The first step to bone health is understanding how bone is made. Two types of bone cells are involved in the bone-building process: osteoclasts and osteoblasts. The osteoclasts trigger bone resorption, which means to lose substance. In other words, osteoclasts are the cells that break down existing bone to make way for new bone. After the osteoclasts do their work, the osteoblasts trigger the bone building that is necessary to replace the bone that has been resorbed.
From childhood until around age 30, the osteoblasts work harder than the osteoclasts, which means more bone is built than is resorbed. Around age 30 you reach your peak bone mass, the time when your bones are as dense as they will ever be. Then the balance begins to shift. For a while the osteoclasts and the osteoblasts work pretty evenly, but around age 50 the osteoclasts (the resorbers) begin to outpace the osteoblasts (the builders), which means more bone is resorbed than is newly made. This is what causes bone density to decrease.
Peak Bone Mass
A high peak bone mass decreases the risk of osteoporosis and fractures later in life. That’s because there is more bone to lose before bone density becomes dangerously low. Genetics play a large role in determining who will have a high peak bone mass, but there are other factors as well. For example, women who played sports and ate a calcium- and vitamin D-rich diet before 30 are more likely to have a high peak bone mass than are women who smoked, didn’t exercise, didn’t have a good diet, or had an eating disorder.
Some women begin losing bone before menopause, others have a considerable decrease when they reach menopause, and others lose comparatively little at that time. About 35% of women lose a significant amount of bone with menopause. Women who have had their ovaries removed before age 35, or who enter menopause due to treatments for breast cancer that shut down the ovaries, appear to lose bone more quickly and are more likely to develop osteoporosis than are women who have had a natural menopause. This is because the ovaries, in addition to producing estrogen and progesterone, produce testosterone, which helps to maintain bone density.