What Is Lactate and What Does It Do in the Body?

Lactate is a molecule produced naturally within the human body, serving various roles in metabolism and energy production. Often misunderstood as solely linked to intense physical exertion or adverse health conditions, lactate is a normal and beneficial compound. It is continuously produced and utilized by cells, playing a part in the body’s daily functions even at rest.

Understanding Lactate: What It Is and How It’s Made

Lactate is generated when the body breaks down carbohydrates for energy, especially when oxygen is limited. This process, anaerobic glycolysis, occurs primarily in muscle cells and red blood cells, which lack mitochondria. During anaerobic glycolysis, glucose converts to pyruvate, which then transforms into lactate when oxygen is scarce, sustaining energy production.

It is important to distinguish between “lactic acid” and “lactate.” Though “lactic acid” is often used, lactate is the form predominantly found in the body. Lactic acid quickly dissociates into lactate and hydrogen ions (H+) at physiological pH levels. Lactate is constantly produced, even at rest, with normal blood concentrations ranging from 0.5 to 2.2 millimoles per liter (mmol/L).

Lactate’s Role in Everyday Function

Beyond intense activity, lactate serves as a fuel source for various tissues, even during non-strenuous activities. The heart, brain, and non-exercising muscles readily use lactate for energy. The liver and kidneys process lactate, converting it back into glucose through gluconeogenesis, a metabolic pathway known as the Cori cycle.

Lactate is a dynamic metabolite, not merely a waste product. It acts as a carbon source shared by different tissues for oxidation, facilitating inter-organ energy exchange. This constant turnover ensures lactate is efficiently managed and repurposed, contributing to metabolic balance.

Lactate and Exercise Performance

Lactate production increases with exercise intensity, especially during high-intensity activities like sprinting or weightlifting. Historically linked to muscle fatigue and the “burning sensation,” recent research shows lactate is not the direct cause of fatigue. Instead, it serves as a fuel source for muscles and can delay fatigue. The burning sensation is more closely linked to hydrogen ion accumulation, which lowers pH.

The “lactate threshold” represents the exercise intensity where lactate accumulates in the bloodstream faster than the body can remove it. Training at or near this threshold improves endurance performance, allowing athletes to sustain higher intensities longer. Regular endurance exercise enhances the body’s ability to clear lactate more efficiently, increasing mitochondrial capacity and lactate transporters in muscle fibers.

When High Lactate Signals a Problem

While lactate is normal, abnormally high levels, known as lactic acidosis, indicate a serious health issue. Lactic acidosis occurs when lactate production exceeds the body’s clearance ability, causing a blood pH imbalance. This can develop rapidly or gradually.

Elevated lactate levels can stem from various medical conditions. Common causes include severe infections like sepsis, inadequate oxygen delivery to tissues (e.g., shock), and organ failures (especially liver or kidney dysfunction). Certain medications, including some for HIV or diabetes, can also contribute. Symptoms may include nausea, vomiting, exhaustion, rapid or shallow breathing, and muscle cramps. These symptoms warrant immediate medical attention, as untreated lactic acidosis can lead to severe complications and be life-threatening.