Katherine Wynne-Edwards
Queen's University

From fatherhood to breast cancer prevention: Hormone dynamic indices as a link between lifestyle and the endocrine system

In endocrinology, the y-axis is always hormone concentration. However, cells respond to changes in concentration rather than calibrating their responses to absolute hormone concentration. As a result, two individuals with the same average hormone concentration will differ profoundly in their cellular physiology if they differ in the extent of variation surrounding that mean. We call this variation the dynamic index. Over recent years, we have noted cases in which critical biological events (such as new parenthood) are associated with changes in dynamic index but not mean. More recently, we have shown that the dynamic index has at least a three-fold range across individual men, women, and dwarf hamsters, when measured as testosterone, DHEA, progesterone, or cortisol. We have also found that the dynamic index for testosterone (total or free) in male hamsters is reversibly altered by diet and exercise, and these experiments support associations between diet, exercise, and sex steroid dynamic indices that we have found in adolescent girls. As such, dynamic indices are plausible biological mechanisms through which individual differences in lifestyle and behaviour could alter endocrine physiology and thereby influence disease risk.