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A person scanning their CGM with a smartphone
A person scanning their CGM with a smartphone

Glucose is an essential energy source for human life. In fact, both simple and complex sugars are broken down into glucose by the digestive system for our cells to use. Once in the blood, glucose is taken into cells by insulin, a hormone produced by the pancreas and used throughout the body.

Depending on the source of glucose, levels of glucose in the blood can “spike,” or rapidly increase then decline as the glucose is taken into cells or stored as glycogen or fat. Eating a sugary meal is probably the most direct way to cause a spike, but it can also happen with intense exercise, as your body stimulates the release of glycogen or creation of new glucose for immediate use.

In both cases, the short elevation in blood glucose is a sign your body is functioning normally and handling glucose in a way that sweeps it out of your blood when you don’t need it and back in when you do. If blood glucose is regularly too high, however, it may be a sign that something has gone awry with how your body handles glucose.

One of the most common reasons for long-term high blood glucose levels is diabetes mellitus, in which the body has lost the ability to produce or respond to insulin and glucose remains elevated in the blood. There are also, however, several other reasons short of diabetes mellitus for persistently elevated blood glucose.

Some are related to chronic psychological stress, others to dietary habits and patterns, and others still simply depend on how someone responds to their own unique mix of foods and drinks, exercise patterns and environmental factors. Here then is a short list of reasons, aside from diabetes mellitus, for chronically elevated blood glucose levels:

14 Reasons Your Blood Glucose Levels Won’t Go Down 

1) Dehydration

In the simplest possible case, a severe lack of water intake can lead to increased concentration of most everything in blood since the total amount of water in the body (blood volume is the denominator in any blood concentration) eventually declines. The authors of a review on the subject also found that copeptin, whose levels in blood increase even in less severe dehydration, is also an independent risk factor for the later development of DMT2.

2) Eating Late at Night

Our bodies process food and carbohydrates best during daylight hours, so eating large meals later in the evening, especially those with high sugar content, can lead to higher and longer blood glucose responses. In some cases, the glucose elevations can persist into the morning, depending on the metabolism of the individual.

3) Large Meals High in Both Carbohydrates and Fat

Eating a large meal that is high in both carbohydrates, which are metabolized relatively quickly, and fats, which take more time to digest, can cause a prolonged elevation in blood glucose.

Often we see glucose responses to these meals taking 5 or more hours to return to normal, where 2-3 hours is the recommended amount of time. Meals high in carbohydrates and fat would include fried foods, cheesy pastas, pizza, etc. The fat in the meal slows down the digestion and absorption of the glucose, causing the glucose to slowly be processed over a long period of time.

a person standing on the scale and tape measure

4) Obesity

As an independent risk factor for developing DMT2, obesity is a cause of both insulin resistance and high blood glucose, which causes the pancreas to try and work harder to shuttle glucose from the blood into cells. One reason for this could be that fat cells, or adipocytes, release fatty acids into blood that reduces the intake of glucose by cells.

Another potential reason is that overfilled adipocytes cause mild chronic inflammation that, although not severe enough to cause obvious symptoms, can have an influence on the handling of glucose in the blood. 

5) Sedentary Lifestyle

Exercise at any level and duration has a positive impact on insulin sensitivity – diabetes mellitus type 2 (DMT2) is defined by resistance to insulin. Use of muscles either for cardio or weight training leads to increased glucose uptake by those muscles, which use it as fuel.

The subsequent risk of developing DMT2 is reduced by over half when exercise is combined with moderate weight loss. Even in populations with advanced DMT2 exercise is helpful, so especially for the rest of us this is a nearly riskless way to improve metabolic health.

a person looking sad

6) Stress

While insulin and glucagon control blood glucose levels directly, the stress hormone cortisol also leads to increased blood glucose. This is an essential part of the “fight or flight” response, because a short-term stressor like discovering a predator or realizing a possession is missing could lead to increased demands for glucose as the body needs to run or engage in combat.

Today, more often these stressors are related to work or home life, and unfortunately many tend to be chronic instead of acute in nature. This chronic stress response can cause our glucose levels to be persistently elevated.


7) Steroids

In some cases, people are prescribed steroids like dexamethasone or cortisone that have similar effects as the naturally produced steroid hormone cortisol. For this reason, such prescriptions are often short-term to avoid the consequences of chronic “stress,” but in rarer cases longer prescriptions are needed.

a person holding a burger on one hand and an apple on another

8) Eating Habits

For better or worse, one popular eating habit is known as “grazing,” in which someone eats small amounts of food throughout the day. Although this has a certain appeal, the predictable result is that blood glucose is constantly elevated even if the food is relatively low in carbohydrates since intake is so frequent.

9) Endocrinopathies

In very rare cases, long-term high blood glucose levels can be caused by an endocrine disorder (other than diabetes mellitus) that causes persistently high levels of cortisol or glucagon.

10) Non-Endocrine Illness

More common illnesses, such as when we have a cold or the flu, can result in consistently increased glucose values. When we have a cold or flu, our body deploys many different hormones which heighten our immune response to fight off the cold.

It is similar to our stress response, and an unfortunate downside is that this shift in hormones causes us to make more glucose and to be slightly less sensitive to the effects of insulin.

a person laying in bed and turning off an alarm

11) Sleeplessness

A large review of studies looking at sleep duration and quality, including the presence of obstructive sleep apnea (OSA), concluded that even in healthy individuals lack of sleep causes high blood glucose levels.

12) Alcohol

While drinking alcohol (ethanol), there is a short-term decrease in blood glucose levels followed by an increase in blood glucose lasting hours to days. This may be due to a change in insulin and glucagon balances or because the liver prioritizes the metabolization of ethanol, which is technically a toxin (hence “intoxicated”), over the normal process of storing glucose as glycogen.

13) Female Hormones

In a long-term study of hundreds of premenopausal women, insulin levels and insulin resistance both increased around ovulation and for several days afterwards, although blood glucose levels over this same period was slightly lower.

Since the blood measurements were taken after 12 hours of overnight fasting, the question of how this transient change in insulin resistance would affect blood glucose levels remains open considering the concurrent increase in insulin levels. Every woman is different, but with our data we have found that many people experience slightly higher glucose levels during the luteal phase of their menstrual cycle. 

14) Gut Microflora

The collection of non-human life in the intestine is known as the gut microflora, and it is an important component of intestinal health. Likewise, when it is out of equilibrium, there can be unfavorable consequences for the rest of the body. The main ways it can influence blood glucose include reduced insulin secretion, release of fatty acids and changes in adipocyte inflammation and activity.

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Kara Collier

Reviewed by: Kara Collier RDN, LDN, CNSC

Kara Collier is the co-founder and VP of Health at Nutrisense, one of America’s fastest-growing wellness-tech startups, where she leads the health team. She is a Forbes 30 under 30 recipient, frequent podcast guest & conference speaker.