Lactate is an organic molecule found in every cell, with the chemical formula C3H5O3-. It is an anion, carrying a negative charge. While often confused with “lactic acid,” which is rarely present, lactate is continuously produced and serves various functions.
Formation of Lactate
Lactate is primarily formed during glycolysis, the breakdown of glucose for energy. This metabolic pathway occurs in the cytosol. In the absence of sufficient oxygen, pyruvate is converted into lactate by an enzyme called lactate dehydrogenase (LDH). This conversion regenerates NAD+, necessary for continued ATP production via glycolysis. While lactate production increases significantly during intense exercise when oxygen supply might be limited, it is also continuously produced even at rest, as part of normal metabolic processes.
Role in Energy and Performance
Lactate plays a role as an energy source during physical activity. It can be transported to other tissues, including muscles, the heart, and the brain, where it is converted back into pyruvate and used for energy through aerobic metabolism. The liver also uses lactate to produce glucose through gluconeogenesis, replenishing blood sugar levels, especially after exercise.
A common misconception is that “lactic acid” causes muscle soreness or fatigue. However, it is primarily the accumulation of hydrogen ions that makes the muscle environment acidic, leading to the burning sensation during strenuous exercise. Lactate actually helps to buffer these hydrogen ions, reducing the acidity. Delayed onset muscle soreness (DOMS) is primarily due to microscopic tears in muscle fibers, not lactate accumulation. Lactate is a valuable metabolic intermediate, not merely a waste product, and the body efficiently clears and reuses it.
Broader Biological Roles
Beyond its role in exercise, lactate functions as a signaling molecule. It can influence gene expression and cellular communication by interacting with specific receptors, such as GPR81 and GPR132. This signaling role impacts various biological processes, including energy metabolism and inflammation.
Lactate is also important in other organs. In the brain, for instance, it serves as a fuel source for neurons and astrocytes, supporting cognitive function. The heart can also use lactate as an energy source. Lactate also plays a role in immune cell function and the metabolism of cancer cells. In tumor environments, lactate can influence immune responses and promote tumor progression by altering the metabolic crosstalk between cancer cells and immune cells.
Clinical Relevance
Lactate levels are routinely measured clinically because they provide insights into a patient’s health. A normal blood lactate level is typically between 0.5 and 1 mmol/L. Elevated lactate, known as hyperlactatemia (2-4 mmol/L) or lactic acidosis (greater than 4 mmol/L), can indicate various underlying medical conditions.
Increased lactate levels often signal impaired tissue oxygenation, resulting from decreased oxygen delivery or utilization. This can occur in conditions such as sepsis, or in shock states like cardiogenic, hypovolemic, or obstructive shock. While an elevated lactate level is an indicator of metabolic stress, it is a marker of an underlying problem, not the problem itself. Healthcare professionals use lactate measurements as a diagnostic tool to assess disease severity and guide treatment, aiming to resolve the root cause of the elevation.