The Dawn Phenomenon: What It Is and How to Fix It

The Reason Your Blood Sugar Could Be Elevated in the Morning

In This Article

Woman waking up in bed
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If you've recently tested your blood glucose before breakfast and were surprised that it was higher than usual, it could be an effect of something called the dawn phenomenon, a hormonal surge that causes elevated morning glucose. If you have diabetes, it could raise your fasting glucose levels much higher than normal. Find out what causes this hormonal hyperglycemia and how you can prevent it.

Who Is Affected

Everyone experiences the dawn phenomenon, regardless of whether you have diabetes. The only difference is in how we react to this effect. According to the American Diabetes Association, people with diabetes simply don't have the normal insulin response to automatically adjust for this phenomenon, and that's why their blood sugar may creep up to even higher levels.

Causes

During the evening hours, your body produces less insulin. But while you're sleeping, around 4 to 8 a.m., certain hormones tied to the circadian rhythm start to take action to get glucose circulating in the body to be used for cellular energy for the day ahead. Hormones such as cortisol, adrenaline, glucagon, and growth hormone each trigger the body to pump out more glucose from the liver and muscles, but this combined with the lack of insulin in circulation results in a natural blood sugar rise in the morning.

While the dawn phenomenon is totally normal for most people, it can be amplified in those with diabetes who have greater insulin resistance. If you suddenly realize your fasting morning glucose is soaring, it could be related to not taking an adequate dose of insulin at night, missing your evening diabetes medication, or overeating carbohydrates at dinner or bedtime.

Treatment

The counter-regulatory hormones causing glucose to increase can make morning glucose tougher to treat in people with diabetes. You may need more medication (if you aren't missing doses). Sometimes, changing the timing of your medication can also help to reduce morning blood sugar. 

These additional tips can help to counteract the dawn phenomenon:

  • Reduce your carb intake: Cutting back on carbs (at least during dinner and evening hours) could help you counteract a morning glucose burst.
  • Exercise in the evening: Going for an after-dinner walk, bike ride, or jog may help keep morning blood sugars in a better range.
  • Skip the late-night snack: If you're truly hungry, choose something fat- and protein-based that won't raise your glucose much, like nuts or cheese.
  • Get a good night's sleep: Aim for six to eight hours each night, as fewer than six hours of sleep has been shown to significantly raise blood sugar levels.
  • Eat breakfast: Even if your blood sugar is high, as eating something will actually shut down the dawn phenomenon process and help your blood sugar return to normal.
  • Test regularly: The only way to know what's normal for your body is to frequently test your blood sugar. As the level will fluctuate throughout the day, a slight elevation may not be too far out of the ordinary for you.

Check your eligibility for a continuous glucose monitor (CGM)—a small device that measures real-time glucose 24 hours a day. Alarms can sound off when your blood sugar is trending high or low, even at night.

The Somogyi Effect

Occasionally, though less often, the problem of elevated morning fasting glucose may be due to something called the Somogyi effect, which is caused by rebound hyperglycemia (high blood sugar) after an episode of hypoglycemia (low blood sugar) while you are sleeping. Most common in people with type 1 diabetes, this can happen if you take nightly insulin. The Somogyi effect seems to occur more often in those on higher doses of insulin. 

It can also happen if you take insulin and your bedtime blood sugar was on the lower side and you didn't eat a snack before bed. In either case, your blood sugar drops during the night and your body releases hormones to counteract the drop. The result? You wake up with a higher than normal blood glucose level.

If you have type 1 diabetes and are experiencing this effect, be sure to let your doctor know. They may need to change your medication or insulin dosages. If you are taking insulin, monitor your blood sugars before you go to bed. If you are too low, for example, less than 100 mg/dL (each reference range is different for each individual), you may need to have a snack before bed that consisting of some protein, fat, and a small amount of carbohydrates. For example, a handful of berries and plain Greek yogurt or half a nut-butter sandwich on whole-grain bread. 

How to Tell the Difference

The best way to know for sure whether you're experiencing the dawn phenomenon or the Somogyi effect is to test your blood sugar in the middle of the night. Wake up sometime between 2 and 3 a.m. for several nights in a row and check your blood sugar. If you are low at that time (<70 mg/dL), it could be the Somogyi effect. If you are normal or high, then the dawn phenomenon may be the culprit. You'd need to do this a few nights in a row to determine whether or not this has become a pattern warranting a change or if it was just a fluke episode.

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Article Sources

  • American Diabetes Association. Dawn Phenomenon. 

  • Choudhary P, Davies C, Emery CJ, Heller SR. "Do high fasting glucose levels suggest nocturnal hypoglycaemia? The Somogyi effect-more fiction than fact?" Diabet Med. 2013 Aug;30(8):914-7. doi: 10.1111/dme.12175.