The blood sugar level is a measure of the glucose level in the blood, which is expressed in millimoles/mL. Blood sugar levels are maintained by the hormones glucagon and insulin, which are produced by the islets of Langerhans. These are located in the pancreas. Diet, exercise, stress and certain diseases can influence blood sugar levels. This article will briefly explain how this works.
What blood sugar levels mean
Blood sugar is a synonym for glucose. The blood sugar level is therefore the glucose level in the blood. This is expressed as millimoles/L. Hormones maintain blood sugar levels, as they rise and fall due to various influences. These influences will be discussed later in the chapter. The hormones insulin and glucagon, which are secreted by the islets of Langerhans, play an important role in this process. These ensure that glucose can be stored in the liver and muscles in the form of glycogen, and that this glycogen can be released again through the conversion of glycogen to glucose. A normal blood sugar level for healthy people is around 4.6 mmol/L before a meal and around 6.6 mmol/L after a meal. Figure 1 shows the amount of sugar and insulin and the blood sugar level in a healthy person.
Glucose
First we look at what exactly glucose is. Glucose has the molecular formula C6H12O6. This means that it is a molecule with six carbon atoms, twelve hydrogen atoms and six oxygen atoms. It belongs to the simple sugars that arise from the digestion of other sugars. Glucose is the most important fuel for our body. Glycolysis takes place in the mitochondria, where glucose is burned. This releases the energy-rich substance ATP, the fuel for many processes in the cell. Just as a car cannot function without gasoline, our body cannot function without glucose and ATP.
Glucose can also be stored in small stores in the liver and muscles. It is then called glycogen, a polysaccharide (chain of glucose molecules). The conversion of glucose into glycogen is called glyconeogenesis. This glycogen is then converted back into fat. If you need a large amount of energy quickly, this supply can be released.
Insulin
The hormones that contribute to maintaining the balance of blood sugar levels are then examined. These ensure that blood sugar levels remain at a constant level. Insulin is the most important hormone for blood sugar levels. It is made in the form of one long chain of amino acids, pro-insulin. This chain curls up and the disulfide bridges connect amino acids at the two ends. The intermediate piece, the connecting protein, is cut out.
Insulin lowers blood sugar levels. This happens in two different ways. The insulin that enters the blood firstly causes the glucose receptors of the body cells to work, causing the cells to absorb glucose. Insulin is in fact the substance that opens the doors of the cell so that the glucose molecules can be absorbed. Fat cells in particular often absorb glucose and then convert it into fat (triglycerides). In addition, the synthesis of glycogen in muscle and liver cells is stimulated. This is because the glucose then ends up in the portal vein after it has been absorbed by the intestinal wall. Insulin release is stimulated. Glucose and insulin are transported to the liver via the portal vein. There, the surplus of glucose is converted into glycogen. Except for the moments when there is a surplus of glucose, there is also a small amount of insulin present in the blood. This is necessary for the glucose uptake of many cells. This is called the basal insulin requirement. Without insulin, cells, with the exception of brain cells and red blood cells, are unable to absorb glucose. Then combustion cannot start to provide energy and keep the cellular mechanisms running.
Glucagon
Another polypeptide hormone is glucagon, but its action is opposite to that of insulin. Glucagon causes an increase in blood sugar levels. This stimulates the breakdown of glycogen into glucose in the liver and muscles, this process is called glycogenolysis. However, the store of glycogen is limited, namely a maximum of 150 grams in the liver and a maximum of 150-200 grams in the muscles. Moreover, the muscle glycogen can only supply glucose within its own muscle fiber, which is of no use to the rest of the body. The body will try to maintain this reserve for as long as possible, in case acute situations arise.
Furthermore, glucose can become available through gluconeogenesis. New glucose is formed in the liver, from amino acids and a small amount of lactic acid and glycerol. This is also stimulated by glucagon and has a large reserve capacity. Alcohol inhibits gluconeogenesis. When people fast for a long time, gluconeogenesis is the only source of the necessary glucose. Amino acids are then the only source of glucose. However, these are the building blocks of proteins, which all have a function. A reserve supply of proteins is therefore not present in the body, so gluconeogenesis will ultimately lead to reduced protein mass and a loss of organ functions. In that situation, the body switches to fat breakdown, lipolysis, for its energy supply. This releases glycerol and free fatty acids. The glycerol is then converted back into glucose in the liver.
Adrenaline
Adrenaline also affects blood sugar levels. It is produced in the medulla of the adrenal glands, which are located on the kidneys. This hormone is released during exercise, stress, anxiety, pain and large temperature differences. The processes for dissimilation are stimulated, causing the glucose level in the blood to rise, because glycogen is converted into glucose, releasing ATP (energy). Blood pressure also rises, causing more blood to flow to the muscles. This allows the muscles to exert many times greater forces, so that people can fight or flee. In addition to its function as a hormone, adrenaline is also a neurotransmitter, it can transmit impulses between nerve cells.
Pancreas
The formation of these hormones is regulated by the pancreas. This is a cluster-shaped, elongated gland and plays a major role in human digestion. The average size is about twelve to six inches long and one to three inches thick. This gland is located at the back of the upper abdomen, the head is located in the bend of the duodenum, while the tail slopes upwards to the left, behind the stomach. The pancreas therefore plays an important role in regulating blood sugar levels. This is one of the two functions of the pancreas, namely the endocrine function. The exocrine function contributes to digestion. The hormones insulin and glucagon are produced in the pancreas, in the Islets of Langerhans, which are found throughout the pancreas. Glucagon is produced in the α cells, insulin is produced in the β cells. The pancreas can respond to the amount of glucose in the blood. When blood sugar levels are too high or when food is thought or smelled, the pancreas produces the blood sugar-lowering hormone insulin. Glucagon is produced when blood sugar levels are too high.
Influences on blood sugar levels
In healthy people, small fluctuations in blood glucose levels during the day are normal. However, sharp drops, hypoglycemia, and rapid peaks, hyperglycemia, can occur. There are many different factors that can cause fluctuations in blood sugar levels. The factor that most influences blood sugar levels is diet. This affects not only what is eaten, but also the way in which food is eaten and with what regularity. Certain foods have a greater impact on blood sugar levels than other foods.
Glycemic index
The glycemic index (GI) gives an idea of this. This index is a measure of the effect that food has on blood glucose levels, or the speed at which glucose levels rise after eating certain foods. A food with a low GI, i.e. below 55, is considered a good food with good sugars. This prevents glucose from being converted into glycogen, which in turn is converted into fat. In addition, a slow release of energy is better than a rapid peak, which occurs after eating foods with a high GI, i.e. 70 or higher. These are foods that can be digested quickly.
Creatine
The substance creatine, which is said to provide extra muscle strength, explosiveness and endurance, has been scrutinized by scientists. Research has been done into the response of blood sugar levels when using creatine. This has shown that the blood sugar level responds more strongly to glucose ingestion, after six weeks of using creatine, than in a control group. This effect is a 30% higher blood sugar level (when ingesting glucose). There were no significant differences in the fasting glucose levels.
Medicines that are not part of the food, but are taken, may also have an influence on blood sugar levels. It is therefore important to discuss with the treating physician which medications are being taken. Exercise Another factor that influences blood sugar levels is the amount of energy you use. During gentle, regular exercise, the regular release of a small amount of glucose from reserve stores is sufficient. Great efforts in a short time also require a lot of energy in a short time. It is then difficult for the body to maintain blood sugar levels.
Stress and antihormones
Stress also plays an important role in blood sugar levels. When stressed, the stress hormones adrenaline and cortisol are always produced. As discussed earlier in this chapter, a lot of glucose is then released, so that a lot of energy is available and blood sugar levels become high. In many cases of stress, this large amount of energy is not necessary, and in an argument with someone there is often no flight or fight. The body is therefore stimulated by the high blood sugar level and, in response, produces antihormones to lower the blood sugar level. These antihormones often cause blood sugar levels to become too low, causing people to feel tired and weak again. In response to this, people will eat something with a high GI, which in turn causes a rapid rise in blood sugar levels. The body then produces antihormones again. This leads to a vicious circle.
Disease
When people are sick, this also affects blood sugar levels. For example, when you have a cold, the body responds by producing hormones that increase your blood sugar level. In case of illness, extra energy is needed, for example for the production of antibodies against the disease. Finally, there is a factor that only matters to women. This is the fluctuation in hormone levels during the menstrual cycle. Due to the changed production of hormones, blood sugar levels can also fluctuate. This mainly happens in the week before menstruation or during menopause.
