Exercise may increase bilirubin levels because of elevated heme catabolism caused by a higher core temperature and oxidative stress, according to a study published on National Center for Biotechnology Information. Heme is the precursor to bilirubin, and thus this mechanism provides an influx of reactants to spur on bilirubin production.
When running, the heel strike of every stride can contribute to this hemolysis as well, reports National Center for Biotechnology Information. Another mechanism proposed by the researchers is through the heme-oxygenase-1 pathway. Aerobic exercise elevates the activity of HO-1, which is the rate-limiting enzyme in the conversion of biliverdin to bilirubin. Exercise improves insulin sensitivity, while insulin resistance has a limiting effect on HO-1. Thus exercise may increase HO-1 activity and bilirubin production through improving insulin sensitivity.
The study published on National Center for Biotechnology Information determined that individuals with the highest amount of insulin resistance also produced the highest amount of bilirubin after exercise. The scientists also determined that insulin-resistant individuals produced the highest amount of bilirubin when exercising at 150 percent of recommended levels. Both insulin resistance and low resting bilirubin levels are clinical signs of metabolic syndrome. Other studies have found that elevated bilirubin levels are correlated with lowered insulin usage and favorable changes in fasting blood sugar levels in diabetic women.