Sleep Guide, Part 3 of 4
The 4am Rise
Why your morning glucose is higher than your overnight low. The growth-hormone surge, the dawn phenomenon, what counted as a 1.4 mmol/L (25 mg/dL) rise versus a 3.3 mmol/L (60 mg/dL) rise across the analogue-insulin generations. What an overnight basal review looks like with your team. What the AID overnight target lever does and does not do.
Ask Grace
Want to dig into the dawn-phenomenon mechanism, the AID overnight-target lever, or your own basal pattern? Ask Grace.
Why your morning glucose is higher than your overnight low
You go to bed at 6.5 mmol/L (117 mg/dL). You wake at 4am to a CGM line that has drifted up to 8.0 mmol/L (144 mg/dL), with no food, no correction, no obvious explanation. By 7am it is at 9.5 mmol/L (171 mg/dL), and the pre-breakfast bolus has more work to do than yesterday’s. From the conversations I have in DAFNE and BERTIE, and from the same conversation at home with my own daughter, this is the moment people most often blame on themselves: the late-evening snack, the basal that “must be wrong”, the discipline that “must have slipped”. It is rarely any of those things. The body is doing exactly what bodies do at dawn. The morning rise is not a personal failing.
The mechanism, in plain terms
The dawn phenomenon was first described by Schmidt and colleagues in 1981 as a night-to-morning rise in blood glucose without any food intake. Bolli and Gerich confirmed in 1984 that the same phenomenon occurred in both T1D and T2D, driven primarily by nocturnal growth-hormone pulses around 03:00 to 06:00 that accelerate hepatic glucose production and reduce peripheral insulin sensitivity (Porcellati and colleagues, 2013, Diabetes Care 30-year review). The healthy non-diabetic body pre-empts this with a small anticipatory insulin pulse just before dawn. T1D, by definition, cannot do that. T2D, in the early stages, can do less of it. The visible rise is the gap between what the body needs and what insulin replacement, on its current settings, can deliver.
How big is the rise, really
The size of that gap depends largely on overnight insulin. With older NPH or lente insulins that wane overnight, the apparent dawn rise can look like 3 to 5 mmol/L (50 to 100 mg/dL). With continuous subcutaneous insulin infusion at a single basal rate, or with the modern long-acting analogues (glargine U100, glargine U300, degludec), the true T1D dawn-phenomenon magnitude settles at around 1.4 to 1.7 mmol/L (25 to 30 mg/dL) pre-breakfast, rising to around 2.8 to 3.3 mmol/L (50 to 60 mg/dL) post-breakfast (Porcellati 2013, Diabetes Care). At the population scale, in non-insulin-treated T2D, the dawn phenomenon contributes around 0.4 percentage points to HbA1c on its own, and no oral antidiabetes agent in current use eliminates it.
The lever that moves it
The lever that most consistently moves the dawn rise is overnight insulin programming. On multiple daily injections, that conversation is about the timing and dose of basal insulin (often glargine U300 or degludec). On pump therapy, that conversation is about the overnight basal-rate profile: many people benefit from a programmed basal-rate increase running roughly 03:00 to 06:00. On automated insulin delivery, the system is doing this work every night, and many people benefit from a tighter overnight target. The MiniMed 780G AHCL pivotal trial ran a randomised within-person crossover between a 5.5 mmol/L (100 mg/dL) target and a 6.7 mmol/L (120 mg/dL) target across roughly 90 days each; the lower target produced higher time-in-range, with a modest rise in time below 3.9 mmol/L (Carlson 2022, Diabetes Technology and Therapeutics). Overnight target tightening is the AID lever this finding maps onto.
Any specific dose change is a clinical decision your team makes with you. The numeric figures referenced here are population-average estimates at typical total daily doses. People living with T1D have their own correction factors set with their diabetes care team, and those personal factors drive any individual change. GNL does not recommend a specific overnight dose adjustment; the role of this guide is to put the dawn phenomenon into context so the conversation at the next clinic appointment can be specific.
Take the morning rise to your team
If your morning glucose is consistently higher than your overnight low, that is a pattern worth bringing to your team rather than carrying alone. Your diabetes care team is the first conversation. Ask whether an overnight basal review is appropriate, whether an AID overnight target adjustment is on the table if you are on AID, and whether the long-acting analogue you are using is the best fit for your overnight pattern.
Part 3 of 4
The 4am Rise