Bilirubin, including total and direct levels, is a biomarker used in longevity research to assess liver function and overall health. Elevated levels of bilirubin can indicate liver damage or dysfunction, which may impact longevity and overall well-being. Monitoring both total and direct bilirubin levels can provide valuable insights into the risk of chronic diseases such as liver disease, cardiovascular disease, and metabolic disorders. By tracking and managing bilirubin levels, individuals and healthcare professionals can make informed decisions to support healthy aging and longevity. Additionally, bilirubin levels may be used in conjunction with other biomarkers to create a more comprehensive assessment of an individual’s health status and potential longevity.