In people’s early- to mid-20s, they reach what is called peak bone mineral density, which is higher for men than it is for women, according to researchers. This peak is one of the main determinants of fracture risk later in life. After reaching this peak, a person’s bone density remains roughly stable for a couple of decades. Then, when women enter the menopausal transition, they experience accelerated bone loss. Men also experience bone density decline as they age. Sleep patterns also evolve over time.