Exercise does increase bilirubin levels, sometimes dramatically. A study of long-distance runners found that total serum bilirubin roughly doubled after a race, driven by a combination of red blood cell destruction and temporary changes in liver function. The size of the increase depends on how long and how hard you push yourself, and the relationship between bilirubin and physical activity turns out to be more interesting than a simple spike-and-recovery story.
Where Bilirubin Comes From in the First Place
Bilirubin is the yellow pigment your body produces when it recycles old or damaged red blood cells. The process starts with an enzyme called heme oxygenase, which breaks down heme (the iron-carrying part of hemoglobin) into a green compound called biliverdin, along with carbon monoxide and free iron. A second enzyme then converts biliverdin into bilirubin. This “unconjugated” bilirubin travels through the bloodstream to the liver, where it gets processed and eventually excreted in bile. Under normal conditions, the rate of red blood cell turnover is steady enough that bilirubin levels stay within a predictable range. Exercise disrupts that equilibrium from multiple directions at once.
How Exercise Drives Bilirubin Up
The most direct route is hemolysis, the premature destruction of red blood cells. During running, red blood cells passing through the small blood vessels in your feet get physically crushed with every footstrike. Research on distance runners has confirmed that this mechanical trauma is a major cause of hemolysis during running, supported by drops in haptoglobin, a protein that mops up free hemoglobin released from damaged red cells.1PubMed. Foot impact force and intravascular hemolysis during distance running More destroyed red blood cells means more heme to break down, which means more bilirubin entering the bloodstream.
But footstrike hemolysis is not the whole picture. Intense exercise also stresses the liver. Blood flow to the liver actually decreases during vigorous exercise as the cardiovascular system redirects blood to working muscles.2PubMed. Effects of changing liver blood flow by exercise and food on kinetics and dynamics of saruplase A liver receiving less blood has a harder time processing and clearing bilirubin at its normal rate. So you end up with more bilirubin being produced at the same time the organ responsible for clearing it is temporarily working at reduced capacity. That combination is why bilirubin rises so sharply during prolonged exercise.
How Much Bilirubin Actually Rises
The magnitude of the spike depends heavily on the duration and intensity of exercise. The clearest data comes from a study of runners who completed a long-distance race. After researchers accounted for the loss of plasma volume that happens during prolonged running (which would artificially concentrate blood markers), total bilirubin was still elevated by about 106%. Unconjugated bilirubin, the form produced by hemolysis, rose by roughly 96%, while conjugated bilirubin, the form processed by the liver, increased by about 283%. A 66% drop in haptoglobin confirmed that significant red blood cell destruction had occurred. The researchers concluded that both hemolysis and hepatic disturbances contributed to the bilirubin rise.3Medicine and Science in Sports and Exercise. Effects of long-distance running on serum bilirubin
The jump in conjugated bilirubin is the telling detail. If hemolysis alone were responsible, you would expect mostly unconjugated bilirubin to rise. The outsized increase in the conjugated fraction points to the liver struggling under the stress of prolonged exercise, either producing more conjugated bilirubin than it can excrete or leaking it back into the bloodstream from overwhelmed liver cells.
Longer Races Mean Higher Bilirubin
A comparative study of runners completing three different race distances, a standard marathon, a 100-kilometer ultramarathon, and a 308-kilometer ultramarathon, showed that the bilirubin response scales with distance in a way that is not entirely intuitive. Total and direct bilirubin were significantly elevated after the 100-km and 308-km races, and the 308-km race produced the highest bilirubin levels of all three distances.4PubMed Central. Comparison of Changes in Biochemical Markers for Skeletal Muscles, Hepatic Metabolism, and Renal Function after Three Types of Long-distance Running: Observational Study
What makes this interesting is that the 308-km race is actually run at a lower intensity than the marathon. Runners simply cannot sustain marathon pace for that long, so they slow down considerably. Yet the bilirubin levels were highest in the longest race. This suggests that cumulative duration of exercise matters more than intensity per se when it comes to bilirubin production. Hours upon hours of repetitive impact and sustained metabolic stress appear to cause more hemolysis and greater hepatic disruption than a shorter, faster effort. If you are a recreational jogger doing 30 minutes a few times a week, your bilirubin probably does not move much. If you are running ultramarathons, your blood work after a race will tell a different story.
Athletes Have Higher Bilirubin at Baseline
The acute post-exercise spike is one thing, but there is also evidence that habitual training raises your resting bilirubin over time. A study comparing elite Czech athletes to the general Czech population found that athletes had significantly higher serum bilirubin even when measured at rest: 11.6 versus 9.6 micromoles per liter overall, and the difference held for both men (12.6 versus 11.3) and women (10.5 versus 8.3).5PubMed Central. Serum Bilirubin Concentrations and the Prevalence of Gilbert Syndrome in Elite Athletes A separate review of the evidence has similarly noted that plasma bilirubin levels are elevated by exercise training and that elite athletes may carry significantly higher levels than sedentary individuals.6Frontiers in Sports and Active Living. Cutting edge concepts: Does bilirubin enhance exercise performance?
The reasons for this chronic elevation are not entirely settled. Part of it could be ongoing low-grade hemolysis from daily training. Part of it might reflect adaptive changes in bilirubin metabolism. And part of it involves a genetic factor that complicates the picture considerably.
The Gilbert Syndrome Connection
Gilbert syndrome is a common, harmless genetic condition in which the liver is slightly less efficient at conjugating bilirubin. People with it tend to have mildly elevated unconjugated bilirubin, especially during fasting, stress, or illness. It affects somewhere around 5 to 10% of the general population, depending on the study. What caught researchers’ attention is that the condition appears far more often among elite athletes.
In the Czech study, 22% of elite athletes met the criteria for Gilbert syndrome, compared to about 9.6% of the general population. The athletes also showed a higher frequency of the genetic variants associated with the condition.5PubMed Central. Serum Bilirubin Concentrations and the Prevalence of Gilbert Syndrome in Elite Athletes A study of Italian Olympic athletes similarly identified the condition in about 6% of the cohort overall, with a strong skew toward males, where the rate was 9%. Endurance athletes in that cohort had the highest total and indirect bilirubin.7PubMed Central. Cardiovascular and metabolic effects of hyperbilirubinemia in a cohort of Italian Olympic athletes
This raises a provocative question: does mildly elevated bilirubin actually help athletic performance? The researchers behind the Czech study suggested that a mild chronic elevation in serum bilirubin might predispose people to better sports performance.5PubMed Central. Serum Bilirubin Concentrations and the Prevalence of Gilbert Syndrome in Elite Athletes Bilirubin is one of the body’s most potent naturally occurring antioxidants, and exercise generates large amounts of oxidative stress. Having a bit more antioxidant protection circulating at all times could theoretically help with recovery, reduce exercise-induced tissue damage, or improve cardiovascular function. The evidence here is still correlational rather than proven cause-and-effect, but the overrepresentation of Gilbert syndrome among top athletes across multiple independent studies is hard to dismiss as coincidence.
Sex Differences in the Bilirubin Response
Men tend to have higher bilirubin levels than women across the board, and this gap persists among athletes. In the Italian Olympic athlete cohort, male athletes had higher indirect bilirubin than female athletes (0.53 versus 0.36 milligrams per deciliter), and Gilbert syndrome was far more commonly identified in men.7PubMed Central. Cardiovascular and metabolic effects of hyperbilirubinemia in a cohort of Italian Olympic athletes The Czech data showed the same pattern, with the male athletes’ average bilirubin about 20% higher than the female athletes’ average.5PubMed Central. Serum Bilirubin Concentrations and the Prevalence of Gilbert Syndrome in Elite Athletes
Some of this is driven by hormonal differences. Estrogen influences bilirubin metabolism, and men generally have higher red blood cell mass, meaning more hemoglobin turnover and more bilirubin production at baseline. For women who exercise heavily, bilirubin levels still rise, but the starting point and the ceiling are both typically lower. This matters practically when interpreting blood test results: a “mildly elevated” bilirubin reading in a female athlete might represent a proportionally larger shift from her individual baseline than the same number would in a male athlete.
What This Means If You Get Blood Work Done After Exercise
If you exercise vigorously in the day or two before a blood draw, your bilirubin levels could easily fall outside the standard reference range. Given that a long-distance race can double total bilirubin, even a hard training session could push numbers up enough to look abnormal on a routine metabolic panel. This can trigger unnecessary concern, or even additional testing for liver disease, if the clinician interpreting the results does not know about your recent exercise history.
The practical advice is straightforward: if you are getting blood work done for any reason and your doctor does not already know about your exercise habits, mention them. Ideally, avoid intense exercise for at least 24 to 48 hours before a scheduled blood draw. The bilirubin elevation is temporary and physiologically normal in the context of exercise, but it looks identical on a lab report to the bilirubin elevation caused by actual liver or blood disorders. Knowing the context is what separates the two.
For athletes who regularly show mildly elevated bilirubin at rest, understanding whether they carry Gilbert syndrome can also be useful. The condition is easy to identify with a genetic test or a simple clinical assessment, and knowing you have it prevents years of vaguely worried follow-up appointments every time your bilirubin comes back a touch high.
Altitude Adds Another Layer
If you exercise at high altitude, you may be compounding the bilirubin effect from two directions. At higher elevations, the body responds to lower oxygen availability by ramping up red blood cell production. More red blood cells means more hemoglobin turnover and, eventually, more bilirubin. A study of newborns at different altitudes demonstrated this clearly: at 3,100 meters, 39% of newborns developed hyperbilirubinemia compared to 16% at 1,600 meters, driven by increased bilirubin production and delayed clearance.8JAMA Network. Neonatal hyperbilirubinemia at high altitude
While this study focused on neonates, the underlying physiology applies to adults as well. Your body responds to altitude by increasing erythropoietin and producing more red blood cells, a process that also increases the rate of red blood cell destruction and bilirubin production. An athlete training at altitude is therefore dealing with exercise-induced hemolysis layered on top of altitude-induced red blood cell turnover. Trail runners, mountaineers, and anyone doing altitude training camps should be aware that their bilirubin levels may run noticeably higher than they would at sea level, even without changes to training volume or intensity. This is not pathological, but it is one more reason to give your doctor the full context when lab values look off.
The Endurance Athlete Paradox
There is something genuinely counterintuitive about bilirubin’s role in exercise physiology. On one hand, exercise clearly causes red blood cell destruction and liver stress, both of which raise bilirubin. That sounds bad. On the other hand, bilirubin is a powerful antioxidant, and the athletes with the highest levels, particularly endurance athletes, appear to carry a performance advantage rather than a disadvantage. In the Italian Olympic athlete study, it was the endurance athletes specifically who had the highest total and indirect bilirubin compared to other sports.7PubMed Central. Cardiovascular and metabolic effects of hyperbilirubinemia in a cohort of Italian Olympic athletes
This fits a broader pattern in exercise science where the body’s response to a stressor becomes part of its adaptation. Exercise damages muscle fibers, but the repair process makes them stronger. Exercise depletes energy stores, but the refilling process makes them larger. Exercise raises bilirubin through hemolysis and liver stress, but the resulting antioxidant may protect against the oxidative damage that intense training generates. Whether the bilirubin elevation is a happy byproduct of training or an actual contributor to performance is still being worked out, but the correlation between high bilirubin and elite athletic status is strong enough that researchers have begun asking whether bilirubin actively enhances exercise performance rather than just tagging along as a marker of exertion.6Frontiers in Sports and Active Living. Cutting edge concepts: Does bilirubin enhance exercise performance?
For now, the evidence sits at an intriguing-but-unproven stage. Nobody is suggesting you should try to raise your bilirubin on purpose. But if you are an active person whose lab results consistently show bilirubin at the upper end of normal or slightly above, the emerging science suggests that this is not something to worry about. It may, in fact, be a sign that your body is doing exactly what regular exercise has trained it to do.