Overnight blood glucose levels

When blood glucose levels are constantly out of your target range during the day it can be frustrating. But it is even more concerning when this happens overnight. Firstly, it can interrupt much needed sleep, secondly hypos overnight need to be avoided and lastly, overnight represents a significant portion of the day, so being in target helps your overall average blood glucose value, the HbA1c.

There are many reasons why blood glucose levels could be out of target overnight, including:

  • forgetting your medications or insulin, or taking the wrong dose
  • eating additional carbs at dinner or before bed
  • an incorrect carb count and insulin dose at dinner
  • snacks after dinner without insulin
  • the wrong correction dose of insulin before bed
  • lipohypertrophy
  • drinking more than two glasses of alcohol
  • additional physical activity
  • the ‘dawn phenomenon’

Target range?

It is important you know your blood glucose targets during the day and for overnight. If you are unsure, discuss it with your diabetes team. Make sure you also know what blood glucose target you are aiming for around 2-3am as well. An occasional overnight or morning blood glucose level that is out of target can be expected, but if you notice a pattern of out of target blood glucose levels it needs to be addressed. An unexplained hypoglycaemia event should not occur overnight. If it does it is advised to reduce the insulin dose that works at this time overnight to prevent it happening again.

Insulin dose

If you see a pattern of out of target blood glucose levels occurring then it is time to reflect on why. Is it a cause that can be corrected? If not, your insulin dose(s) may need to be reviewed. It is always best to assess the basal or long acting insulin first, followed by the quick acting insulin if you take it.

The basal insulin should keep the blood glucose steady during the day and overnight, as its role is to match the liver’s secretion of glucose. You can get an idea of what is happening overnight by doing an overnight basal test. You can discuss this with your diabetes team.

When the basal insulin is right for you your blood glucose level should be approximately 2mmol/L higher or lower before breakfast from your bedtime blood glucose level. If the basal insulin falls by more than this your basal insulin dose is too much and will need to be reduced.  If your blood glucose level rises by more than 2mmol/L overnight your basal insulin dose might be too low. However, you should not increase your basal insulin in this case until you have considered the 3am blood glucose result.

If your blood glucose level increased steadily from before bed, 3am and again in the morning, your basal insulin dose is not enough and you need to increase it. If your blood glucose level was stable from before bed until 3am and only increased from 3am to waking then you may have the dawn phenomenon. It is not wise to increase the basal insulin in this circumstance, as it could result in a hypo overnight.

The dawn phenomenon

The dawn phenomenon is a normal rise in blood glucose for some people as their body prepares to wake up. In the early morning hours, hormones such as the growth hormone and cortisol cause the liver to release glucose into the blood. At least having a reason to explain above target blood glucose levels in the morning is helpful; however, it can remain frustrating.

Managing the dawn phenonema is an ongoing research area. For those with type 2 diabetes starting basal insulin is believed to assist in reducing the production of glucose from the liver overnight. If you are already on insulin injections, it is important to consider the 3am blood glucose level before increasing the basal insulin further. For people on an insulin pump, basal rates at that time of day can be increased. Lifestyle changes may also assist. Suggestions include evening exercise, eating less carb and more protein with the evening meal, and not skipping the breakfast meal.

Your diabetes team will be happy to assist you to troubleshoot out of target blood glucose levels.


  1. Porcellati, F et al Thirty Years of Research on the Dawn Phenomenon: Lessons to Optimize Blood Glucose Control in Diabetes. Diabetes Care 2013 36(12) 3860-3862
  2. O’Neal, T, Luther, E. Dawn Phenonema Treasure Island (FL): StatPearls Publishing; 2020 Jan-.



By Helen d’Emden AdvAPD


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