Osteoporosis and osteopenia (a less severe form of low bone density) can affect people of all ages but becomes more likely as we age. Women, especially post-menopausal women, have the greatest risk, accounting for about 80% of all cases. A rare but severe form of the disease known as pregnancy and lactation-associated osteoporosis (PLO) affects younger women, usually in the third trimester of pregnancy or during lactation.