What can Cause a High Fasting Blood Sugar?

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  • Written By: M.R. Anglin
  • Edited By: Kristen Osborne
  • Last Modified Date: 26 September 2019
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There are many factors that can cause high fasting blood sugar, which is when a person has too much sugar in his blood stream after eight hours of not eating. Some common causes include too much insulin or blood pressure medication taken at night, a bodily process known as the "dawn phenomenon," and a person’s basal secretion processes being damaged. Fasting blood sugar is generally measured after a person wakes up in the morning, before he eats breakfast.

Taking too much blood pressure medication or insulin at night may cause a spike in fasting blood sugar. While the purpose of taking insulin is to reduce a person's blood glucose level, if he takes too much before he sleeps, the body may actually raise the blood sugar during the night. The same phenomenon can happen if a person takes too much blood pressure medication — the body may raise blood pressure during the night. People who experiences these phenomenon may wake up in the middle of the night with their hearts pounding and feeling dizzy or nauseous. If a person experiences this, he should speak to a doctor about adjusting his medications or the dosages thereof.


An occurrence known as the "dawn phenomenon" can also cause high fasting blood sugar. Before person wakes up, the body prepares for action by releasing blood sugar that has been stored in the liver. Because of this, the person will be able to get up and be active in the morning. In some people, this can cause the fasting blood sugar to surge too high. To counteract this, a person can have a snack before bed in order to prevent the liver from releasing sugar during the predawn hours.

A person who has does not have a proper basal secretion process may also have high fasting blood sugar. Usually, a person’s body will secrete a small amount of insulin periodically so the body can use blood sugar between meals. If that process becomes damaged, the liver may recognize the lack of insulin as a sign to start secreting more sugar into the blood stream. In order to reverse this, a person may have to take insulin. Before taking any action to correct this issue, a patient should see a doctor so she can diagnose the problem and prescribe insulin or other medications.

A person can often control high fasting blood sugar by eating a snack before going to sleep, changing the timing of the medications they take at night, or exercising before bed. It is important, however, to speak to a doctor for the best tips and guidance in controlling blood sugar, especially if it means changing the timing or dosage of a prescribed medication. Interestingly, a person with high fasting blood sugar may have normal blood glucose during the rest of the day. Conversely, a person with a normal fasting blood sugar may wrestle with high blood glucose throughout the day. Therefore, a person who is concerned about their blood glucose level should check it at various times to get the most accurate reading.


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Post 1

It's always best to check in the morning and two hours after each meal to get the best handle on how your blood sugar levels are running.

Having said that, the dawn phenomenon is one of the more puzzling aspects of diabetes, but also one of the easier ones to fix -- usually. A snack before bed helps, but it needs to be a specific kind of snack: a protein based one. Peanut butter on crackers, a piece of cheese, a piece of lean meat or a handful of nuts are all great choices. What this does is it gives the liver something to do besides dump glucose, since it is working to help metabolize the protein.

A diabetic with high fasting readings can always try the late snack first, since it won't run the glucose up, and check the results for several days, to see if he or she is experiencing DP.

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