Bone, aging peak mass

Osteoporosis is a disablirtg disorder that is characterized by decreased borte strertgth, which predisposes patients to an increased risk of bone fracture. Peak bone mass (maximum bone strength and density) is normally attained by age 20-25. Age, race, sex, environment, and lifestyle factors such as physical activity and diet are important determinants of bone density. With the increase in age, the rate at which bone tissue is replaced is reduced in comparison to the rate at which it is lost, which increases the risk for fractures. 

Under normal circumstances, the skeleton undergoes a dynamic process of bone remodeling. Bone tissue responds to stress and injury through continuous replacement and repair. This process is completed by the basic multicellular unit, which includes both osteoblasts and osteoclasts. Osteoclasts are involved with resorption or breakdown of bone and continuously create microscopic cavities in bone tissue. Osteoblasts are involved in bone formation and continuously mineralize new bone in the cavities created by osteoclasts. Until peak bone mass is achieved between the ages of 25 and 35, bone formation exceeds bone resorption for an overall increase in bone mass. Trabecular bone is more susceptible to bone remodeling in part owing to its larger surface area. 

In order to prevent certain risk factors and maximize peak bone mass, efforts must be directed toward osteoporosis prevention at an early age. 

The recommended dietary allowance, RDA, for calcium In the United States Is 800 mg per day (1) However, this amount of calcium may not be adequate throughout adult life for maintaining the normal skeletal structure and for preventing bone loss with aging, particularly In females Recent studies Indicate that this amount of calcium may not be adequate for maintaining the optimal bone mass which reaches Its peak at the age of 30 to 35 years (2) and decreases thereafter Even If the calcium Intake Is adequate, one has to consider to which extent this amount of calcium Is utilized There may be a decrease In the Intestinal absorption of calcium (3) or the... 

A lack of regular physical activity, together with a habitually low Ca intake during adolescence, interferes with the attainment of one s genetic potential for peak bone mass during the ages 19 through 30 years. 

Osteoporosis is of two forms- primary i.e. idiopathic and secondary. Primary osteoporosis is classified into type I and type II osteoporosis. Type I is referred to post menopausal osteoporosis which is the main type affecting women, characterized by rapid bone loss and affects women after the menopause, mainly in trabecular bone and is associated with vertebrae and distal radio fractures whereas type II also termed as senile osteoporosis occurs due to chronic deficiency of calcium, increase in parathormone activity and decrease in bone formation and is associated with aging. On the other hand secondary type results from inflammatory processes, endocrine changes, multiple myeloma, sedentariness and the use of drugs such as heparin, corticoid and alcohol [3]. Prevention is the main treatment of osteoporosis, for which bone mass peak and the prevention of postmenopausal reabsorption are critical elements. The common treatment of osteoporosis includes calcium consumption as calcium salts, vitamin D supplements, and hormone reposition [4], the use of calcitonin to modulate serum levels of calcium and phosphorous [5], the use of bisphosphonate, mainly alendronates [6], use of ipriflavone and sodium fluoride [7], besides physical activity to strengthen muscles, stimulate osteoblasts formation and prevent reabsorption. 

The skeleton undergoes constant remodeling throughout life. Peak bone mass is achieved by age 20 to 30 years, long after maximum bone length has been achieved. Men achieve higher peak bone mass than women. For 5 to 10 years after menopause, women have accelerated bone loss, up to 3% per year. Age-related bone loss, about 0.5% per year, begins 10 to 15 years after menopause in women and in men at about age 55 years. ... 

The goal from birth to around 20 to 30 years of age is to achieve the highest peak bone mass as possible. Beyond this age, the goals are to maintain BMD and minimize age-related and postmenopausal bone loss. In women and men with osteopenia, prevention of osteoporosis is the goal. For a variety of reasons, osteoporosis prevention is not always possible. For those at significant risk of developing an osteoporosis-related fracture, the aims are to increase bone mineral density, prevent further bone loss, and to prevent falls and fractures and their associated sequelae. For those who experience an osteoporosis-related fracture, the goals are to achieve adequate pain control, maximize rehahihtation... 

Although predominantly attributed to hypoestrogenemia, diet has a significant impact, since BMD is lower in those with amenorrhea from anorexia than in those whose conditions result from excessive exercise. Anorexia s effect is greatest if it occurs before peak bone mass achievement. After 6 months of amenorrhea, a bone density test should be performed and then repeated yearly while amenorrheic. BMD measurements may be inaccurate in small-boned people and children, requiring the use of Z-scores, especially before peak bone mass achievement, or corrections for age and sexual maturity. For those with amenorrhea or anorexia, higher calcium intakes of 1200 to 1500 mg and adequate vitamin D are recommended. 

In general, peak bone mass occurs between 30 and 40 years of age (3,6) and is dependent on genetic factors as well as proper intake of calcium, maintenance of quality nutrition, and participation in weight-bearing exercise (6). Thereafter, peak bone mass progressively declines at the rate of 0.3 to 0.5% of cortical bone per year (3). After menopause, bone loss is accelerated (2% per year in the spine) (6) for a period of 5 to 10 years because of the loss of estrogen. This can result in up to a 30% decrease in bone mineral density. 

Osteoporosis is a progressive loss of bone with increasing age, after the peak bone mass is achieved at the age of about 30. The cause is the normal process of bone turnover with reduced replacement of the tissue which has been broken down (section 11.3.3.1). Both mineral and the organic matrix of bone are lost in osteoporosis, unlike osteomalacia (section 11.3.4), in which there is loss of bone mineral but the organic matrix is unaffected. 

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