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Original Studies |
Address all correspondence and requests for reprints to: Jorunn Sundgot-Borgen, Ph.D., University of Sport and Physical Education, P.O. Box 4014, Ullevål Hageby, 0806 Oslo, Norway. E-mail: jorunn{at}brage.idrettshs.no
| Abstract |
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| Introduction |
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A number of studies have shown that healthy athletes have better than average bone mass, and that exercise increases bone mineral density (BMD) (3, 4, 5, 6, 7, 8). On the other hand, amenorrheic athletes have been shown to have vertebral BMD values 931% lower than those of eumenorrheic women (7). Lloyd et al. (6) found that collegiate athletes who missed more than 50% of their expected menses had vertebral densities that were 69% those of normally menstruating athletes. Rutherford (7) also found a significantly lower lumbar and total spine BMD in amenorrheic vs. eumenorrheic athletes, but these two groups did not differ in total body BMD.
Amenorrhea is one of the diagnostic criteria for anorexia nervosa, but it is not a diagnostic criterion for bulimia nervosa (1). However, menstrual irregularities are described in about 50% of women with bulimia nervosa (9).
Many anorectic patients have asymptomatic osteopenia, and some develop fractures (10, 11, 12, 13, 14, 15). However, results of the effects of exercise on bone mass in anorectic patients are conflicting. Rigotti et al. (14) reported that anorectics who were highly active had greater radial cortical bone density than those who were less active. Joyce et al. (13) found in their anorectic patients that moderate exercise was protective, whereas strenuous exercise was detrimental to bone mass. Bachrach et al. (16, 10) and Kooh et al. (17) reported no relationship between bone mass and exercise in their anorectic patients. The discrepancy between these studies could be explained by a lack of control for exercise history, training volume, and type of training.
There is little information available on changes in BMD in subgroups of patients with eating disorders (18). The division of anorexia nervosa into food-restricting and bulimic subtypes, and the proposed division of bulimia into subgroups have been accepted in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (1). Just as the psychiatric course of the illness differs between subgroups of eating disorders, so may the medical complications, such as a reduced bone mass. Therefore, the aims of this study were to examine BMD and to examine the association among exercise, menstrual function, and BMD in different groups of patients with eating disorders.
| Subjects and Methods |
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Physicians and psychologists in private practice and psychiatric out-patient clinics in the Oslo area were invited by letter to refer eating disorder patients to the study. Patients who met the DSM-IV criteria for anorexia nervosa (without a history of bulimia) or bulimia nervosa (without a history of anorexia nervosa), who had no other psychiatric or somatic disorders that could have triggered the eating disorder, who had not been receiving treatment for eating disorders during the last 6 months, who did not use any medication, who were motivated for treatment, and who were between 1829 yr of age were potential subjects.
Fourteen of the 70 patients referred did not meet the inclusion criteria and were therefore not included in the study. The reason for excluding these patients were history of other eating disorders (n = 4), additional personality disorders (n = 3), use of medication (including birth control pills; n = 5), and involvement in treatment during the last 6 months (n = 2). In all, 56 patients (13 anorectic and 43 bulimic) were included in the study.
The need for a control group in this study was announced at an
information board at the University of Oslo. The following inclusion
criteria were listed in this announcement: eumenorrhea, regular
participation in weight-bearing exercise (12 h/week) in addition to
the mandatory 23 h/week of the mandatory physical education lesions
from age 718 yr, no history of somatic or psychiatric disorders, no
use of medication (including birth control pills), and willingness to
complete a dietary registration, a fitness test, a medical exam,
clinical interviews, and measurement of bone mass and tissue fat.
Twenty-five signed up for the study, but 8 were excluded due to
symptoms of eating disorders (n = 3), menstrual irregularities
(n = 2), vegetarian dietary habits (n = 2), and competitive
running (n = 1). Thus, 17 healthy females were included in the
control group. These students matched the patients by age and the body
weight of the bulimics (Table 1
). No attempt was made to find students
who could match the anorectic patients in weight.
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Interview and clinical examination
All patients and controls underwent a clinical examination, including an interview and physical examination. Body weight and height were recorded with subjects wearing underwear and no shoes. Body mass index (BMI) was calculated as the body weight (kilograms) divided by the squared height (meters).
The interview protocol was developed as part of the Diagnostic Survey for Eating Disorders (21) and has been described previously (20). DSM-IV criteria (1) were used to define anorexia nervosa and bulimia nervosa. For consistency, each examination or interview was conducted by the same researcher.
Menstrual dysfunction
The subjects were classified according to their menstrual history (menstrual function during the period since developing an eating disorder) and menstrual status (the number of cycles during the last 12 months). Eumenorrhea was defined as menstrual cycles of less than 35 days, but longer than 23 days (22). Menstrual dysfunction was defined as secondary amenorrhea (lack of more than three consecutive cycles) or oligomenorrhea (menstrual cycles of between 3590 days).
Assessment of previous and present physical activity
Previous physical activity pattern (since onset of symptoms) and present training volume (including the average number of training hours per week during the last 12 months) were assessed by a self-report questionnaire followed by an interview to improve accuracy. The questionnaire included information on all activities common for children, teenagers, and young adults in Norway. Questions about frequency and regularity (in addition to the mandatory physical education lessons) from age 12 yr were included.
For part of the analysis the subjects were divided into 3 different groups depending on their reported degree of exercise regularity since the onset of their eating disorder (except for the last 6 months): regular, intermittent, and sedentary. Regular exercise was defined as weight-bearing aerobic exercise for at least 2 h/week. Intermittent was defined as more or less regular weight-bearing exercise (never exercising regularly for >2 months). The sedentary group included those who did not exercise during their illness. Six of 18 subjects in the sedentary group had not participated in mandatory physical education lesions since the onset of symptoms.
Fitness assessment
Aerobic capacities were expected to vary widely. Therefore, peak oxygen uptake was assessed using a walking test. A modified Balke protocol (23) was used. The major modifications were as follows: the participants warmed up for 10 min, and the inclination of the treadmill was increased every minute, not every second minute. The test was terminated when the participants were close to exhaustion according to the Borg scale (>18) or when the oxygen uptake leveled off and the respiratory exchange ratio was above 1.05.
BMD and fat mass tissue assessment
BMD and soft tissue composition of the total body and major subregions were measured with dual energy x-ray absorptiometry (DXA; Lunar DPX-l, Lunar, Madison, WI). For the purpose of this study, the BMD values of the lumbar vertebrae (L2L4), femoral neck, and total body were measured. From the total body scans, the BMDs of the arms and legs could be evaluated separately. Fat mass as a percentage of total body mass was calculated from the total body scans. In our laboratory, the reproducibility of the DXA measurements were as follows: L2L4, 1.0%; femoral neck, 2.5%; total body, 0.7%; and percent fat, 1.9%. The reproducibility was estimated by scanning 25 middle-aged women twice within 2 weeks.
Statistical analysis
All analyses were performed using SPSS software (SPSS, Evanston, IL). Differences between more than two groups were determined by one-way ANOVA (Kruskal-Wallis) and Students t test between pairs of groups for continuous ordinal variables. Pearsons correlation test was employed to determine the association between continuous variables. All tests were two tailed. Contingency table were used to test for association between categorical variables. Stepwise linear regression was used to determine how the dependent (response) variable (BMD) changed as a function of the independent (explanatory) variables: duration of eating disorders, body weight, BMI, peak oxygen uptake, tissue fat, menstrual history, and exercise history. P < 0.05 was considered statistically significant. Results are presented as the mean and SD unless otherwise noted.
| Results |
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Physical exercise
Sixty-six percent of the eating disorder patients and 61% of the
controls were physically active in addition to mandatory physical
education classes before the age of symptom debut (mean, 16 yr; range,
1321 yr). There was no difference between the regularly exercising,
intermittent, and sedentary bulimic groups with respect to physical
activity before developing symptoms of eating disorders. After onset of
symptoms, a significantly higher proportion of anorectic patients
exercised on a regular basis, had a higher current training volume, and
had a higher peak oxygen uptake than the bulimic and control groups
(Table 2
).
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Menstrual history and status
All anorexia nervosa patients had been amenorrheic since the start of their eating disorders. A history of menstrual irregularity was reported by 68% of the bulimic patients (14 amenorrheic and 16 oligomenorrheic), and 74% (15 amenorrheic and 17 oligomenorrheic) reported menstrual irregularities within the last 12 months. In the bulimic group, the menstrual histories of the different bulimic groups were as follows: regular exercisers, 6 amenorheic, 6 oligomenorrheic, and 1 eumenorheic; intermittent exercisers, 5 amenorheic, 2 oligomenorrheic, and 5 eumenorheic; and sedentary, 3 amenorheic, 8 oligomenorrheic, and 7 eumenorheic. None of the controls had a history of menstrual dysfunction.
BMD
BMD was significantly lower in the anorectic group compared
with the those in the bulimic and control groups for all
regions examined, including total body BMD (P < 0.01;
Table 3
).
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In the univariate correlation analysis for the bulimic group, an
association was found between lumbar BMD and exercise history, peak
oxygen uptake, BMI, tissue fat, and menstrual dysfunction
(P < 0.010.05). After adjusting for correlation
between explanatory variables, only exercise history, peak oxygen
consumption, BMI, and tissue fat were associated with lumbar BMD
(P < 0.010.05; Table 5
). Of the total variance, 86% could be
explained by these variables. The same trend was found for the other
skeletal regions studied.
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| Discussion |
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It should be noted that although the anorectics in our study had been excessive exercisers since the onset of the eating disorder, 9 of 13 anorectics had BMD values more than 2.5 SD below control values, which corresponds to the WHOs definition of osteoporosis. The anorectic group had lumbar BMD values that were 65% of control values and significantly lower values than bulimics and controls in all regions studied; there was no trend toward higher values in weight-bearing regions. This supports other recent studies with amenorrheic athletes, indicating that the deficit appears to be generalized throughout the skeleton (24, 25, 26).
Rigotti et al. (14) reported that anorectics who were highly active had greater radial cortical bone density than those who were less active. Furthermore, Joyce et al. (13) studied groups of anorectics who also exercised at various levels (<1 to >6 h/week). All of their subjects demonstrated a significant decreased vertebral BMD compared with normal values. In contrast to the results from Rigottis study (14), the results from our study show that anorectics are not able to maintain normal bone mass even if they exercise regularly. Therefore, the combination of a high volume of exercise combined with malnutrition, abnormal cortisol secretion (27), and estrogen deficiency (13) may explain the decrease in BMD in these subjects.
As expected, bulimic patients who were defined as intermittent exercisers overreported both the degree of regularity and the number of training hours per week. Bulimic patients who did not exercise regularly or were sedentary seem to follow their bulimic eating pattern (28). This overreport of exercise should be kept in mind for those treating bulimic patients. The relatively low correlation between peak oxygen uptake and the reported hours of exercise per week could be explained by differences in genetics, training methods, and nutritional status (29). In addition, the average time since onset of symptoms for the bulimic patients was 5.7 (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14) yr, indicating that some of these patients were too exhausted to keep the intensity needed to maintain or enhance their aerobic capacities.
Bulimics who had been exercising regularly or periodically since acquiring the eating disorder had higher lumbar spine BMD than sedentary bulimics and anorectic patients in weight-bearing skeletal sites. However, there was no difference in arm BMD between exercisers and nonexercisers. The difference observed in the effects of exercise on BMD between bulimic and anorectic patients could be explained by the suggestion made by Koch et al. (17) that nutritional deprivation may have a more deleterious effect on bone than either the duration of amenorrhea or the serum levels of sex hormones.
The eating disorder patients in this study who had been performing aerobic dancing and jogging more or less regularly during the eating disorder history may have benefited from the mechanical stress placed on the different weight-bearing skeletal regions measured (lumbar spine, femural neck, and legs). It is therefore not surprising that there was no exercise effect for arm BMD. The DXA method used for determining BMD in this study averages BMD for the entire extremity. It may be that differences would have been found if specific sites in the lower leg had been examined as well. This is supported by the finding that the bulimic patients with the highest L2L4 BMD values had the highest degree of regularity in their exercise history and the highest number of training hours per week. Furthermore, the groups with the higher BMD values also had higher percentages of fat tissue.
In contrast to previous findings indicating that trabecular bone is not protected by exercise (6, 7, 12, 13, 30), results from this study indicate that there is an exercise effect for bulimic patients. Therefore, it may be that hormonal imbalance is not the major factor explaining reduced bone mass in sedentary bulimic patients. As anorectics and bulimic patients both have menstrual dysfunction, it is tempting to argue that the energy intake and contents plays significant roles. Although menstrual dysfunction was associated with bone mass, it was not one of the variables in the multiple regression model explaining reduced bone mass in the bulimic groups.
Most researchers (2, 6, 19) report that prior menstrual history is the best predictor of current BMD and that women with a history of amenorrhea have lower BMD than those who have always been cyclic. On the other hand, it has been reported that not all physically active females suffering from menstrual dysfunction have low bone mass (4, 5, 31). Their skeletal status depends upon the length and severity of the menstrual irregularity as well as factors that influence their BMD before the onset of menstrual dysfunction: type of skeletal loading during activity, nutritional status, and genetic components (5).
The established difference in energy and nutrient intake between active anorectic and bulimic patients (28) could partly explain why exercising bulimics, in contrast to the anorexics, may experience the positive effect of weight-bearing exercise (aerobic dancing and jogging) on bone mass.
It is interesting to note that there appeared to be no difference in BMD within the different exercise subgroups of bulimic patients when they were separated based on menstrual function or history. Again, more data are needed to determine whether mechanical stress and weight-bearing exercise can effectively prevent or attenuate bone loss at specific skeletal sites in normal weight, eating disorder patients with menstrual dysfunction. More research is needed in many areas related to women, exercise, nutrition, and bone mass. Prospective longitudinal studies should include females at different ages, with diverse activity histories (type and volume), representing the total spectrum of weight, eating disorders, and menstrual function.
Received September 18, 1997.
Revised May 12, 1998.
Accepted May 19, 1998.
| References |
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This article has been cited by other articles:
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S. Naessen, K. Carlstrom, R. Glant, H. Jacobsson, and A. L. Hirschberg Bone mineral density in bulimic women - influence of endocrine factors and previous anorexia. Eur. J. Endocrinol., August 1, 2006; 155(2): 245 - 251. [Abstract] [Full Text] [PDF] |
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J. M. Beiseigel and S. M. Nickols-Richardson Anthropometrics, Bone Mineral Density, and Dietary Intake in a Group of Young Adult Females Family and Consumer Sciences Research Journal, March 1, 2002; 30(3): 404 - 423. [Abstract] [PDF] |
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S. Zipfel, M. J. Seibel, B. Lowe, P. J. Beumont, C. Kasperk, and W. Herzog Osteoporosis in Eating Disorders: A Follow-Up Study of Patients with Anorexia and Bulimia Nervosa J. Clin. Endocrinol. Metab., November 1, 2001; 86(11): 5227 - 5233. [Abstract] [Full Text] [PDF] |
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T.M. O'CONNOR, D.J. O'HALLORAN, and F. SHANAHAN The stress response and the hypothalamic-pituitary-adrenal axis: from molecule to melancholia QJM, June 1, 2000; 93(6): 323 - 333. [Abstract] [Full Text] [PDF] |
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