Dr Paul Mason

What is a high glucose level?

5 mins read

Diabetes can be a devastating disease, doubling our risk of heart disease and being the single most common cause of kidney failure and amputations, amongst other things. These potential consequences of diabetes are largely due to the presence of high levels of glucose in our blood.

What is glucose?

Glucose is the sugar that makes up carbohydrates, which is why carbs can cause problems for people with diabetes. Nonetheless, we do need some glucose in our circulation; the problem is when we have too much glucose. In fact, a healthy person should only have about 4 grams or a teaspoon of glucose in their circulation at any point – about a quarter of the amount of carbs that can be found in a single slice of bread.

What does glucose do to the body, and why do glucose levels matter?

Excess blood glucose actually binds to and damages proteins it comes in contact with. This is called glycation, resulting in advanced glycation end products (AGEs) – essentially proteins damaged by sugar. While this process does occur normally, it is vastly accelerated in diabetes. Amongst other things, levels of AGEs correlate with heart disease, stroke, cancer, dementia, arthritis and even aging of the skin. There is no doubt AGEs make healthy aging difficult, if not impossible.

In patients with type 2 diabetes where the normal method of removing glucose from the blood is impaired, the glucose derived from carbohydrate foods such as bread, pasta and potatoes can lead to massive rises in blood glucose levels. The question is, how much glucose is too much?

What are normal glucose levels?

We measure glucose levels by counting the number of glucose molecules per litre in the blood (mmol/L). Most of the time blood glucose levels are measured in the early morning, before any food. This is known as a fasting level. A fasting glucose level of 7.0mmol/L or more is consistent with diabetes. Even fasting glucose levels of less than 7.0mmol/L can be problematic, however. A level of 5.6mmol or more is considered pre-diabetes, while research indicates the lowest chance of dying occurs with fasting glucose levels between 4.4 to 5.2 mmol/L.

Glucose levels can also be measured with an oral glucose tolerance test, where blood glucose levels are measured over two hours following a drink containing 75 grams of glucose. A two-hour glucose level of over 11.1 mmol/L, consistent with diabetes, is associated with more than double the chance of dying compared with someone with a two-hour glucose level of less than 6.1 mmol/L.

Average blood glucose levels can also be estimated with a measurement known as haemoglobin A1c, or HbA1c for short. Your red blood cells circulate in your blood’s fluid, which also contains glucose molecules. These glucose molecules, over time, will attach to your red blood cells: the more glucose that is present, the more which will attach to your blood cells.

Therefore, measuring the number of glucose molecules on each red blood cell shows your average glucose level. Of course, many factors can interfere with this measurement, including other factors in your blood that inhibit the binding of glucose to red blood cells (glycation inhibitors), as well as variations in the lifespan of your red blood cells.

Ironically, conditions in which red blood cells are being excessively destroyed will lead to an overall population of younger red blood cells with an artificially low reading. The reverse is true for people with longer-lived red blood cells, with their HbA1c overestimating their average glucose level. These limitations aside, HbA1c can be used to both diagnose and monitor diabetes. An HbA1c of 6.5% of more may indicate you have diabetes, while reductions over time indicate improved glucose control.

It’s interesting that traditionally doctors do not recommend diabetic patients to aim for a ‘normal’ HbA1c between 4.0 – 5.6% while under standard medical care. This is because combining a high carbohydrate diet, as the dietary guidelines recommend, with diabetes medications usually results in significant fluctuations in blood glucose levels. To obtain normal HbA1c could mean periods when the blood glucose level is low, a state known as hypoglycemia which is potentially dangerous. Of course, this is quite different to controlling your blood glucose level with diet, and many people with diabetes can achieve a normal HbA1c by following a low carbohydrate diet.

Risk factors of high glucose levels

It is not just long-term consequences that arise from high blood glucose levels. Problems can arise rapidly should the glucose levels be high enough. One of the most obvious problems with high glucose levels arises when our kidneys can no longer prevent glucose from entering our urine. This is known as glycosuria and can lead to several issues, including dehydration due to excessive urination and increased risk of bladder infection.

Symptoms of high glucose levels

One potential indication of both glucose in the urine and kidney damage is increased urination, especially overnight. The dehydration that results often leads to prominent thirst. Be sure to consult with your doctor if you notice these symptoms. It is generally considered that this leaking of glucose into the urine occurs whenever blood glucose levels exceed approximately 10 mmol/L. Note that this level is almost certainly being exceeded regularly in people with diabetes following the dietary guidelines. Perhaps even more of a problem is that this threshold is likely lower when the kidneys are damaged, as is common in diabetes.

You may have also heard of fructose. Fructose is the other half that, together with glucose, makes up sucrose, or table sugar. And fructose can be even more of a problem than glucose. For example, fructose damages proteins about seven times more than the same amount of glucose and is a much more potent cause of fatty liver disease. The thing is, fructose is not glucose. And that means it is overlooked when measuring your blood glucose. This is why 100 grams of table sugar (sucrose) won’t have the same impact on your blood glucose levels as 100 grams of pure glucose, but it is clearly worse for your health.

Dr David Unwin from the UK famously developed an infographic adopted by the UK National Health Service (NHS) demonstrating the sugar content of various foods in teaspoon amounts. For simplicity, he presented all sugar as glucose when technically, he should also have included fructose. His critics used this to denigrate this valuable educational tool solely because some foods didn’t contain the specific amount of glucose indicated. While technically correct, the fructose contained in some foods is even more damaging to health than glucose. So yes, certain foods didn’t contain as much glucose as suggested, but the truth was even worse. The ‘missing’ glucose was actually fructose, a much more damaging sugar.

Treatment of high glucose levels

The solution to addressing excessive blood glucose levels essentially comes in two parts. First of all, is the problem of reducing the source of glucose in the first place. If one understands that carbohydrates are literally made from glucose, then it is only common sense that they should be avoided.

The other half of the problem is the metabolic damage present in people with diabetes that limits their capacity to process dietary carbohydrates. In addition to carbohydrates, dietary fructose (found in sugar) and vegetable oils are major contributors to this metabolic damage. The Defeat Diabetes Program focuses on these principles in assisting you to manage and potentially even put your diabetes into remission.

Related articles

Your health and your wallet: The true cost of type 2 diabetes
From quick-fix to lasting success: A new approach to Ozempic
By Defeat Diabetes

< 1 min read

7 low carb lunch ideas for busy days
By Defeat Diabetes

< 1 min read

Type 2 diabetes and low carb: Is it for you?
By Defeat Diabetes

< 1 min read

5 easy low carb hearty dinners
By Defeat Diabetes

2 mins read

The essential guide to low carb vs low GI

Join Australia's first doctor-led, evidence-based program transforming the lives of those with pre-diabetes, type 2 diabetes and other chronic conditions.

  • Deep-dive lessons
  • Video masterclasses
  • Easy-to-read articles
  • 250+ low carb recipes
  • Weekly meal plans
  • Community support