Journal of Diabetes Research and Management

Blood Sugar Level

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Glycemia or blood glucose level also known as blood sugar level, refers to the amount of glucose present in the blood. The body cautiously controls blood sugar content to maintain metabolic balance.

For a 70 kg person, blood plasma contains approximately four grams of dissolved glucose at all times. When glucose is not circulating in the blood, it is stored as glycogen in the liver and skeletal muscles. In individuals who are fasting, the body keeps blood glucose levels stable by releasing just the right amount of glucose from these glycogen reserves in the liver and muscles to maintain homeostasis. Through the bloodstream, glucose can be transported from the intestine to other body tissues. The uptake of glucose by cells is mainly controlled by insulin, a hormone made in the pancreas. Once glucose enters the cell, it can be used as an energy source through the process of glycolysis.

In humans, maintaining proper glucose levels is essential for the normal functioning of various tissues, including the brain, which uses about 60% of blood glucose in individuals who are fasting and sedentary. When blood glucose levels remain elevated over time, it can lead to glucose toxicity, resulting in cell dysfunction and a range of complications associated with diabetes. Glucose levels are typically at their lowest in the morning, before the first meal, and they tend to rise for an hour or two after eating, increasing by a few millimoles per litre.

When blood sugar levels remain abnormally high, it is known as hyperglycemia, while low levels are termed hypoglycemia. Diabetes mellitus is marked by ongoing hyperglycemia due to various factors and is the most significant condition associated with impaired blood sugar regulation. Additionally, diabetes can lead to frequent instances of low blood sugar, or hypoglycemia. There are several methods available for testing and measuring blood sugar levels.

Normal blood glucose levels for non-diabetics, when tested while fasting, should range from 3.9 to 5.5 mmol/L. The American Diabetes Association states that for diabetics, the target fasting blood glucose range should be between 3.9 and 7.2 mmol/L, and it should be less than 10 mmol/L two hours after meals, as measured by a blood glucose monitor.

It is vital to note that normal value ranges can vary slightly from one laboratory to another. When glucose homeostasis is functioning properly, it helps maintain blood sugar levels within a narrow range of about 4.4 to 6.1 mmol/L, as determined by a fasting blood glucose test.

On a global scale, the average fasting plasma blood glucose level in humans is approximately 5.5 mmol/L; however, this level can fluctuate throughout the day. For individuals without diabetes who are not fasting, blood sugar levels typically remain below 6.9 mmol/L.

With varying intervals between meals or occasional high-carbohydrate meals, human blood glucose levels generally stay within the normal range. However, shortly after eating, non-diabetics may experience a temporary rise in blood glucose levels, reaching up to 7.8 mmol/L or slightly higher.

The real concentration of blood glucose and body fluids is quite small. For instance, in a healthy adult male weighing 75 kg with a blood volume of 5 L, a blood glucose level of 5.5 mmol/L corresponds to about 5 grams, which is roughly equivalent to a teaspoon of sugar. This small amount is partly due to the fact that enzymes alter glucose by adding phosphate or other groups to facilitate its entry into cells.