16-OH-E1, or 16-hydroxyestrone, is a naturally occurring estrogen metabolite found in the human body. It is formed through the metabolism of estrone, one of the three primary estrogen hormones produced in the ovaries of females and in smaller quantities in the testes of males.

Estrogens, including 16-OH-E1, play crucial roles in regulating various physiological processes, including the development of secondary sexual characteristics, menstrual cycle regulation, and maintenance of bone density. They also influence the growth and function of reproductive tissues.

The "16-OH" in 16-OH-E1 indicates the presence of a hydroxyl group (OH) on the sixteenth carbon of the estrogen molecule. Different estrogen metabolites, like 16-OH-E1, can have varying effects on the body and may be linked to different health outcomes. These metabolites can also serve as biomarkers in medical research and clinical practice to study estrogen metabolism and its potential implications for health.

Understanding the balance and levels of various estrogen metabolites is important in the context of hormone-related conditions and diseases, including breast cancer, as it can provide insights into estrogen metabolism and its potential role in disease development or progression.