The blood glucose levels are maintained within a narrow range by two important regulating hormones – insulin and glucagon. Other factors also influence blood glucose levels but the action of these two hormones have the most profound effect.
Simply, the body can raise the blood glucose levels when it falls below a normal level mainly due to the action of glucagon and lowers the blood glucose levels when it rises into a high range by the action of insulin. Both these hormones are primarily secreted by the pancreas – alpha cells (glucagon) and beta cells (insulin) of the islet of Langerhan’s.
Other hormones like epinephrine, growth hormone and cortisol also influence the blood glucose levels but usually act in severe or prolonged hypoglycemia (low blood glucose levels). These hormones cannot regulate the blood glucose levels to the same extent as the pancreatic hormones, glucagon and insulin. Digestive hormones like somastatin can also affect blood glucose levels by delaying gastric emptying and reducing absorption of glucose in the small intestine.
The liver plays an important role in glucose regulation. Insulin causes almost two-thirds of the excess glucose in the blood stream to be stored in the liver. Glucagon stimulates the process of gluconeogenesis where the liver releases stored glucose (glycogen) and produces glucose from fats and proteins.
Importance of Normal Blood Glucose Levels
Glucose is used by all cells in the body to produce energy and maintain life-sustaining processes. While the body’s cells can use fats and protein for energy production if necessary, the brain cells however require glucose to continue functioning. Other cells, like those in the eye and and gonads, are also dependent on sufficient levels of glucose in order to continue functioning as normal.
On the other hand, high levels of glucose in the blood (hyperglycemia) and tissue spaces can hamper normal cell functioning and disrupt homeostasis. Various cells are damaged by high levels of glucose and this is seen in diabetes mellitus (sugar diabetes) where long periods of elevated glucose levels damage the nerve cells and lining of the blood vessels. This affects nerve functioning and can lead to a host of vascular diseases that can ultimately lead to death.
Elevated blood glucose levels also affects the water and electrolyte balance of the body. Water is drawn out of the cells (osmosis) and high levels of glucose in the urine causes the excretion of electrolytes (osmotic diuresis). This leads to dehydration that can affect the functioning of various organs, particularly the cardiovascular system, and over time lead to death.
Range of Blood Glucose Levels
Normal Blood Glucose Levels
The body’s glucose regulating system maintains the fasting blood glucose levels within a range of 70 to 99 mg/dL (3.9 to 5.5 mmol/L). Approximately 1 hours after eating a meal, the blood glucose levels will rise to a maximum of 120 to 140 mg/dL (6.6 to 7.8 mmol/L) and this gradually settles by 2 hours. Normal blood glucose levels will not exceed 140 mg/dL after eating, even if you have eaten a large meal or sugar-laden foods.
Low Blood Glucose Levels
Blood glucose levels below 54mg/dL (3 mmol/L) are indicative of hypoglycemia if it meets with the guidelines outlined in Whipple’s triad. Read more on What is Low Blood Sugar?
Diabetes Blood Glucose Levels
In pre-diabetes (impaired glucose tolerance) and diabetes mellitus (sugar diabetes) the fasting and post-prandial (after eating) blood glucose levels differ. These higher than normal levels does not mean that it is normal but since glucose tolerance/regulation is impaired, the levels are not sustained within the normal range.
The fasting blood glucose levels in pre-diabetes varies but does not exceed 125mg/dL (6.9 mmol/L). After eating, the blood glucose levels rise but remain below 200 mg/dL (11.1 mmol/L). Levels aboves this value is indicative of diabetes mellitus.
In diabetes mellitus the fasting blood glucose levels may vary between 70 to 140 mg/dL (3.9 to 7.8 mmol/L). Values rise significantly after eating and may exceed 200 mg/dL (11.1 mmol/L). Higher levels may be seen in poorly managed or uncontrolled diabetes mellitus.