Test #1

Factors affecting the development of PEAK BONE MASS

-Mechanical -Nutrition -Adequate hormone levels -Genetic makeup

FACTORS INFLUENCING BONE HEALTH

Bone health is determined largely by the attainment of peak bone mass and mineral density and the rate of bone loss. Both of the processes are influenced by age and gender. Age-Related Changes in Bone Bone is a dynamic tissue that changes in density throughout its life. There exists a characteristic pattern between bone mass and age for males and females. Approximately the first 20 years of life are characterized by active growth in bone mass. Most females by the age of 18 and most males by the age of 20 have amassed 85-90% of bone mineral content. The skeletal consolidation phase occurs during early adulthood, and this the time when peak bone mass occurs. Peak bone mass is typically attained between ages 30-35. During this entire time, osteoblastic activity outweighs osteoclastic activity to yield a net gain of bone. Shortly after the attainment of peak bone mass, a loss of bone mass begins. Following the rapid-loss phase, the rate bone loss decreases. Peak bone mass will typically decline by about 2% each year but can be as much as 6% post menopause. During this time, osteoclastic activity outweighs osteoblastic activity to yield a net loss of bone. Gender Differences in Bone Mineral Density Bone mineral density changes throughout the live span for both sexes. Bone mineral density increases throughout childhood and early adult life for males and females; however, the peak bone mineral density achieved by females is less than that achieved by males. Additionally, at the time of menopause women lose the protective influence of estrogen, and the rate of bone loss is accelerated if estrogen is not pharmacologically replaced. The loss of the protective influence of estrogen explains the prevalence of osteoporotic fractures in women. Research demonstrates that women can lose up to 20% of their bone mass in the first 5-7 years post-menopause. Development of Peak Bone Mass and Mineral Density Peak bone mass and mineral density are developed during young adulthood and is influenced by mechanical factors, nutrition, hormonal levels. and genetics. The mechanical factors affecting bone are physical activity and gravity. These forces are generally accepted as necessary stimuli for bone formation and growth. Children and adolescents should be encouraged to engage in physical activity to promote bone health as well as to promote other positive changes and development within the bone. Specifically, children and adolescents should be encouraged to participate in high-impact activities for bone development. Adequate nutrition is necessary in order to develop a strong skeletal system. A nutrient that is essential to bone health, and often deficient, is calcium. Optimal daily calcium intake for adults ranges from 1000-1500 mg per day, depending on age, gender, and pregnancy or nursing. Keep in mind, however, that the absorption of calcium varies in people; an individual may be ingesting adequate levels of calcium, however, that individual may not be absorbing adequate levels to maintain bone health. Vitamin C - required for collagen synthesis. Vitamin A - stimulates osteoblastic activity. Vitamin D - increases calcium absorption. Vitamins K and B12 - necessary for bone synthesis. Adequate hormone levels - estrogen, testosterone and growth hormone are also needed to attain peak bone mass. Thus, athletes who are amenorrheic are likely to develop a lower peak bone mass than athletes with normal menstrual function. Finally, genetic makeup is an important determinant of BMD. In other words, there are genetically determined limits to the amount of BMD that an individual can attain. But the only way to achieve genetic potential is to pay careful attention to the factors than an individual can modify, namely nutritional status, hormonal status, and activity level.

Bone remodeling

Bone tissue, also called osseous tissue, is a dynamic, living tissue that is constantly undergoing change. 10-30% of an adult's skeleton and 100% of an infant's skeleton is typically replaced each year by the process of bone remodeling. Bone remodeling => refers to the continual process of bone breakdown (resorption) and formation (deposition of new bone). Bone remodeling plays an important role in regulating blood calcium levels and in replacing old bone with new bone to ensure the integrity of the skeletal system. The mass and shape of the bones depend largely upon the stress placed upon them. The more the bones are stressed (by mechanical loading in the form of activity), the more they increase in volume and mass, specifically at the site of mechanical loading. Hormones play a critical role in bone remodeling. If blood levels of calcium drop below normal values, parathyroid hormone stimulates osteoclast activity, causing calcium to be released from its storage site, the skeletal system. Excess calcium in the blood leads to the release of calcitonin (from the thyroid gland), which causes deposition of calcium in the bone. This deposition has the effect of decreasing blood calcium levels and simultaneously increasing bone mineral density. Other hormones that play an important role skeletal health are the sex steroids (estrogen and testosterone) and growth hormone. These hormones stimulate the protein formation necessary for bone growth and are responsible for the closure of the epiphyseal plate, which will ultimately determine bone length and thus a person's height. Estrogen is important in promoting calcium retention and acts as an inhibiting agent of parathyroid hormone. The loss of the protective role of estrogen on the skeletal system has important consequences for women after menopause or during secondary amenorrhea (absence of menses). A decrease in estrogen has the net result of increasing bone resorption. Also, decreased testosteron in males, especially by about age 65, is linked to the development of osteoporosis. Hormones are themselves stimulated by other factors, including physical activity.

ASSESSMENT OF BONE HEALTH

Measures of bone mass and bone mineral density are used to describe bone health. Bone mass is the overall quantity of bone. Bone mineral content refers to the absolute amount of hydroxyapatite - calcium and phosphate salts that are responsible for the hardness of the bone matrix - measured in grams. While bone mass can be thought of as the quantity of bone, the bone, the mineral density can be thought of the as the "quality" of that same bone. *Because a large portion of the bone mass is the mineral density, these terms are often not distinguished. Bone mineral density is defined as the relative value of bone mineral per measured bone area, expressed as grams per centimeter squared or milligrams per centimeter cubed. Bone mineral density is used clinically to provide an operational definition of osteopenia and osteoporosis.

Osteoporosis

Osteoporosis is a condition characterized by a loss of mineral bone density, resulting in bones that are weak and susceptible to fracture. This disease represents an imbalance between bone resorption and bone formation: resorption occurs faster than formation, leading to a decrease in bone mineral density. Osteoporosis=> is a condition of porosity and decreased BMD that is defined as BMD greater than 2.5 standard deviations below values for young, normal adults. Established osteoporosis refers to the condition of osteoporosis as defined, and one or more fractures.