Peak Bone Mass - The Basics Of Bone: Osteoporosis

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Peak bone mass

During the first 20 years of life, new bone is built more quickly than old bone is removed. By the late teens, most bone formation has already occurred. By age 20, most women have already built 98% of their skeletal mass, and by age 30 most men and women reach their peak bone mass.

Subsequently, among women, bone mass remains level until the onset of menopause, when bone is lost rapidly. While the pace of bone loss slows after the first few years of menopause, women continue to lose bone. In the five to seven years after menopause, women can lose up to one-fifth of their bone mass. Bone loss usually begins later for men — most often, when they are in their 50s — and it progresses more slowly. But by ages 65–70, most men and women lose bone at the same rate.

Peak bone mass varies from person to person. Heredity, lifestyle, state of health, and estrogen levels all play important roles in determining how much bone you'll have in the bank when heavy withdrawals begin. It's important to begin growing this "rainy day fund" early, when you have the most opportunity to influence your bone mass. Building up your bones in your teens pays hefty dividends later in life.

Here are some of the factors that can influence your peak bone mass:

Inherited traits. Sex, race, and genetics help determine peak bone density. As a rule, bone density is 30% higher in men than in women and 10% higher in blacks than in whites. Even so, there is a wide variation within these groups. The difference may be due to the work of several genes that determine bone mass, bone turnover, and bone loss.

Diet. What you eat early in life has a lot to do with the state of your bones later on. Research indicates that women whose diets contain the greatest amounts of calcium and vitamin D during childhood and adolescence have denser bones during adulthood. Consuming enough calories is also vital: When girls and women have too little body fat to support menstruation because of anorexia or bulimia, their bones suffer and they are in greater jeopardy of developing osteoporosis.

Exercise. Regular weight-bearing exercise during your early years contributes to peak bone density. This includes any activities that involve overcoming gravity's pull — not just weightlifting, but also running, walking, aerobics, soccer, basketball, gymnastics, tennis, golf, or comparable forms of exercise. Exercise puts stress on bone, and bones respond by toughening up — in this case, by adding tissue through formation. However, exercising to the extreme, which is increasingly common among young dancers, long-distance runners, and gymnasts, can result in declining estrogen levels, amenorrhea (abnormal absence of menstrual periods), and eventually bone loss.

Medical conditions. Certain chronic disorders that result in excessive resorption can reduce peak bone mass (see "Possible causes of secondary osteoporosis"). Some common culprits include hyperthyroidism, certain cancers, chronic liver disease, rheumatoid arthritis, and malabsorptive disorders (conditions that develop because nutrients from food aren't being absorbed into the bloodstream properly).

Certain medications. Some drugs can also lead to bone loss (see "Possible causes of secondary osteoporosis"). One is too much thyroid hormone taken as therapy for an underactive thyroid gland. Others include glucocorticoids, which are taken to control asthma, immune disorders, and other diseases (see "Six ways glucocorticoids hinder bone formation"). Also, because several drugs that speed bone loss are commonly given after organ transplants, people who have had these operations are at considerable risk of developing osteoporosis.

Last updated:	January 23, 2007