Blood sugar level regulation is complex with contributions from many different systems. These multiple controls are designed to keep a steady supply of glucose to the brain. Brain metabolism depends primarily on glucose for fuel. If the amount of glucose supplied by the blood falls, the brain is one of the first organs affected.
There are a number of mechanisms that tightly regulate (outside of a disease state) the level of glucose (sugar) in the blood stream. When there is a plentiful supply of glucose, such as after a carbohydrate-containing meal, glucose is absorbed from the intestine, and the level of blood glucose (sugar) rises.
Glucose is removed from the blood stream by uptake into virtually all cell types, but most importantly into muscle and adipose (fat) tissue. This removal requires insulin. Insulin, which is released from the pancreas, acts to decrease the level of glucose in the blood by signalling these cells to pick up and store glucose.
Insulin also inhibits breakdown of glycogen (glycogenolysis) and formation of glucose from non-carbohydrate sources (gluconeogenesis). The central nervous system can also sense glucose levels and act to affect the blood sugar levels, at least in part by regulating gluconeogenesis.
The importance of an adequate supply of glucose to the brain is apparent from the number of nervous, hormonal and metabolic responses to a falling glucose level (1). Most of these are defensive or adaptive, tending to raise the blood sugar via
Glycogenolysis - breaking down of glycogen, a polymer of glucose molecules, stored in the liver and muscle. If the blood sugar level falls too low the liver converts a storage of glycogen into glucose and releases it into the bloodstream, to prevent the person going into a diabetic coma, for a short period of time.
Gluconeogenesis - a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids.
Below is a diagram from the journal Nature, demonstrating the body’s regulating mechanisms for maintaining the appropriate glucose levels in the blood.
Adipocytes as regulators of energy balance and glucose homeostasis (2)
Evan D. Rosen and Bruce M. Spiegelman Nature 444, 847-853(14 December 2006)
Sometimes blood sugar levels fall too low. This is called hypoglycemia. Hypoglycemia can happen when a person eats too little food, takes too much insulin or diabetes medicine, or is more physically active than usual. Hypoglycemia is less common in non-diabetic persons, but can occur at any age. Among the causes are excessive insulin produced in the body (hyperinsulinemia), inborn errors of metabolism, medications and poisons, alcohol, hormone deficiencies, prolonged starvation, alterations of metabolism associated with infection, and organ failure.
Often hypoglycemia happens suddenly, and sometimes there is no explanation for why it occurs. When this happens, a person may have some, or all of these symptoms (3):
Weakness or feeling very tired
Since hypoglycemia can be life-threatening, it must be treated immediately.
Recommendations from the NY Department of Health for treatment of hypoglycemia: If you have any of the symptoms of hypoglycemia, check your blood glucose. If the level is 70 or below, have one of the following quick acting sources of sugar right away:
3 or 4 glucose tablets
1 serving of glucose gel (equal to 15 grams of carbohydrate)
1/2 cup (4 ounces) of any fruit juice
1 cup (8 ounces) of milk
1/2 cup (4 ounces) of a regular (not diet) soft drink
5 or 6 pieces of hard candy
1 tablespoon of sugar or honey
After 15 minutes, check your blood glucose again to make sure your level is 70 or above. Repeat these steps as needed. Once your blood glucose is stable, if it will be at least an hour before your next meal, have a snack.
If you take diabetes medicines that can cause hypoglycemia, always carry a quick acting source of sugar for emergencies. It’s a good idea also to wear a medical identification bracelet or necklace.
You can usually prevent hypoglycemia by eating regular meals, taking your diabetes medicine, and checking your blood glucose often. Checking will tell you whether your glucose level is going down. You can then take steps, like drinking fruit juice, to raise your blood glucose.
Most hypoglycemic reactions are mild and can be resolved within 10 to 15 minutes of receiving the treatments listed above. Sometimes, hypoglycemia can happen rapidly and may progress to a more serious stage where a person becomes unconcious, has a seizure, or is unable to swallow. If this happens, nothing should be given by mouth. This is an emergency situation and 911 should be called immediately.
There is a life-saving treatment called glucagon that can be given by injection in an emergency. Glucagon is a hormone made in the pancreas and raises glucose levels. Glucagon helps to reverse the symptoms of hypoglycemia. A glucagon emergency kit can be ordered by a doctor or health care provider and carried with the person who has diabetes in case of emergencies. Even if glucagon is given, 911 should be called. Glucagon will not harm a person, but sometimes may cause vomiting or nausea.
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