• unlimited access with print and download
    $ 37 00
  • read full document, no print or download, expires after 72 hours
    $ 4 99
More info
Unlimited access including download and printing, plus availability for reading and annotating in your in your Udini library.
  • Access to this article in your Udini library for 72 hours from purchase.
  • The article will not be available for download or print.
  • Upgrade to the full version of this document at a reduced price.
  • Your trial access payment is credited when purchasing the full version.
Buy
Continue searching

The relationship between body composition and bone mineral density in women

ProQuest Dissertations and Theses, 2009
Dissertation
Author: Pei-Yang Liu
Abstract:
Purpose. The purpose of this study was to investigate the relationships between body composition (fat and lean mass), body weight, body mass index (BMI) and bone mineral density (BMD) and bone mineral content (BMC) in women across the age span. Methods. 1046 healthy Caucasian women (49.9 ± 15.9 years old) were recruited and categorized to four age groups, ranging from 18 to 35 years old, 35 years to before the age of menopause, menopause to 65 years and over 65 years old. Each different age group was further categorized according to subjects' body mass index (BMI < 25, BMI = 25-29.9, and BMI ≥ 30). Measurements included anthropometrics, body composition and BMC/BMD by dual-energy x-ray absorptiometry (DXA). Results. Subjects in the younger groups were taller, weight less and had greater total body BMC/BMD and BMD at spine, femoral neck, and total femur (p <0.05) compared with older subjects. Obese women had higher total lean and fat mass, and the highest BMD/BMC in all skeletal sites (p <0.05) among different age groups. Weight, BMI, total lean, and total fat mass were positively correlated with total body BMC/BMD, BMD of all skeletal sites among different age groups. The results from multiple linear regression models revealed that weight was a significant predictor of total body BMC/BMD, BMD of all skeletal sites in women of different age groups, gonadal status, and different BMI, except overweight women. Both lean and fat mass were important determinants of total body BMC/BMD, BMD at femur and forearm in premenopausal women though total lean mass had greater effect than total fat mass. Total fat mass was the only significant predictor of total body BMC/BMD, BMD at other sites in postmenopausal women. Furthermore, total fat mass became more important with the increased body weight. Further analysis of covariance in subjects stratified by body weight and percent body fat revealed that high percent body fat seemed to have negative effect on bone mass in total body BMC/BMD and BMD at spine, femoral neck and forearm when mechanical loading effect of body weight was controlled. Conclusions. These results show that overweight/obese women had higher BMD in all skeletal sites than normal-weight women. Lean mass was an important predictor of BMD in premenopausal women and fat mass became more important in postmenopausal women. Higher fat mass however, may not have beneficial effect on bone mass when mechanical loading of weight is accounted for.

TABLE OF CONTENTS

LIST OF TABLES ......................................................................................................................... vi

LIST OF FIGURES ..................................................................................................................... viii

ABSTRACT ................................................................................................................................... ix

CHAPTER 1 ................................................................................................................................... 1

INTRODUCTION .......................................................................................................................... 1

CHAPTER 2 ................................................................................................................................... 6

REVIEW OF LITERATURE ......................................................................................................... 6

CHAPTER 3 ................................................................................................................................. 23

RESEARCH DESIGN AND METHODS .................................................................................... 23

CHAPTER 4 ................................................................................................................................. 27

RESULTS ..................................................................................................................................... 27

CHAPTER 5 ................................................................................................................................. 61

DISCUSSION ............................................................................................................................... 61

APPENDIX A ............................................................................................................................... 74

APPENDIX B ............................................................................................................................... 75

APPENDIX C ............................................................................................................................... 78

APPENDIX D ............................................................................................................................... 80

REFERENCES ............................................................................................................................. 81

BIOGRAPHICAL SKETCH ........................................................................................................ 94

vi

LIST OF TABLES

Table 1. Characteristics of the study population ........................................................................... 27

Table 2. Comparison of anthropometrics and bone mineral density across the age groups ......... 31

Table 3. Comparison of anthropometrics and bone mineral density in all women across the body mass index (BMI) categories ........................................................................................................ 32

Table 4. Comparison of anthropometrics and bone mineral density in women aged 18 to 35 years across the body mass index (BMI) categories .............................................................................. 33

Table 5. Comparison of anthropometrics and bone mineral density in women over 35 years to before the age of menopause across the body mass index (BMI) categories ............................... 34

Table 6. Comparison of anthropometrics and bone mineral density in women from menopause to 65 years across the body mass index (BMI) categories ................................................................ 35

Table 7. Comparison of anthropometrics and bone mineral density in women over 65 years across the body mass index (BMI) categories .............................................................................. 36

Table 8. Pearson’s correlation coefficient between bone mineral density and anthropometrics in all women (n=1046) ...................................................................................................................... 46

Table 9. Pearson’s correlation coefficient between bone mineral density and anthropometrics in women aged 18 to 35 years ........................................................................................................... 46

Table 10. Pearson’s correlation coefficient between bone mineral density and anthropometrics in women over 35 years to before the age of menopause ................................................................. 47

Table 11. Pearson’s correlation coefficient between bone mineral density and anthropometrics in postmenopausal women up to 65 years ........................................................................................ 48

Table 12. Pearson’s correlation coefficient between bone mineral density and anthropometrics in women over 65 years .................................................................................................................... 49

Table 13. Multiple linear regression between BMD/BMC of various skeletal sites as dependent variables and weight, height and age as independent variables in all women and in those stratified by gonadal status............................................................................................................ 50

Table 14. Multiple linear regression between BMD/BMC of various skeletal sites as dependent variables and weight, height and age as independent variables in women stratified by BMI ...... 51

Table 15. Multiple linear regression between BMD/BMC of various skeletal sites as dependent variables and weight, height and age as independent variables in women across the age groups 52

vii

Table 16. Multiple linear regression between BMD/BMC of various skeletal sites as dependent variables and anthropometrics as independent variables in all women and in those stratified by gonadal status ................................................................................................................................ 53

Table 17. Multiple linear regression between BMD/BMC of various skeletal sites as dependent variables and anthropometrics as independent variables in women stratified by BMI ................ 55

Table 18. Multiple linear regression between BMD/BMC of various skeletal sites as dependent variables and anthropometrics as independent variables in women across the age groups .......... 57

viii

LIST OF FIGURES

Figure 1: Diagram of sample stratification and sample size in each group categorized by age and BMI ............................................................................................................................................... 28

Figure 2. Scatterplots with regression lines showing relationship between age and lean body mass (A), fat mass (B), total body BMC (C), total body BMD (D), spine L2-L4 BMD (E), Radius 33% BMD (F), femoral neck BMD (G), total femur BMD (H). ...................................... 30

Figure 3. Comparison of the body mass index (BMI) across the age groups ............................... 37

Figure 4. Comparison of total body BMD across the age groups ................................................. 38

Figure 5. Comparison of total body BMC across the age groups ................................................. 39

Figure 6. Comparison of spine BMD across the age groups ........................................................ 40

Figure 7. Comparison of femoral neck BMD across the age groups ............................................ 41

Figure 8. Comparison of total femur BMD across the age groups ............................................... 42

Figure 9. Comparison of forearm BMD across the age groups .................................................... 43

Figure 10. Comparison of total body lean mass across the age groups ........................................ 44

Figure 11. Comparison of total body fat mass across the age groups........................................... 45

Figure 12. Total body BMC/BMD (A, B) and BMD of spine (C), femoral neck (D), and forearm (E) in subjects by percentage fat mass in normal-weight, overweight and obese women ............ 60

ix

ABSTRACT

The relationship between body composition and bone mineral density in women Purpose: The purpose of this study was to investigate the relationships between body composition (fat and lean mass), body weight, body mass index (BMI) and bone mineral density (BMD) and bone mineral content (BMC) in women across the age span. Methods: 1046 healthy Caucasian women (49.9 ± 15.9 years old) were recruited and categorized to four age groups, ranging from 18 to 35 years old, 35 years to before the age of menopause, menopause to 65 years and over 65 years old. Each different age group was further categorized according to subjects’ body mass index (BMI < 25, BMI = 25-29.9, and BMI ≥ 30). Measurements included anthropometrics, body composition and BMC/BMD by dual-energy x-ray absorptiometry (DXA). Results: Subjects in the younger groups were taller, weight less and had greater total body BMC/BMD and BMD at spine, femoral neck, and total femur (p<0.05) compared with older subjects. Obese women had higher total lean and fat mass, and the highest BMD/BMC in all skeletal sites (p<0.05) among different age groups. Weight, BMI, total lean, and total fat mass were positively correlated with total body BMC/BMD, BMD of all skeletal sites among different age groups. The results from multiple linear regression models revealed that weight was a significant predictor of total body BMC/BMD, BMD of all skeletal sites in women of different age groups, gonadal status, and different BMI, except overweight women. Both lean and fat mass were important determinants of total body BMC/BMD, BMD at femur and forearm in premenopausal women though total lean mass had greater effect than total fat mass. Total fat mass was the only significant predictor of total body BMC/BMD, BMD at other sites in postmenopausal women. Furthermore, total fat mass became more important with the increased body weight. Further analysis of covariance in subjects stratified by body weight and percent body fat revealed that high percent body fat seemed to have negative effect on bone mass in total body BMC/BMD and BMD at spine, femoral neck and forearm when mechanical loading effect of body weight was controlled. Conclusions: These results show that overweight/obese women had higher BMD in all skeletal sites than normal-weight women. Lean mass was an important predictor of BMD in premenopausal women and fat mass became more important in postmenopausal women. Higher fat mass however, may not have beneficial effect on bone mass when mechanical loading of weight is accounted for.

1

CHAPTER 1

INTRODUCTION An important public health challenge worldwide is osteoporosis a disorder characterized by low bone mass and microarchitectural deterioration of bone tissue. It increases skeletal fragility, fracture susceptibility and is a significant risk factor for morbidity and mortality among the elderly (Melton, 2003). In the United States, osteoporosis affects at least 25 million Americans with the highest prevalence in postmenopausal women (National Osteoporosis Foundation, 1998). The prevalence of osteoporosis is expected to increase as the population ages (National Osteoporosis Foundation, 1998). The National Osteoporosis Foundation estimates that costs associated with this disorder will be on the order of $19 billion in 2005, with $7 billion per year related to hip fractures alone ( National Osteoporosis Foundation, 2009). Caucasian women older than 50 have a 40% chance of sustaining an osteoporosis-related fracture during the remainder of their lifetime. Hip fractures are of particular concern because of increased risk of mortality within 1 year of the occurrence (Kirk, Spangler, & Celestino, 2000). Researcher tried to find out the relationship between overweight and osteoporosis. Obesity, defined as excess body fat accumulated in the body, is another important clinical and public health challenge worldwide. It has been estimated that 1.1 billion adults and 10% children are overweight or obese (Haslam & James, 2005). Between 2003-2004 the National Health and Nutrition Examination Survey (NHNES) indicated that approximately 66.3% adults aged 20 years or older in the US were either overweight or obese and that 32.2% adults were obese (Ogden et al., 2006). Obesity significantly increases the rate of diseases, such as type 2 diabetes, cardiovascular disease, stroke, some types of cancer, and causes premature death worldwide (Calle & Kaaks, 2004; Calle, Rodriguez, Walker-Thurmond, & Thun, 2003; Chan, Rimm, Colditz, Stampfer, & Willett, 1994; Hu et al., 2004; Krauss, Winston, Fletcher, & Grundy, 1998; Kurth et al., 2002; Lee, Manson, Hennekens, & Paffenbarger, 1993; Rexrode et al., 1997). The prevalence of overweight or obesity among women aged 20-74 continuously increased from 1980 to 2000 in the NHANES. The prevalence of overweight females rose from

2

41-62% and obesity rose from 41-62% from 2000 through 2004 (Ogden et al., 2006). Women are more at risk for being overweight or obese, especially as they age. Therefore, as obesity keeps increasing among U.S. women, the prevention and treatment of overweight and obesity are crucial to ensure a healthier life for women especially after menopause. Body mass index (BMI) is a common method used to assess weight status and determines the degree of overweight/obesity. It is calculated by dividing the weight (kg) by the square of the height (m 2 ) (National Institute of Health, 1998). The World Health Organization (WHO) recommends using BMI to classify weight status in adults 20 years and older: 18.5–24.9 kg/m 2 (is considered normal-weight), 25.0–29.9 kg/m 2 (overweight), 30.0–39.9 kg/m 2 (obese), and ≥ 40 kg/m 2 (extremely obese). Although calculating one’s BMI is the easiest method to determine one’s weight status, it has limitations, including the fact that it cannot distinguish between fat and lean mass. As a result, athletes and muscular people might be classified as overweight based on BMI assessment. Therefore, other methods (e.g., dual energy x-ray absorptiometry; DXA) may be more appropriate for some populations. DXA, when available, is the preferred method of assessment since it provides more accurate and objective measurement of percent body fat and overweight/obesity status. For many years, overweight/obesity and osteoporosis were thought to be mutually exclusive. More recently, it has been demonstrated that bone mass is positively associated with body weight (Cifuentes et al., 2003; Dawson-Hughes, Shipp, Sadowski, & Dallal, 1987). This positive relationship may not necessarily represent a correlation between obesity and bone mass but obesity is characterized as excessive adipose tissue rather than higher lean mass. The question remains whether or not fat mass and/or fat free mass, influence bone mass. Many researchers have focused on the relationship between body composition and bone mineral density (BMD)/bone mineral content (BMC) among young and postmenopausal women (Ilich-Ernst, Brownbill, Ludemann, & Fu, 2002). However, less is known about this relationship in middle-aged women. Current studies have focused on how body weight affects BMD but few studies have investigated the influence of a range of body weights (i.e., normal-weight, overweight, and obesity)

3

and body composition (lean and fat masses) on BMD and BMC in women of different ages. Therefore, to address the gap in the scientific understanding of body weight and BMD, the overall purpose of this study was to investigate the relationships between body composition (i.e., fat and lean mass), total weight, BMI and bone mineral density and bone mineral content in women across the age span. Specific Aims Specific Aim 1. To determine the association between weight/BMI and bone mineral density/content in women of different ages. The influence of BMI or total body weight on bone mass has been documented (Cifuentes et al., 2003; Dawson-Hughes et al., 1987). Total body weight is positively associated with whole body (Reid, Plank, & Evans, 1992), spine (Reid, Ames et al., 1992), and femoral neck BMD (Siris et al., 2001) in premenopausal women. The association between body weight, BMC and BMD was also found in overweight perimenopausal -- defined as beginning its transition into menopause, (Brot, Jensen, & Sorensen, 1997; Pesonen et al., 2005) and overweight postmenopausal women (Chen, Lohman, Stini, Ritenbaugh, & Aickin, 1997; Kirchengast, Peterson, Hauser, & Knogler, 2001). Few studies investigated the correlation between BMC/BMD and body weight in obese postmenopausal women. This aim tested the working hypothesis that there is a positive relationship between weight/BMI and BMD/BMC in all measurable skeletal sites, namely, the total body, spine, hip and forearm. Specific Aim 2. To determine the relationship between fat and lean mass and BMD/BMC in women of different ages. Body composition, including lean and fat tissue, is one of the important predictors of BMD/BMC although it is not clear which one (lean or fat) has greater influence. Some researchers have proposed that total lean mass is a stronger predictor of BMD than fat mass (Chen et al., 1997; Li, Wagner, Holm, Lehotsky, & Zinaman, 2004), whereas others have proposed that total fat mass is stronger associated with BMD (Coin et al., 2000; Reid, Ames et al., 1992; Reid, Plank et al., 1992). Others have shown that both fat

4

and lean mass are equally associated with BMD (Khosla, Atkinson, Riggs, & Melton, 1996; Lim et al., 2004). This aim tested the working hypothesis that lean and fat mass are both positively associated with BMD/BMC in all measurable skeletal sites, namely the total body, spine, hip, and forearm, but the lean mass has a stronger positive relationship. Specific Aim 3. To determine whether higher fat mass negatively affects BMD/BMC in women of different BMI ranges. Obesity is characterized by an excessive fat mass contributing to total body weight. Fat mass increases with age, especially after menopause. It is still unknown whether the effect of weight on BMC and BMD will still remain when fat mass reaches a certain percentage of the weight. Some evidence suggests that obesity may increase the risk of osteoporosis as well (Hsu et al., 2006). This aim tested the working hypothesis that there is no negative effect of fat mass on BMD/BMC in normal-weight women while there is negative effect of fat mass on BMD/BMC in overweight and obese women. Definitions Menopause: the permanent cessation of reproductive fertility occurring some time before the end of the natural lifespan. Bone mineral content (BMC): the amount

of mineral measured in a defined section of bone, expressed as gram. Bone mineral density (BMD): a measure of the amount of bone mineral behind the shadow cast by the bony structure, divided by the area of that shadow and is expressed as bone mineral per unit area (BMC/area). Fat mass: the amount of fat in the body. Lean mass: the weight of the body, less the weight of its fat Assumptions The following assumptions are included: 1. All subjects truthfully reported their age, menopause status, health conditions and supplements intake. 2. All laboratory equipment (scale, stadiometer, DXA) and measurement techniques yielded accurate measurements throughout the entire study period.

5

Delimitations The following delimitations are applied to this study: 1. The subjects were limited to Caucasian women 18-88 years of age that were recruited from Tallahassee, Florida; Storrs, Connecticut; and the surrounding communities in these locales, as well as several municipalities in Croatia. 2. Subjects were excluded for any of the following conditions: pregnancy, uncontrolled hypertension, heart disease, diabetes, thyroid disease, cancer, liver and kidney disease, if taking hormone replacement therapy or medications that affect bone metabolism, and calcium and vitamin D supplementation. 3. If subjects were willing to stop hormone replacement therapy, calcium or vitamin D supplementation for 3 months, they were recruited after that period. 4. Subjects’ weight could not be over the limitation of Lunar iDXA (181.6 kg) and the whole body had to fit within the scanning area. Significance The significance of this study is that it provides information about the relationship between body weight, body composition and BMD/BMC in women across different ages and BMI, as opposed to merely in premenopausal or overweight postmenopausal women. Large numbers of data from participants were utilized that enables the assessment of epidemiological proportions. Different populations of Caucasian women were collected which makes the data applicable for general population. In addition, it elucidated the effect of higher body fat on bone mass. Body weight is composed of bone, lean and fat mass. Many studies have suggested that lean mass may be beneficial to BMD in young adults, and the fat mass is important for maintaining BMD in postmenopausal women. However, conflicting results show that lean mass is important for postmenopausal women and fat mass is the major contributor to bone mass in premenopausal women. These conflicting results require further investigation, which this proposed study explored: Whether higher weight/BMI is beneficial to increase BMD for women regardless of different ages? Does lean mass contribute equally to BMD as does fat mass for women of a wide age range? Is higher percent fat mass beneficial to bone mass in women of different BMI?

6

CHAPTER 2

REVIEW OF LITERATURE Osteoporosis Osteoporosis is a condition characterized by low bone mass and structural deterioration of bone tissue, resulting in bone fragility and an increased susceptibility to fractures, especially of the hip, spine and wrist. One of the main causes of bedridden conditions of the elderly is fracture due to osteoporosis. Osteoporosis is typically diagnosed in the individual when the T-score is 2.5 or more standard deviations below normal (T-score = -2.5 or less) (Kanis, Melton, Christiansen, Johnston, & Khaltaev, 1994). Osteoporosis has become a major public health problem in the U.S. according to the National Osteoporosis Foundation (National Osteoporosis Foundation, 2009). The percentage of women with osteoporosis increases significantly with age from 13% in their 50s to 67% in their 80s (Looker et al., 1997). In generally with every 10% decline in bone mass, the fracture risk doubles (Cummings et al., 1993). In order to prevent osteoporosis, it is necessary to recognize the risks. Age is one of the major risk factors and bone density dramatically drops in women after menopause. Other risks include gender, race and ethnicity, family history of fragility fracture, low body weight/frame size, lack of exercise, as well as inadequate vitamin D and calcium intake (Javaid & Holt, 2008). Certain risk factors cannot be changed; some, however, can be reduced with diet, exercise and altering life style. This project focused on the association between body weight, including lean and fat tissue and bone mass. Normal-weight and BMD The relationship between body weight and/or BMI with bone mass has been documented earlier (Cifuentes et al., 2003; Dawson-Hughes et al., 1987), but a few studies have directly investigated the influence of normal body weight on BMD/BMC. Rico et al. (Rico et al., 2002) found that those who were overweight or obese had a higher total body BMC compared to underweight or normal-weight women regardless of gonadal status with regard to premenopause or postmenopause. This suggested that weight is a more important determinant of bone mass than gonadal status. For women, the decreasing estrogen concentration after menopause is the major cause of the decline in BMD. Recently, Cifuentes et al. (Cifuentes et al., 2003) have shown that

7

postmenopausal women, not on hormone replacement therapy and having a normal- weight had a lower total body BMC than overweight or obese women. Based on many studies in older women, greater BMI is associated with higher BMD (Bauer et al., 1993; Felson, Zhang, Hannan, & Anderson, 1993; Glauber, Vollmer, Nevitt, Ensrud, & Orwoll, 1995; Holbrook & Barrett-Connor, 1993; Kameda et al., 1997), so it is possible that the weight gain in older women may reduce the prevalence of osteoporosis. Furthermore, the influence of total body weight on bone mass is greater at weight- bearing sites such as spine and femurs. Stratifying postmenopausal women by weight (115% or more above ideal body weight) has shown that heavier women have a significantly higher BMC in the spine, hip and radius compared to normal-weight women (Dawson-Hughes et al., 1987). In a study of age-matched obese perimenopausal, postmenopausal and normal-weight women, the obese postmenopausal women had significantly greater vertebral BMD than normal-weight women (Ribot et al., 1987). It must be noted that for this study, obese was defined as having a body weight greater than 10% over normal-weight. These studies support the notion that BMD and BMC, especially at weight-bearing sites, are higher in heavier women regardless of gonadal status. Total body weight is also positively associated with whole body (Reid, Plank et al., 1992), spine (Reid, Ames et al., 1992), and femoral neck BMD (Siris et al., 2001) in premenopausal women suggesting that having a greater body weight protects against bone loss. Losing body weight may result in bone loss and this may increase the incidence of osteoporosis and risk of fractures (Guney et al., 2003; Radak, 2004; Wardlaw, 1996). Thus the correlation between body weight and BMD may be even stronger than the correlation between age and BMD (Slemenda et al., 1990). To date, few longitudinal studies have addressed the effect of weight on the rate of bone loss in women (Brot et al., 1997; Harris, Dallal, & Dawson-Hughes, 1992; Ravn et al., 1999; Tremollieres, Pouilles, & Ribot, 1993). Harris et al.(Harris et al., 1992) carried out a prospective study to assess the influence of body weight on rates of change in BMD in healthy postmenopausal women. They found that women above 106% of ideal body weight had significantly higher BMD in the spine, femoral neck and radius compared to normal-weight women. Although the adjusted mean annual percent loss in BMD and

8

BMC tend to be lower in heavier women, these changes in BMD and BMC were not significant. The absence of significance may be attributed to the fact that the subjects were not heavy enough for the bone loss to become significantly less than in normal- weight women during the two years follow-up period. Similar results were reported by Tremollieres et al. (Tremollieres et al., 1993) who assessed the rate of vertebral bone loss in overweight and normal-weight women. These authors found that women with normal-weight had a significantly lower vertebral BMD at the baseline and an appreciably higher annual rate of vertebral loss for the same follow-up period of time than overweight women. Moreover, baseline urinary calcium excretion was higher in normal-weight women. These results suggest that an increased body weight may have a protective effect and prevent bone resorption. The data from Tremollieres et al. also showed that baseline BMD was positively correlated with both body weight and BMI. A significant positive correlation was found between the annual rate of vertebral bone loss and BMI, but not body weight. These results were in agreement with Ravn et al.’s (Ravn et al., 1999) findings that women in the lowest tertiles of BMI (16-<23) had up to 12% lower baseline spine and hip BMD as compared to those in the highest tertiles (BMI 27-<40). In addition, women with lowest BMI tertiles had approximately a 2-fold greater bone loss at the spine and hip than those with highest BMI tertiles after 2 years follow-up. In addition, women in the lower BMI range had a higher baseline level of urinary calcium. Low bone mass, higher baseline bone turnover and greater bone loss, increases the risk of subsequent development of postmenopausal osteoporosis. Both Ravn and Tremollieres et al.’s studies found that relationship between BMI and BMD was independent of age and years since menopause, which suggests the importance of body weight on BMD. Tremollieres et al. (Tremollieres et al., 1993) suggested that the protective effect of weight on bone is likely to be related to excess adipose tissue. However, given that Tremollieres et al. and Ravn et al. did not measure the body composition, the basis for their conclusion is unclear. Lean and Fat Tissue and BMD in Normal-weight Women Body composition, including lean and fat tissue, is one of the important predictors of BMD although the relative effect of body composition on BMD is still equivocal. Some researchers have proposed that total lean mass is a stronger predictor of BMD,

9

(Chen et al., 1997; Li et al., 2004) whereas others have proposed that total fat mass is related to BMD (Coin et al., 2000; Reid, Ames et al., 1992; Reid, Plank et al., 1992). Others have shown that fat mass and total lean mass are equally associated with BMD (Khosla et al., 1996; Lim et al., 2004). These discrepancies may be explained by the different populations studied, instrumentation methods, skeletal sites evaluated, body composition measurements and the subjects’ body weight. To date, few studies have investigated the effect of body composition on BMD in normal-weight women. In a recent study, Gnudi et al. (Gnudi, Sitta, & Fiumi, 2007) demonstrated that both total fat and lean mass in normal-weight postmenopausal women were positively correlated with total BMC and BMD. Total lean mass had a higher coefficient of correlation with BMD than total fat mass. Ilich-Ernst et al. (Ilich-Ernst et al., 2002) also found that lean mass was a significant predictor in total body BMD, all region of hip, and lumbar spine in slightly overweight perimenopausal women. Douchi et al. (Douchi et al., 2000) showed that total fat mass and total lean mass were both significantly related to lumbar spine BMD in normal-weight premenopausal and postmenopausal women. In a multiple regression, total fat mass and total lean mass were both important determinants of BMD in postmenopausal women, but only total lean mass was an important determinant in premenopausal women. However, no significant difference in total fat mass was observed between premenopausal and postmenopausal women. In a earlier study, the authors not only found that lean mass was the most significant determinant of lumbar BMD but also of total body BMD (Douchi et al., 1997). Several investigators have agreed that lean mass is a better predictor of BMD than fat mass in normal-weight premenopausal women (Winters & Snow, 2000). In addition, a study by Winter et al.(Winters & Snow, 2000) reported that lean mass was a robust predictor for total body, femoral neck, and total hip BMD in premenopausal women. Nichols et al. (Nichols, Sanborn, Bonnick, Gench, & DiMarco, 1995) demonstrated that regional lean mass was a main determinant of BMD at that site. The greater the amount of lean mass in premenopausal women, the greater the BMD (Sowers, Kshirsagar, Crutchfield, & Updike, 1992). In a 12-year longitudinal study, researchers found that a change in lean mass over the 12-year follow-up period, but not a change in fat mass was a significant determinant of proximal femur BMD in normal-weight premenopausal

Full document contains 104 pages
Abstract: Purpose. The purpose of this study was to investigate the relationships between body composition (fat and lean mass), body weight, body mass index (BMI) and bone mineral density (BMD) and bone mineral content (BMC) in women across the age span. Methods. 1046 healthy Caucasian women (49.9 ± 15.9 years old) were recruited and categorized to four age groups, ranging from 18 to 35 years old, 35 years to before the age of menopause, menopause to 65 years and over 65 years old. Each different age group was further categorized according to subjects' body mass index (BMI < 25, BMI = 25-29.9, and BMI ≥ 30). Measurements included anthropometrics, body composition and BMC/BMD by dual-energy x-ray absorptiometry (DXA). Results. Subjects in the younger groups were taller, weight less and had greater total body BMC/BMD and BMD at spine, femoral neck, and total femur (p <0.05) compared with older subjects. Obese women had higher total lean and fat mass, and the highest BMD/BMC in all skeletal sites (p <0.05) among different age groups. Weight, BMI, total lean, and total fat mass were positively correlated with total body BMC/BMD, BMD of all skeletal sites among different age groups. The results from multiple linear regression models revealed that weight was a significant predictor of total body BMC/BMD, BMD of all skeletal sites in women of different age groups, gonadal status, and different BMI, except overweight women. Both lean and fat mass were important determinants of total body BMC/BMD, BMD at femur and forearm in premenopausal women though total lean mass had greater effect than total fat mass. Total fat mass was the only significant predictor of total body BMC/BMD, BMD at other sites in postmenopausal women. Furthermore, total fat mass became more important with the increased body weight. Further analysis of covariance in subjects stratified by body weight and percent body fat revealed that high percent body fat seemed to have negative effect on bone mass in total body BMC/BMD and BMD at spine, femoral neck and forearm when mechanical loading effect of body weight was controlled. Conclusions. These results show that overweight/obese women had higher BMD in all skeletal sites than normal-weight women. Lean mass was an important predictor of BMD in premenopausal women and fat mass became more important in postmenopausal women. Higher fat mass however, may not have beneficial effect on bone mass when mechanical loading of weight is accounted for.