T1D glossary

Dawn phenomenon

Also called dawn effect, morning highs.

The dawn phenomenon is a rise in glucose toward the end of the night, with no low before it and no food. ADA notes that long-acting insulin may not cover a strong dawn phenomenon as well as a pump can. (Huang et al., Somogyi effect study, 2022; ADA Standards of Care 2026, section 9)

Worked example

Glucose sits at 110 mg/dL (6.1 mmol/L) at 3 a.m. and climbs to 160 mg/dL (8.9 mmol/L) by 7 a.m. with no low overnight and nothing eaten: a 50 mg/dL (2.8 mmol/L) rise in the early morning.

Related terms

• Somogyi effect
• Basal insulin
• Closed loop

Sources, quoted

• Huang et al., Somogyi effect study, 2022: “The dawn phenomenon is defined as a spontaneous increase in plasma glucose toward the end of the nocturnal period in the absence of nocturnal hypoglycemia or any intake of dietary carbohydrates.”
• ADA Standards of Care 2026, section 9: “LAAs may not cover strong dawn phenomenon (rise in glucose in early morning hours) as well as pump therapy.”

Every quote above is checked against its source page before each update of this site; last checked 2026-10-06. The worked example is our own arithmetic. This page explains a term; it is not advice for a person's treatment.