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 carve 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 action by the osteoblasts. The osteoblasts are the building cells that form bone. Bone building occurs when more bone is formed than removed.
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 your family history. People who attain higher peak bone mass have larger and heavier bones and are less likely to get osteoporosis later in life.
Peak bone mass is reached between 16 and 25 years of age. In youth and young adulthood, eating a nutrient rich diet, consuming the calcium you need each day, getting the recommended amount of vitamin D, participating in regular exercise, and avoiding smoking are some of the bone healthy actions necessary to reach peak bone mass. Hormonal balance is also necessary to reach peak bone mass. It is important to have height and weight checked yearly by a healthcare provider; proper growth is a sign of hormonal balance. In females, a normal menstrual cycle is another indicator of normal hormone levels.
After peak bone mass is reached (after about age 25), bone healthy actions help maintain bone mass. If your diet is too low in calcium or you get too little vitamin D (necessary for your body to use calcium) your body will "withdraw" the calcium it needs from your bone bank. There are medical conditions and certain medications that can also cause your body to withdraw calcium 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 of osteoporosis.