypoglycemia — in 93% of all breastfeeding episodes. However, nighttime feedings did produce a measurable average glucose drop of approximately 20 mg/dL per hour (1.1 mmol/L per hour) in the three hours following nursing.

The study's most clinically significant finding involved a comparison between two insulin delivery systems:

• Open-loop therapy (sensor-augmented insulin pump, manually adjusted): Nighttime glucose dropped an average of 21.6 mg/dL (1.2 mmol/L) after breastfeeding.
• Closed-loop therapy (automated insulin delivery, or "artificial pancreas"): Nighttime glucose dropped only 7.2 mg/dL (0.4 mmol/L) — a significantly blunted response (p<0.01).

This suggests that closed-loop systems, which automatically adjust insulin based on real-time CGM data, may be actively compensating for the glucose-lowering effect of breastfeeding — offering an additional layer of nighttime safety.

Why an International Perspective Matters

Canada's universal healthcare system allows researchers to study insulin delivery technologies in real-world postpartum settings with fewer access barriers than in the US. Canadian diabetes care guidelines closely mirror American Diabetes Association (ADA) standards, making this data highly applicable to US patients. Additionally, closed-loop insulin systems studied here — including devices like the Tandem Control-IQ and Omnipod 5 — are now FDA-approved and increasingly available to American mothers with Type 1 diabetes.

How This Compares to US Guidelines

Current ADA guidelines acknowledge that breastfeeding can lower blood glucose in women with Type 1 diabetes and recommend extra carbohydrate intake and vigilant CGM use during nursing. However, specific guidance on closed-loop system use in postpartum breastfeeding women remains limited. This Canadian research helps fill that gap with real-world clinical evidence.

Why This Matters for US Patients

For the estimated 1.6 million American women living with Type 1 diabetes of childbearing age, nighttime hypoglycemia during breastfeeding is a genuine safety concern — both for the mother and for infant care responsibilities. This study provides evidence-based reassurance that severe hypoglycemia after breastfeeding is uncommon, while also suggesting that closed-loop insulin delivery systems may provide meaningful additional protection during those vulnerable overnight hours. American mothers currently using or considering an automated insulin delivery system should discuss these findings with their endocrinologist, particularly when planning postpartum diabetes management.

Study Citation

Donovan, Bell, & Feig. "Glycaemic patterns during breastfeeding with postpartum use of closed-loop insulin delivery in women with type 1 diabetes." Diabetologia (2024). PMID: 39028360. DOI: 10.1007/s00125-024-06227-z