Glucose: the fuel that feeds the cells, but its excess is no good

Glucose is a type of sugar that cells use for immediate energy, making it the body's main fuel source.

Once glucose enters the cells, it gets phosphorylated and transformed into glucose-6-phosphate. This compound then goes through a series of biochemical reactions in a process called glycolysis, which results in the production of pyruvate. Pyruvate can either be fermented through lactic fermentation to produce lactate or converted into acetyl-CoA to enter the Krebs cycle. Both pathways allow cells to generate energy in the form of adenosine triphosphate (ATP), but the Krebs cycle produces significantly more ATP than lactic fermentation. Additionally, the liver can create glucose from lactate through gluconeogenesis. Some organs and tissues can also store glucose by linking its molecules together to form a polymer known as glycogen, with the process of creating glycogen called glycogenesis. When needed, glycogen can be broken down to release stored glucose through glycogenolysis.

Insulin is the hormone that regulates the entire glucose metabolism process. Produced by beta cells in the pancreas, insulin has several key functions:

• Facilitating the entry of glucose into cells
• Encouraging glycolysis
• Supporting glycogenesis
• Promoting protein synthesis
• Stimulating lipid synthesis
• Inhibiting gluconeogenesis
• Preventing protein breakdown

Disruptions in glucose metabolism can lead to various diseases, with diabetes being the most notable. Diabetes occurs when there is an excess of glucose in the blood. There are two primary types of diabetes:

• Type 1 diabetes mellitus: this autoimmune condition occurs when the immune system attacks and destroys the pancreatic beta cells, leading to a significant drop in insulin production and a rapid rise in blood glucose levels.
• Type 2 diabetes mellitus: is closely linked to obesity. In this condition, cells become less responsive to insulin, resulting in insulin resistance and causing glucose to build up in the bloodstream. At first, the pancreatic beta cells compensate by producing extra insulin to manage glucose levels. However, as the disease advances, glucose levels can rise to a point where the amount of insulin produced is no longer sufficient. If insulin resistance isn't addressed promptly, it can lead to prediabetes and eventually to type 2 diabetes mellitus, where insulin production fails to adequately control glucose levels. While the progression of type 2 diabetes is generally slower than that of type 1, its prevalence is significantly higher and more concerning due to the global rise in overweight and obesity.

Both high and low blood glucose levels are considered abnormal results. The following conditions can be established:

• Hypoglycemia: this refers to blood glucose levels that are lower than normal. In non-diabetic individuals, hypoglycemia is diagnosed when levels drop below 55 mg/dL.
• Normoglycemia: this indicates that blood glucose levels are within the normal range.
• Hyperglycemia: this condition is characterized by blood glucose levels that are higher than normal. Levels between 100 and 125 mg/dL suggest prediabetes, while levels above 126 mg/dL indicate diabetes.

Hypoglycemia can be a serious condition marked by low blood glucose levels. It is often seen in diabetic patients who may be receiving too much treatment to manage their blood glucose, but it can also occur in those without diabetes. Certain disorders affecting the liver, kidneys, and hormones, as well as the use of specific medications, can also lead to hypoglycemia. Common symptoms of hypoglycemia include:

• Restlessness
• Sweating
• Nervousness or anxiety
• Irritability or confusion
• Dizziness
• Hunger

Hypoglycemia requires immediate attention, as prolonged episodes can result in more severe symptoms, including coma and even death.

Conversely, hyperglycemia is diagnosed when blood glucose levels are elevated, often indicating prediabetes or diabetes mellitus. In some instances, other conditions affecting the pancreas or adrenal glands (among other organs) can also lead to hyperglycemia. The most common symptoms of hyperglycemia include:

• Thirst
• Fatigue and weakness
• Headaches
• Frequent urination
• Blurry vision.

The glucose test measures the levels of glucose in the blood. Generally, results below 55 mg/dL indicate hypoglycemia, while levels above 100 mg/dL are usually classified as hyperglycemia. Furthermore, results exceeding 125 mg/dL are often seen as a sign of diabetes.

However, glucose levels alone do not provide a full diagnosis of any disease and typically require additional tests for a comprehensive assessment. One of the most common tests is glycated hemoglobin (HbA1c), which reflects the amount of glucose that has attached to hemoglobin over time. HbA1c is a reliable indicator of average blood glucose levels over the past few months and is crucial for diagnosing diabetes. In addition to HbA1c, other tests are frequently performed to evaluate the severity of the disease and its potential complications, such as metabolic syndrome or effects on kidney function. These tests may include:

• Serum and urine creatinine
• Urinary albumin
• Total cholesterol
• HDL cholesterol
• LDL cholesterol
• Triglycerides
• Urinalysis.