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The dawn phenomenon: Why does blood sugar spike in the morning?

Have you woken up with elevated blood sugar levels? Not to fear, we're here to explain the dawn phenomenon.
Napala Pratini
12/7/2021
5
min read
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Quick summary

  • Blood glucose levels can rise overnight and show up as elevated sugar levels in the morning—a phenomenon called dawn syndrome.
  • Dawn syndrome isn't anything to worry about, as it's a natural hormonal response.
  • That said, there are some things you can do to minimise morning sugar spikes and keep blood sugar levels in a healthy range.

If you have type 2 diabetes and practice self-monitoring of blood glucose levels, you may have noticed that you frequently wake up in the morning with high blood sugar levels. You are likely experiencing the dawn phenomenon.

Learn what this natural phenomenon is, why it occurs, why you may be experiencing it, and how to treat morning sugar spikes.

What is the dawn phenomenon?

The dawn phenomenon is a term used to describe hyperglycemia – high blood sugar levels – in the early hours of the morning.

This spike occurs between the hours of 3 a.m. and 8 a.m. and occurs in everyone (not just people with diabetes), to a degree. Most people do not notice this natural shift in blood sugar levels.

However, it is more commonly seen in individuals with diabetes, occurring in over 50% of diabetics.[1]

Not only is the incidence of the dawn phenomenon higher in those with diabetes, but blood sugar levels tend to rise to much higher levels than those without the disease. As most people with diabetes are well aware of, elevated blood sugar levels are unhealthy and can lead to many harmful complications.  

Why do blood sugar spikes occur in the morning?

While the exact mechanism behind the dawn phenomenon is not fully known, researchers think that blood sugar can spike in the morning due to natural shifts in hormones that occur during the night as you sleep.

Hormones your body releases while you sleep include growth hormone, cortisol, glucagon, and more… all of which stimulate an increase in blood sugar levels to get us ready for the day ahead. These hormones work by both increasing the amounts of stored sugar released into the blood as well as decreased blood sugar uptake by cells. The body also appears to be more insulin resistant in the early morning, making the effect of these hormones even greater.[2]

The body is slightly more insulin resistant in the morning, making the impact of blood glucose raising hormones even more significant.

Chanoine et al, Journal of Clinical Endocrinology and Metabolism

Another related but different phenomenon is referred to as the Somogyi effect, which also results in morning blood sugar spikes. The difference is that the Somogyi effect is thought to be in response to hypoglycaemia – but researchers are still debating whether this actually happens as new data is seeming to suggest that blood sugar is actually elevated overnight.

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How to know if you're experiencing the dawn phenomenon

The most reliable avenue for checking to see if you are experiencing dawn phenomenon is to test and track your blood sugar levels during the hours of 3 a.m. and 8 a.m… or, if you don’t fancy waking up in the middle of the night, first thing when you wake up.

Other indicators of the dawn phenomenon are simply the symptoms of high blood sugar, including: 

  • Faintness
  • Nausea
  • Vomiting
  • Blurry vision
  • Weakness
  • Disorientation
  • Feeling tired
  • Extreme thirst

Management of hyperglycaemia is important, as potential long-term complications can include:

  • Cardiovascular problems
  • Nerve damage, in some cases leading to limb amputation
  • Vision complications and/or loss
  • Organ damage

What is the treatment for dawn phenomenon? 

If you are experiencing dawn phenomenon, seek guidance from your practitioner, endocrinologist, or certified diabetic educator, particularly if your morning blood sugar ranges are potentially dangerous (at, near, or over 300mg/dL).[3]

Measures to lower overall blood glucose levels can have a positive impact on the dawn phenomenon as they may lead to better glycaemic control. It’s important to remember that the dawn phenomenon is the result of natural hormonal changes, so it’s not something to be too worried about unless your blood sugar is extremely high in the mornings.

That said, there are some things you may want to try in order to prevent or ease blood sugar spikes in the early morning. The suggested approaches include:[4]

  • Varying the dosages of medications you take at night
  • Increasing evening exercise to lower blood sugar levels
  • Eating an earlier dinner
  • Increasing protein-rich nighttime snacks
  • Eating an early morning breakfast lower in carbohydrates

References

[1] O’Neal, T. B., & Luther, E. E. (2021). Dawn Phenomenon. In StatPearls. StatPearls Publishing. Accessible here.

[2] Chanoine, J. P., Rebuffat, E., Kahn, A., Bergmann, P., & van Vliet, G. (1995). Glucose growth hormone cortisol and insulin responses to glucagon injection in normal infants aged 0.5-12 months. Journal of Clinical Endocrinology and Metabolism, 80(10), 3032–3035. Accessible here.

[3] Checking your blood sugar levels | Diabetes testing | Diabetes UK. (n.d.). Retrieved April 26, 2021, from Diabetes UK.

[4] The dawn phenomenon: What can you do? - Mayo Clinic. (n.d.). Retrieved April 26, 2021, from Mayo Clinic.

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