How to control high fasting blood sugar in the morning
- Lucy Zhang, RD, CDE
- 3 hours ago
- 4 min read
“My blood sugar is high before I even eat anything!”
If this sounds familiar, you’re not alone. Waking up to an elevated fasting blood sugar is one of the most common frustrations I hear from clients. Even when you’re putting in the work (balancing your meals, moving your body, and keeping post-meal numbers in check), that morning reading can feel discouraging. The truth is, fasting blood sugar is influenced by more than just what you ate the night before, and understanding why it runs high is the first step toward getting it back into range.
What is fasting blood sugar?
Fasting blood sugar refers to blood sugar levels at least 8 hours after eating or drinking anything other than water. Most commonly, this refers to blood sugar in the morning before you eat breakfast.
What is considered a high fasting blood sugar level?
Fasting blood sugar (fasting glucose) is one of the lab tests that can be used to diagnose prediabetes or diabetes.
In Canada, fasting blood sugar of ≥7.0 mmol/L is considered to be in the diabetes range. Fasting blood sugar of 6.1 - 6.9 mmol/L is considered to be in the prediabetes range. Where as 6.0 mmol/L or less is considered normal range.
What should fasting blood sugar be for someone with diabetes?
For most people living with diabetes, the target for fasting blood sugar is 4 - 7 mmol/L. Your physician or healthcare team may recommend an individualized target range that’s different.
What causes high fasting blood sugar?
High fasting blood sugar can be caused by various physiological and lifestyle factors. These include:
The dawn phenomenon. This refers to the rise in blood glucose we see close to when someone is waking up. Overnight, our liver naturally releases stored sugars to prevent blood sugar from dipping too low. Hormonal changes that occur (e.g. increase in growth hormone release) prior to someone waking up signals the liver to release more stored sugars. The hormonal changes may also cause increased insulin resistance in the morning (resulting in higher postmeal blood sugar after breakfast as well).
Somogyi effect. This refers to high blood sugar resulting from a rebound effect after having a hypoglycemic (low blood sugar) event overnight. This can sometimes happen in individuals who take medications with a risk of low blood sugar.
Overnight data from a continuous glucose monitor (e.g. Freestyle Libre 2, Dexcom G7) can show this.
Alternatively, if you rely on fingerpricking. If you are waking up in the middle of the night, it would be recommended to check blood sugar to see if you are having any lows.
High carbohydrate meals or snacks in the evening. Of course, an extra indulgent meal can cause blood sugar to stay higher postmeal, resulting in higher overnight and fasting blood sugar.
Dinner late at night. Similarly, eating dinner late into the evening can mean that glucose is still being digested or absorbed close to or during sleep. As we can be less insulin-sensitive at night (when the body is winding down for the day), this can result in blood sugar staying high for longer, causing higher fasting blood sugar.
Inadequate or poor quality sleep. Inadequate sleep results in higher levels of stress hormones (e.g. cortisol), which can result in the liver releasing more stored glucose than you need. Poor sleep can also result in temporarily increased insulin resistance, making your body is less efficient at using your own insulin.
What can you do to improve fasting blood sugar?
Eat an earlier dinner
If you eat a late dinner, consider shifting the timing of your dinner a couple of hours earlier, to allow more time for blood sugar to recover postmeal before sleeping.
Try incorporating a small evening snack
Test out if an evening snack of 15g or less of complex carbohydrate paired with protein improves fasting blood sugar at all. This may sound counterintuitive, but for some people, having a small balanced snack can act as a stop sign to the liver, as if to say “hey, I’m giving my body a little extra fuel, I don’t need so much stored sugars to be released”. It’s worth experimenting with a few different snack options here to see what works best for you.
Include some gentle exercise into your evenings
Exercise can help to temporarily increase your body’s insulin sensitivity, helping to bring blood sugar down sooner overnight. Thus, resulting in lower fasting blood sugar.
Aim for at least 7 hours of sleep each night
It’s worth noting that the quality of your sleep is also important. So to optimize blood sugar, protect your sleep!
Implement stress management strategies
Whether that’s mindful breathing techniques, tucking into a good book, going for a walk for some fresh air, or watching your favourite feel good movie, take time to focus on stress reduction. This can help to lower stress hormones, improving your body's insulin sensitivity.
