Serum cortisol is a biomarker that is often used in longevity research. It is a hormone produced by the adrenal glands in response to stress, and chronically elevated levels of cortisol have been associated with a range of age-related health issues such as obesity, diabetes, and cognitive decline. Monitoring serum cortisol levels can provide valuable insight into an individual’s stress response and potential risk for age-related diseases. By understanding and managing cortisol levels, researchers and healthcare professionals can potentially improve an individual’s overall health and wellness, contributing to a longer and healthier lifespan.