Why does it occur?

Bone is a living and growing tissue. Throughout life, bone is constantly being renewed in a process called remodeling. The remodeling process is complex but includes two main types of cells, osteoclasts and osteoblasts.

Osteoclasts are bone chewing cells that remove old bone and get the bone ready for renewal. Osteoclasts release enzymes and acids that chew bones. In this process calcium, phosphorus, and other components of the bone are released into the blood for use by the body. After the osteoclasts carve the bone, it is prepared for the osteoblasts. The osteoblasts are the cells that build bone.

Bone building occurs when more bone is laid down than removed. Bone mass is maintained when bone formation equals bone removal. Bone loss occurs when more bone is removed than replaced.

Think of your bones as a bank account in which you "deposit" and "withdraw" calcium throughout life. Calcium is a mineral that makes bone dense (thick) and strong. During childhood, the teen years and early adulthood you build your bone bank. The skeleton grows and bones become larger, denser, and stronger especially when you practice bone healthy actions.

Bone grows fastest between the ages of 9 and 18 years of age. Peak bone mass, defined as the maximum bone density you will ever have, is largely determined by genetics. Peak bone mass is reached between 16 and 25 years of age. In youth and young adulthood, maintaining hormonal balance, eating a nutrient rich diet, consuming enough calcium each day, getting enough vitamin D, participating in regular exercise and avoiding smoking are some of the bone healthy actions necessary to reach peak bone mass.

People who attain higher peak bone mass have larger and heavier bones and are less likely to get osteoporosis later in life. After about age 25, bone healthy actions help maintain bone mass. Throughout your life, if your diet is too low in calcium, your body will "withdraw" the calcium it needs from your bone bank. Over time, if more calcium is taken out of your bones than is put in, the result may be thinner, weaker bones, increasing your risk for osteoporosis.