The Benefits of Physical Activity in the Prevention of Osteoporosis

Introduction

Osteoporosis is an important public health concern especially in today’s health-oriented era. The growing number of those affected by osteoporosis has led to a growing concern in health care circles about the disease that has been called, “the hidden epidemic.” As, the increasing proportion of the elderly population, the disease is expected to increase dramatically in the next 50 years, predicting fracture rates at 650,000 by year 2050 (Barrett-Conner, 1995).

This disease is a major health concern affecting 44 million people in the United States, eighty percent of who are women (NIH Consensus, 2001). Medical costs for osteoporosis are estimated to total between $10 and $15 billion each year and the cost is expected to increase to more than $60 billion by the year 2020. By the age of 65, only one in women will have normal bone mass and one in three will have osteoporosis.

            The National Osteoporosis Foundation defines osteoporosis as “a disease characterized by low bone mass structural deterioration of bone tissue, leading to bone fragility and an increases susceptibility to fractures of the hip, spine, and wrist” (Wellness & Prevention Sourcebook, 1998, p.179). It is possible to be completely unaware of the presence of low bone mass and concomitant increased risk of fracture until a fall or even a minor trauma causes a bone to break. The collapse of vertebra can produce pain during the acute event, which may resolve or become chronic. Vertebra fractures often result in severe kyphosis, or dowager’s hump, and accompanying abdominal organ compression and gastrointestinal disturbances.

            Despite the prevalence of this condition many remain unaware or unconvinced of the steps for the prevention of osteoporosis. Thus, the purpose of this paper is to make awareness of the benefits of physical activity for the prevention of osteoporosis. For purposes of this research, the terms physical activity and exercise are used interchangeably.

Review of Related Literature

            Several studies have found positive relationship between physical activity and bone density ( Kriska et al, 1988). These studies found significant effects of physical activity (walking, running, aerobics and physical conditioning) on bone mass density of the spine. They concluded that exercise in women over 50 can be effective at preventing bone loss at the spine. In meta-analysis in 1999 of randomized control trails and non-randomized control trials, researchers examined the effect of exercise training on boss mass of the lumbar spine and femoral neck in women. They concluded 25 studies from 1966-1996. They found that in randomized control trials, exercise training programs prevented or reversed almost 1% of bone loss per year in the lumbar spine and femoral neck for women (Wolff, VanCroonenburg, Kemper, Kostense & Twisk, 1999).

            In a study of ex-athletes compared with non-athletes, researchers found that the ex-athletes had higher bone mass densities even after up to 40 years from their athlete activities. When compared to a control group of non-athletes who also started an hour or more a week vigorous activity, the ex-athletes and not the control group showed increases in bone mass (Etherington et al., 1996). Researchers examined nature females (42-50) with a history of sports training, types of previous training and bone mass density. Types of exercise were divided into 3 groups: high impact (netball, basketball), medium-impact (running, firld hockey), and non-impact (swimming) activity groups and compared them with a nonsport control group. They found that the high impact group had increases whole body bone mass density and regional leg bone mass density compared to non-impact and control groups. Regional arm bone mass density was significantly greater in all exercise groups over the control group. They concluded that female who exercise regularly high-impact activities have higher bone mass density than non-active controls.

            Studies have also examined the optional time to begin an exercise program to prevent osteoporosis. A study of evaluating exercise in pre-menopausal and postmenopausal women was done by Bussey, Rothwell, Littlewood, and Pye (1998). The effect of vertical jumping (50 jumps, 6 times weekly) on bone mass density of pre-menopausal women was studied. After 5 months, the bone mass density of the femur in pre-menopausal women increases significantly compared to a control group. After 12 months and 18 months, there was no significant difference between postmenopausal exercise groups compared to control group.

As evident in the research reviewed, bone mass can be enhanced by exercise. It is well documented that the behavioral changes of exercise can have a positive impact on preserving bone mass and thus influencing the onset of osteoporosis.

The Research

Osteoporosis: Aging and Bone Loss

            Loss of bone with aging is an inevitable process that may result in osteoporosis (Kramer and Osis, 1982). Peak bone mass is important to determine how much bone is available to be lost in aging process. The factors that regulate the amount of bone loss are mechanical loading (physical activity), nutritional status (calcium), hormonal status (estrogen), parathyroid hormone, and structural errors which occur during remodeling.

            Bone loss begins at a slow rate in the third or fourth decade of life. It then accelerates around menopause in female and slows again later in life (Aloia, 1981). At approximately 40 years of age, bone formation fails to compensate for bone porosity. This implies uncoupling of the phase of remodeling with an increase in resorption over formation. When this uncoupling occurs, an increase in bone turnover leads to an increase in bone loss. Therefore, bone loss is viewed to be a problem of bone remodeling which creates a negative bone balance at individual turnover sites.

            The strength of bone is associated with the mass or density of the bone. Changes in strength with aging are comparable to the amount of bone quantity . Therefore, a decrease in bone mass with aging is indicative of a decrease in bone strength. This decrease in strength leads to a susceptibility to fracture occurrence. Bone loss occurs in all bones, but it occurs at different parts of the skeleton and even different parts of that bone (Wahner, 1984). With aging, bone erodes erodes from within at the endosteal envelope because of bone resportion, while deposition is occurring at a slower rate at the periosteal surface (Wahner, 1984). This results in a thinning of the cortex, an increase in the external diameter of bone, and an enlargement of the modullary canal (Wahner, 1984).

Osteoporosis: Risk Factors

            The risk factors for any disease are simply those factors which increase your risk for developing that disease.

            Being a woman is the most important risk factor for getting osteoporosis. This is due to the reduction of estrogen levels following menopause. The susceptibility of osteoporosis is greater among white oriented females, whose bone turnover rate is faster, than it is for black females. In black females, resorption does not greatly overcome formation due to slower bone turnover rate.

            Other important factors are weight, physical activity (exercise) and diet. The body structure of a heavier individual puts a higher stress on bone with weight bearing, than does a slender individual with a small frame. Stress on bone causes a stimulation of bone activity, therefore increasing bone formation. Women of a slender, small stature have less stimulation of bone formation thereby increasingly their risk for developing osteoporosis.  This does not necessarily mean that overweight is healthier, but rather that small framed women are at a greater risk for developing osteoporosis.

            Alcoholics may also be susceptible to osteoporosis. People who ingest ethanol for a prolonged period of time show depress bone formation. Alcoholics who begin at adolescent depress bone formation while it is at its peak for growth. This results in a decrease in peak bone mass. When this occurs, there is a reduced amount of bone mass prior to the aging process. This greatly increases the likelihood of an occurrence of osteoporosis.

            Any one of these factors can contribute to the development of osteoporosis. Chances increase greatly in individuals having more than one of these high risk categories need to consider a change in lifestyle to reduce such risk factors. Since one cannot remove all of the risk factors from their lives, it is important to reduce as many of the factors as possible. Reducing risk factors will lessen the chance for developing osteoporosis.

            Physical activity plays a role in the development of osteoporosis in the same sense as body structure. The greater the physical activity one engages in, the greater the stress put on the skeleton, which in turn will stimulate bone formation. Women who leads a sedentary life style are more susceptible to developing osteoporosis since they do not stimulate bone growth with stress to bone.

Physical Activity: Prevention of Osteoporosis

            Osteoporosis is a disease that is far easier to prevent than treat. This is true because much of the deformity, such as that from a crush fracture, is irreversible, and because fractures set up a continue cycle of pain, decreased physical activity, further bone loss and therefore, exaggerate fragility.

            Physical activity has been studied for a preventative mechanism against osteoporosis. Bone is a dynamic tissue and its capable of adapting to the stresses imposed on it . Bone tissue responds to the forces of gravity and muscle contraction. Therefore, weight-bearing exercise may be helpful in the prevention of osteoporosis.

Immobilization in plaster, bed rest, and a weightless state all show an increase in calcium loss which when continue for a few months leads to demineralization of the lower extremities and bone atrophy. A decrease in physical activity not only decreases calcium in the body but also decreases nitrogen. This deterirration in nitrogen of bone atrophy and muscle atrophy results in a decline of mechanical strength and therefore an increase risk for fracture occurrence.

A voluntary failure to exercise would not be the only factor contributing to bone loss. Therapeutic bed rest, for whatever reason, can also be hazardous to patient. Along with impaired work performamce and casomotor instability, excessive vertebral bone loss during simple bed rest occurs as well. With a bone loss during simple bed rest occurs as well. With a bone loss of 30% the mechnical properties of the spine may be seriously comprised. Therefore, a lack of weight bearing activity causes skeletal loss.

            The basic purpose of exercise in the protection against osteoporosis is to place a tolerable stress on the skeletal system by using gravity-loading forces, as in weight –bearing , and using muscle contraction to incur a stress on the long bones of the skeleton. According Wolff’s Law: a bone becomes adapted to the functional forces acting upon it. This principle was modified by Bassett to indicated that the bone elements place or displace themselves in the direction of functional forces and increase or decrease their mass to accommodate for the stress placed on them . This mass accumulation or deterioration, therefore, reflects the amount of functional force being placed on the skeletal system. The mechanical force being placed on bone during exercise is to stimulate osterogenic cells. The mechanism by which stress on bone is to stimulate osteoblasts involves piezoelectricity.

            Piezoelectricity is the generation of an electrical field by a regular arrangement of crystals such as the calcium phosphate crystals in bone. Physical force acting on these crystal in bone will change the electrical field and these changes may stimulate obsteoblasts. The amplitude of the changes generated in the electrical field or potential is dependent upon the rate and magnitude of the mechanical stress (Aloia, 1981). This, in turn, determines the amount of stimulation to the obsteoblasts and therefore determines the amount of bone mass produced. A change in bone mineral content is therefore an adaption to the stresses or forces put upon the bone mediated through electrical signals in response to the activity or mechanical loading places on the skeleton. Physical activity is, as a result, a stimulus to bone which plays an important role in bone hemeotasis. Increases or decreases in muscle contradiction or weight bearing cause a corresponding gain or loss in bone mass.

Conclusions

            The best way to combat osteoporosis is through prevention. Physical activity is a safe and effective method of preventing osteoporosis. Ideally, the best way to start good eating and activity habits early in life so as to attain a higher peak bone mass or bone “bank account.” When involution bone loss begins, the rate can be slowed again through good nutrition and regular exercise. Typically, osteoporosis either have had low peak bone masses or are rapid bone losers. Physical activity provides effective and complementary mode of osteoporosis prevention. Thus, physical activity plays an important role in the prevention of osteoporosis.

References

Aloia, J.F(1981). Exercise and Skeletal Health, Journal of American Geriatrics Society, 29(3):   104-107.

Barret-Connor, E. (1995). The economic and human costs of osteoporosis fracture. The American Journal of Medicine, 98, 2A-3S-2A-11S.

Bassey,E.J., Rothwell, M.C., Littlewood, J.J., & Pye, D.W. (1998). Pre-and postmenopausal     women have different BMD responses to the same high impact exercise. Journal of Bone        & Mineral Research, 13 (12), 1805-1813.

Etherington,J., Harris, P.A., Nandra, D., Hart, D. J., Wolman, R.L., Doyle, D.V., & Spector,     R.D. (1996). The effect of weight-bearing exercise on bone mineral density: A study of           female ex-elite athletes and the general population. The Journal of Bone and Mineral    Research, 11, 1333-1338.

Kriska, A., Sandler, R., Cauley, J., LaPorte, R., Hom, D., & Pambianco, G. (1988). The assessment of historical physical activity and its relation to adult bone parameters.          American Journal of Epidemiology, 127, 1053-1063.

NIH Consensus, P. (2001). Osteoporosis prevention, diagnosis, and therapy. JAMA, 285(6), 785-          795.

Kramer, S. H and Osis, L. D. (1982). Factors Contributing to calcium loss in aging. The American Journal of Clinical Nutrition. 36 (October);776-787.

Wahner, H.W., Dunn, W.L., Riggs, B.L.(1984). Assesstment of Bone Mineral. Part 1. J. Nucl. Med. 25: 1134.

Wellness & prevention sourcebook: New approaches to achieving healthier population. (1998). New York, NY: Faulkner & Gray

Wolff, I., vonCroonenburg, J.J., Kemper, H.C., Kostene, P.J. & Twisk, J.W. (1999). The effect             of exercise training programs on bone mass: A meta-analysis of published control trial in     pre- and postmenopausal women. Osteoporosis International, 9 (1), 1-12.

 

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