1 / 53

Chapter 11

Chapter 11. Physical Activity and Osteoporosis. Physical Activity and Osteoporosis. Osteoporosis

novia
Download Presentation

Chapter 11

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 11 Physical Activity and Osteoporosis

  2. Physical Activity and Osteoporosis Osteoporosis • is a disease of bone - leading to an increased risk of fracture. In osteoporosis the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered. Source = http://en.wikipedia.org Physical Activity and Osteoporosis

  3. Physical Activity and Osteoporosis • Osteoporosis is defined by the World Health Organization (WHO) in women as a bone mineral density 2.5 standard deviations below peak bone mass (See Table 11.1, next slide) as measured by DXA; the term "established osteoporosis" includes the presence of a fragility fracture. • Bone mineral density between 1 and 2.5 standard deviations below that of young adults aged 20 to 29 years indicates osteopenia (i.e., low bone mass), which is a direct risk factor for osteoporosis (WHO) Source = http://en.wikipedia.org Physical Activity and Osteoporosis

  4. Physical Activity and Osteoporosis • For each standard deviation decline in bone mass in the hip, the risk of fracture increases threefold. • A woman’s lifetime risk of hip fracture is equal to her combined risk of breast, uterine, and ovarian cancer. Physical Activity and Osteoporosis

  5. Physical Activity and Osteoporosis – Magnitude of the Problem • The annual prevalence of diagnosed osteoporosis in the United States is about 10 million people; 80% are women. • It is estimated that 44 million Americans ages 50 or older, 55% of adults, have either osteoporosis or osteopenia. • Bone mass is generally lowest among women who are white or Asian, thin framed, and sedentary. • The prevalence of osteoporosis is expected to continue to increase in nations that have increasing life expectancies and hence an increasing number of older people. • Figure 11.1 (next slides) illustrates the projected trends for osteoporosis and osteopenia among U.S. women and men. Physical Activity and Osteoporosis

  6. Physical Activity and Osteoporosis – Magnitude of the Problem Figure 11.1 (a) Osteoporosis trends projected from 2002 to 2020 in the United States for adults 50 years and older. Projections based on NHANES III data. Physical Activity and Osteoporosis

  7. Physical Activity and Osteoporosis – Magnitude of the Problem Figure 11.1 (b) Osteopenia trends projected from 2002 to 2020 in the United States for adults 50 years and older. Projections based on NHANES III data. Physical Activity and Osteoporosis

  8. Physical Activity and Osteoporosis – Fractures and Mortality According to estimates, more than 2 million fractures were attributable to osteoporosis or osteopenia in the U.S. in 2005, including the following: • 297,000 hip fractures • 547,000 vertebral fractures • 397,000 wrist fractures • 135,000 pelvic fractures • 675,000 fractures at other sites Annual fracture incidence is expected to be more than 3 million by the year 2025. Osteoporotic fractures are an important cause of disability and mortality in the elderly. About 20% of patients who fracture a hip die in the year following the fracture, and 50% of the survivors become dependent on others for care. Physical Activity and Osteoporosis

  9. Physical Activity and Osteoporosis – Fractures and Mortality • Vertebral fractures, including micro-compression or crush fractures, account for half of all fractures. • One in four people older than 70 years has some compression fractures of the vertebrae that can lead to kyphosis of the thoracic spine (“Dowager’s hump”). • White women lose an average of 6.4 cm (2.5 in.) of height after menopause. • Complications of osteoporosis represent an economic burden to public health. • The direct cost of treating osteoporotic fractures of the proximal femur, radius, and vertebrae was about $19 billion in 2005. • By the year 2025, it is predicted to be $25 billion. Physical Activity and Osteoporosis

  10. Physical Activity and Osteoporosis – Etiology • There are two main categories of osteoporosis. Primary osteoporosis includes age-related (type II, or senile) bone loss and postmenopausal (type I,) bone loss (note error in text) • Type II - Senile Osteoporosis • caused by long term calcium deficiency; • affects patients over age of 75- these patients have already lost most of the bone they ever will lose- they differ little in bone density from peers w/o fractures- equal loss of cortical and trabecular bone;- low bone turnover- in type II osteoporosis, fractures occur most often in vertebrae & femoral neck, followed by fractures of pelvis, humerus, & tibiaSource = Wheeless' Textbook of Orthopaedics Physical Activity and Osteoporosis

  11. Physical Activity and Osteoporosis – Etiology • Type I - Postmenopausal Osteoporosis • - due to loss of estrogen & affects postmenopausal women;- primarily loss of trabecular bone:- associated w/ greater decline in medullary bone & preservation of cortex;- trabecular-bone loss is three times the rate of normal- rate of cortical-bone loss is only slightly above normal;- there is accelerated bone loss, decreased calcium absorption;- defect in calcium absorption may aggravate bone loss;- loss of structural trabeculae weakens vertebrae & predisposes them to acute collapse; vertebral bodies are skeletal elements most at risk- vertebral fractures are usually of the "crush" type associated w/ large deformation and pain;- vertebralandColles fracturesare common Physical Activity and Osteoporosis

  12. Physical Activity and Osteoporosis – Etiology Secondary osteoporosis is caused by another disease but may not be independent of age or menopause. (FYI) • Generalized Secondary Osteoporosis Causes • hypogonadism ● rheumatoid arthritis • thyrotoxicosis ● hyperadrenocorticism • hyperprolactinemia ●anorexia nervosa • pregnancy ● diabetes mellitus • chronic liver disease ●vitamin D deficiency • chronic heparin use ●alcoholism • osteogenesis ●homocystin • anticonvulsants ●myeloma Physical Activity and Osteoporosis

  13. Physical Activity and Osteoporosis – Etiology - Sex Differences • At all ages, men have more bone mass than women, and men’s natural bone loss is more gradual. • Women lose bone at a rate of about 1% to 2% beginning around age 35 • During lactation, there is a slight, transient increase in bone loss to 7% in the first six months after childbirth, which returns to the normal rate of loss at the resumption of menses • Women can lose up to 20% of their bone mass in the five to seven years after menopause. • The larger and faster decreases in bone mass in women explain most of the difference in prevalence of osteoporotic fractures between women and men. • It is believed that the marked decline in levels of estrogen after menopause accounts for the greater bone loss experienced by women; 75% or more of the bone loss that occurs in women during the first 15 years after menopause is attributable to estrogen deficiency. Physical Activity and Osteoporosis

  14. Physical Activity and Osteoporosis – Bone renewal and loss (involution) • To understand how bone involution might be retarded by physical activity, it is necessary to understand the basics of bone renewal. • The endosteum is the layer of cells lining the inner surface of bone in the central medullary cavity. • The exosteum refers to bone cells that are outside the central medullary cavity. • After about age 30 to 40, endosteal bone is lost at a faster rate than exosteal bone is deposited. This is called bone involution, which results in osteopenia and is a risk factor for osteoporosis. • There are two types of bone: cortical bone and trabecular bone. Cortical, or compact, bone is found mainly in the shaft of long bones and accounts for about 80% of all bone. Trabecular bone is spongy tissue, has a lattice or honeycomb design, and is found in the vertebrae, pelvis, flat bones, and ends of the long bones. Physical Activity and Osteoporosis

  15. Physical Activity and Osteoporosis – Bone renewal and loss (involution) • Trabecular bone has more surface area per volume and is more metabolically active (e.g., a higher flux of minerals occurs between bone and blood) than cortical bone • The formation and resorption of trabecular bone occur about six times faster than in cortical bone. Thus, trabecular bone is more susceptible to osteoporotic disease White women lose an average of 50% of trabecular bone and 30% of cortical bone over their lifetimes (mainly after menopause), while men lose about 15% of trabecular and 12% of cortical bone mass. Physical Activity and Osteoporosis

  16. Physical Activity and Osteoporosis – Bone renewal and loss (involution) Bone remodeling is a continuous process involving hormonal and local regulation of three types of cells: osteoclasts, osteoblasts, and osteocytes. Osteoclasts are phagocytes that digest old bone cells and thus are involved in bone resorption (i.e., breakdown).. Osteoblasts rebuild by forming new bone cells (i.e., osteocytes) from collagen to make an osteoid matrix. The osteoid matrix provides the infrastructure for the mineralization of bone (e.g., by calcium and phosphorus) and, along with trabecular bone, gives bone its mechanical, elastic, and tensile strength. Physical Activity and Osteoporosis

  17. Physical Activity and Osteoporosis – Bone renewal and loss (involution) • Increases (during growth) and decreases (with age) in BMD depend on the balance of activity of osteoclasts and osteoblasts. • After peak bone mass is attained, the activity of osteoclasts gradually outpaces that of osteoblasts, leading to an accumulation of cavities in the bone’s osteoid matrix • During normal aging (i.e., without lifestyle intervention), women lose both endosteal and periosteal bone. • In contrast, aging men have less net bone loss because their periosteal bone remains more stable, which can partly compensate for their endosteal bone loss to help retard loss of bone strength. Physical Activity and Osteoporosis

  18. Physical Activity and Osteoporosis – Hormonal Influences • Parathyroid hormone contributes to bone remodeling by stimulating resorption of calcium from the bone, while calcitonin inhibits resorption. • It is not yet fully understood how reproductive hormones such as estrogen and testosterone help protect against bone loss. • Low levels of vitamin D is a risk factor for osteoporosis • Vitamin D is converted in the kidney to the biologically active metabolite of vitamin D, which enhances the absorption of dietary calcium by bone. • The presence of receptors for estrogen on osteoblasts indicates that estrogen can have a direct effect on osteogenesis. Estrogen stimulates several bone growth factors, and inhibits factors that promote osteopenia • Estrogen also stimulates the synthesis of calcitonin, which inhibits bone resorption and increases vitamin D receptors in osteoblasts Physical Activity and Osteoporosis

  19. Physical Activity and Osteoporosis – Risk Factors and Prevention • Risk factors for osteoporotic fracture can be split between non-modifiable and (potentially) modifiable. • In addition, there are specific diseases and disorders in which osteoporosis is a recognized complication. • Medication use is theoretically modifiable, although in many cases the use of medication that increases osteoporosis risk is unavoidable. Source = http://en.wikipedia.org Physical Activity and Osteoporosis

  20. Physical Activity and Osteoporosis – Risk Factors and Prevention Risk Factors for Osteoporosis • Modifiable • Cigarette smoking • Excessive alcohol intake • Low testosterone levels • Vitamin D intake • physical inactivity • Calcium intake • Anorexia or bulimia • Amenorrhea • Medications (e.g., benzodiazepenes) • Unmodifiable • Heredity • Small body frame • Female sex • Race (European or Asian) • Age • Postmenopause • Amenorrhea • Premature menopause Physical Activity and Osteoporosis

  21. Physical Activity and Osteoporosis – Risk Factors and Prevention • Dietary Calcium and Vitamin D • A diet containing an adequate amount of calcium, vitamin D, and protein is recommended to promote bone health and reduce the risks of osteopenia and osteoporosis. • Inadequate calcium is a risk factor for osteopenia and osteoporosis. • The recommended calcium intake during adolescence and adulthood, depending on age, is between 1000 and 1300 mg per day. • Vitamin D is necessary for the body to absorb calcium from food. • Its synthesis depends on sun exposure. Though sufficient amounts of vitamin D can be synthesized in the skin with 10 to 15 min of direct exposure of the face and extremities to sunlight two or three days each week • The biosynthesis of vitamin D is less in dark-skinned people and lessens as people age. Physical Activity and Osteoporosis

  22. Physical Activity and Osteoporosis – Risk Factors and Prevention • Hormone Replacement Therapy (HRT) • The World Health Organization concluded more than a decade ago that women who take estrogen for at least seven years between the onset of menopause and the age of 75 have a 50% reduction in risk of fractures as well as CHD (WHO Study Group 1994). However, some studies have shown increased risk of breast cancer and CVD after estrogen or estrogen plus progestin replacement therapy. • Hormone replacement therapy can protect bone from rapid demineralization, typical of the early postmenopausal period, and thus decrease fracture rates in postmenopausal women. Physical Activity and Osteoporosis

  23. Physical Activity and OsteoporosisMeasurement Techniques • Dual energy X-ray absorptiometry (DXA), previously DEXA) is a means of measuring bone mineral density (BMD). Two X-ray beams with differing energy levels are aimed at the patient's bones. When soft tissue absorption is subtracted out, the BMD can be determined from the absorption of each beam by bone. DXA is the most widely used and most thoroughly studied bone density measurement technology. A T-score of -2.5 or less is indicative of osteoporosis. Source = http://en.wikipedia.org Physical Activity and Osteoporosis

  24. Physical Activity and Osteoporosis – The Evidence • There is scientific consensus that physical inactivity is associated with decreased bone mass. • Physical activity involving high-intensity loading of bone promotes bone density and may help prevent osteoporosis • A greater amount of physical activity (i.e., frequency, duration, or intensity or more than one of these) has an inverse dose–response relation with the risk of fractures of the hip • Although estrogen-deficient women can benefit from weight-bearing exercise, exercise alone cannot substitute for HRT during the early postmenopausal phase of rapid bone loss. Physical Activity and Osteoporosis

  25. Physical Activity and Osteoporosis – The Evidence • Cross-Sectional Studies Overview • Weight bearing exercises with higher forces loads offer the greatest protection. Thus, mechanical loading provides protection of bone mass • Greater muscle strength is positively associated with BMD, and increased BMD possibly results from stimulation of bone remodeling by the transfer of the force from the muscle to the bone Physical Activity and Osteoporosis

  26. Physical Activity and Osteoporosis – The Evidence – Prospective Cohort Studies • Nebraska Women • College-aged women • 3.5 yr study • Average gain in BMD in the lumbar spine was 6.8% and was related to both exercise and calcium intake, independently. • Least active women gained an average of 0.3% whereas the most active gained 8.4%. Physical Activity and Osteoporosis

  27. Physical Activity and Osteoporosis – The Evidence – Prospective Cohort Studies • Rancho Bernardo, California, Men • The BMD of 507 ambulatory community-dwelling men 45 to 92 years old was assessed at the hip by DXA between 1988 and 1992 and again four years later • The main predictors of BMD loss were an age of 75 years or older, baseline BMI <24 kg/m2, four-year weight loss of 5% or more, current smoking, and physical inactivity. • A high proportion of the men reported regular exercise (30.6% exercised often, and 48.9% exercised sometimes) three or more times per week Physical Activity and Osteoporosis

  28. Physical Activity and Osteoporosis – The Evidence – Prospective Cohort Studies • Nord-TrøndelagHealth Study (HUNT) • The Nord-Trøndelag Health Study (HUNT) is an ongoing population-based study in North Trøndelag, one of Norway’s 19 counties. • More than 20,000 women completed an initial health survey during 1984-1986 (HUNT 1), and a follow-up survey was conducted during 1995 through 1997 (HUNT 2). • Premenopausal women who said they participated in high-intensity leisure-time physical activity and also did heavy physical occupational work in both 1984 and 1995 had about a 55% reduction in odds of low BMD Physical Activity and Osteoporosis

  29. Physical Activity and Osteoporosis – The Evidence Prospective Cohort Studies • Finnish Youths • Males and Females aged 9-18 yrs • 11 yr study • BMD higher (8% women; 10% men) in the most physically active compared to most inactive • Exercise predicted BMD in the femoral neck and lumbar spine of the men, independent of smoking Physical Activity and Osteoporosis

  30. Physical Activity and Osteoporosis – The Evidence Prospective Cohort Studies • The University of Saskatchewan Bone Mineral Study • Males and Females aged 8-14 yrs • 6 yr study • BMC (bone mineral concentration) higher in the femoral neck and lumbar spine, and total body in both males and females who were physically active compared to the inactive Physical Activity and Osteoporosis

  31. Physical Activity and Osteoporosis – The Evidence Prospective Cohort Studies • Amsterdam Growth and Health Longitudinal Study • Males and Females aged 13-29 yrs • Bone Mass (lumbar spine, femoral neck) was positively associated with physical activity Physical Activity and Osteoporosis

  32. Physical Activity and Osteoporosis – The Evidence Prospective Cohort Studies • Penn State Young Women’s Health Study • Females aged 12-18 yrs • Cumulative amount of sports participation activity and exercise activity was moderately related to (r = 0.42) to femoral BMD Physical Activity and Osteoporosis

  33. Physical Activity and Osteoporosis – The Evidence Prospective Cohort Studies • Swedish Youth • Males / Females aged 12-16 yrs • BMD were 8-9% higher in boys who increased the frequency of physical education compared to those boys who did not. Physical Activity and Osteoporosis

  34. Physical Activity and Osteoporosis – The Evidence Clinical Studies: Endurance Exercise Training • Summary • 13 Studies reviewed in Meta-Analysis • Exercise training led to the prevention or reversal of about 1% of the annual loss of BMD in the lumbar spine and femoral neck • See Table 10.4, p221, text for summary of studies. These studies range from 8 mo – 2 yr, examined both men and women, aged 8-68 yrs, and showed BMD gains ranging from 1-10% Physical Activity and Osteoporosis

  35. Physical Activity and Osteoporosis – The Evidence Clinical Studies: Endurance Exercise Training • Summary • Though most studies averaged 1% increase in BMD of the lumbar spine with 1% decrease in controls, endurance studies in post-menopausal women have mixed results. • Overall, it does appear that vigorous, high intensity, repetitive, weight bearing aerobic training can result in small net increases in bone mass per year in women. Physical Activity and Osteoporosis

  36. Physical Activity and Osteoporosis – The Evidence Clinical Studies: Resistance Exercise Training • Summary • High-intensity progressive resistance training increased BMD at the lumbar spine 1%, but not at the femoral neck. • In men, increases of about 2.6%(2.1% in the exercisers vs. −0.5% in the controls) were found at the femur and lumbar spine. These effects were statistically significant only for men older than 31 Physical Activity and Osteoporosis

  37. Physical Activity and Osteoporosis – The Evidence Clinical Studies: Resistance Exercise Training • Postmenopausal Women • Several studies show that resistance training can increase bone mass at specific sites, independent of estrogen replacement (site specific where force is loaded) • Bone mass did not increase on non-stressed areas, it actually decreased Physical Activity and Osteoporosis

  38. Physical Activity and Osteoporosis – The Evidence Clinical Studies: Resistance Exercise Training • Site Specific Loading • Increases in BMD seen on bone sites that are force loaded with resistance activities, but not in areas that are not loaded • Eccentric Work may be more effective in bone formation than concentric work because eccentric work generates more force production per unit area than concentric work Physical Activity and Osteoporosis

  39. Physical Activity and Osteoporosis – The Evidence Clinical Studies: Exercise Plus Hormone Replacement Therapy in Postmenopausal Women • Exercise alone cannot substitute for hormone replacement therapy (HRT) during early postmenopausal phase of rapid bone loss • During the first five years after menopause, women who do not take estrogen can lose up to 35% of their bone mass. • The combination of HRT and exercise may yield the greatest effect on bone loss because estrogen may enhance the osteogenic effect of mechanical loading Physical Activity and Osteoporosis

  40. Physical Activity and Osteoporosis – Strength of the Evidence Summary • The cumulative, average effect in randomized trials of resistance training on BMD in the lumbar spine and the femoral neck in both pre- and postmenopausal women was about a 0.9% (approx. 1%) per year when compared with women who did not exercise • Few observational retrospective and prospective cohort studies and case–control studies have suggested that physical activity reduces the risk of falls and osteoporotic fractures (This section of the chapter is FYI, only) There are few well-controlled epidemiologic studies linking physical activity with risk of developing osteoporosis or fractures in a large population base. Physical Activity and Osteoporosis

  41. Physical Activity and Osteoporosis – Strength of the Evidence Summary • Studies collectively suggest that resistance exercise is associated with: • (1) an increase in peak bone mass and, • (2) a slowing of osteopenia during middle age. • A few studies also suggest that resistance exercise training has potential to promote: • (1) a reversal of bone mass loss in old age, • (2) a reduction in risk factors for falls and the incidence of falls, and, • (3) a reduction in fractures resulting from falls among the elderly Physical Activity and Osteoporosis

  42. Physical Activity and Osteoporosis – Strength of the Evidence Summary – Modification and Confounders • The high intensity exercise / weight training may be contraindicated in the elderly, and lower strain or inability to complete the training regimen can confound results • Poor control of other factors that can improve bone density (Vitamin D , Calcium, HRT) may confound the results of exercise training studies • Bone mass differences at baseline can also explain various treatment effects. Individuals with low bone mass at the beginning of a training program are likely to show a greater increase in bone mass than those who start out with higher bone mass. • Weight loss as a result of the training study might lead to underestimation of the effect of the program Physical Activity and Osteoporosis

  43. Physical Activity and Osteoporosis – Strength of the Evidence • Temporal Sequence • Prospective studies have been conducted for periods of time that range from 3 mo. - 12 yrs. • Strength of the Association • Prospective cohort studies show a 3-10% increase in BMD and an average reduction in the risk of hip fractures of the hip ranging from 20-40% among physically active persons • The overall effect of randomized control trials on middle-aged women is the reduction or reversal of bone loss with age of about 1% per year. • Even a 1% to 2% change in BMD, coupled with increased strength and better balance, might lower fracture risk as much as 50% Physical Activity and Osteoporosis

  44. Physical Activity and Osteoporosis – Strength of the Evidence • Consistency • Most studies have focused on the populations at greatest risk, however, the overall evidence is that the osteogenic effect of exercise is similar for both sexes and all races. • In adults, the limited data from intervention trials suggest that any increase in bone strength is due largely to increased bone mineral, reduced endocortical bone loss, or both, rather than an increase in bone size. Physical Activity and Osteoporosis

  45. Physical Activity and Osteoporosis – Strength of the Evidence • Dose Response • There is no direct evidence to indicate whether the effect of physical activity on maintaining bone mass in premenopausal women and retarding or reversing bone loss in postmenopausal women is dose dependent • Site-specific effects on BMD are greater for resistance exercise and sport activities that place a high force load on bone tissue Physical Activity and Osteoporosis

  46. Physical Activity and Osteoporosis – Strength of the Evidence • Dose Response • Minimum levels of physical activity associated with reduced fracture risk in adults are at least 9 to 14.9 MET hours per week of physical activity, more than four hours per week of walking, at least 1290 kcal per week of physical activity, and more than one hour per week of physical activity Physical Activity and Osteoporosis

  47. Physical Activity and Osteoporosis – Strength of the Evidence • Biological Plausibility • The magnitude of loading stress on bone has a greater influence on bone density than the number of cycles of bone loading (force more important than frequency) • Mechanical loading causes a change to the bones microstructure architecture (Wolff’s Law), especially in cortical bone (see next slides) Physical Activity and Osteoporosis

  48. Physical Activity and Osteoporosis – Strength of the Evidence Figure 11.7 Mechanical loads that bend bone will increase periosteal cortical bone. Physical Activity and Osteoporosis

  49. Physical Activity and Osteoporosis – Strength of the Evidence Figure 11.8 Changes in cortical bone in female tennis players. Magnetic resonance imaging of cortical bone (outer layer) and medullary bone (inner layer) of the non-dominant and dominant arms of postpubertal tennis players. Bone mineral content strength was about 10% to 15% greater in the playing arm because of increases in periosteal bone that occurred during prepubertal years of playing and remained stable during continued playing after puberty. Physical Activity and Osteoporosis

  50. Physical Activity and Osteoporosis – Strength of the Evidence • Biological Plausibility • Piezoelectric Effects – stains on the bone mass cause it to bend or vibrate. This causes potential electrical differences across the bones mass (this draws in Ca++ ions to the points of stress to build bone mass) • Prostaglandins formation increases and stimulates new bone synthesis Physical Activity and Osteoporosis

More Related