Estrogens and progestins

Osteoporosis remains a significant public health issue, with the number of people who suffer from this age-related disease increasing concomitantly with the increase in human life expectancy. This disease is characterized by low bone mass which eventually can lead to increased susceptibility to fracture. Seminal studies conducted by Fuller Albright in the 1940s provided the original description of estrogen deficiency as a major trigger for age-related bone loss, and studies by Jensen and Gorski in the 1960s moved this understanding into the molecular realm by correctly suggesting that receptors exist that mediate many of the effects of exogenous estrogens. By comparison, the roles of progestins in bone biology are considerably less well understood. This review will focus on our current knowledge on the functions of both estrogen and progestins on bone physiology based on mouse and human studies. Since this subject has been extensively reviewed elsewhere, including in great detail in the third edition of this book in 2008, the current review will briefly summarize well-established knowledge with a greater focus on new progress made in the past decade.