In this examination of the relationships of disordered-eating attitudes and behaviors with BMD and markers of bone turnover, we found a positive relationship between interview assessment of weight concern and urine free cortisol, a biological marker of stress. Additionally, we found that shape concern, but not cognitive restraint, was inversely associated with lumbar spine BMD. Since the field is still uncertain as to whether questionnaire or interview is a more valid assessment of disordered-eating in adolescents [10
], we included both measures in order to assess for any methodological differences in findings. Furthermore, since the extant adult literature examining bone health in relation to restraint utilized solely questionnaire methods, we believe it is important to include both questionnaire as well as interview measures. Our findings revealed that only weight and shape concerns, as assessed by interview, but not by questionnaire, were predictive of markers related to bone health.
In contrast to studies of healthy pre-menopausal women and overweight women, [1
] we found no relationship between adolescents’ cognitive dietary restraint and BMD, serum osteocalcin, or urine free cortisol. We did, however, find a positive association between weight concern and urine free cortisol. As suggested in the adult literature [1
], we speculate that the stress of maintaining undue concern with one’s weight may be a cause of increased endogenous cortisol excretion. Cortisol is a physiological marker of stress and has been shown to impede osteoblast replication [1
Studies in adults have found that depression is negatively associated with BMD [14
, 41]. One such study reported elevated levels of urine free cortisol in pre-menopausal women with major depressive disorder or depressive symptoms [35
]. However, we found no significant relationship between depressive symptoms and cortisol or markers of bone turnover. This finding may be, in part, due to the relatively healthy psychological profile of participants. The cutoff score for clinical depression on the CDI is 19 out of 54 [25
], while the mean CDI score for our sample was 7.4 and only 8 subjects had values above 19. Since the mean depression score for our sample was relatively low, it seems unlikely that depression served as an important factor in the levels of cortisol or BMD found in our analyses.
Another potential physiologic mediator of the effect of restraint and disordered eating on bone health is Peptide YY (PYY) which has been shown to be elevated in anorexia nervosa, and inversely correlated with BMD [36
]. Although this relationship may be due to the inverse relationship between PYY and BMI, the role that PYY plays in the impact of restraint and eating pathology on BMD warrants further exploration.
Since our sample consisted entirely of treatment-seeking, overweight youth, it is possible that cognitive eating restraint was somewhat less pathological among this sample. Since restraint may actually be beneficial to individuals attempting to lose weight, concern with weight may be a more salient stressor than restraint to our studied group, thereby accounting for the positive association with cortisol. Bolstering this possibility are data suggesting that dietary restraint is common among overweight individuals [6
]. The finding that shape concern, but not cognitive restraint, was a significant contributor to the model predicting lumbar spine BMD further suggests that among severely overweight adolescents, dissatisfaction with shape and importance of shape in self-evaluation, may be a more relevant stressor than cognitive dietary restraint.
Exclusive of eating patterns, data regarding the relationship between overweight status and bone health are conflicting. De Schepper et al. found that overweight status during adolescence had no negative effect on BMD [37
], while other studies have found that overweight children present with increased total body BMC [38
], and BMD [39
] compared to non-overweight peers. By contrast, other data suggest that overweight is associated with lower BMD Z-scores among children ages 5–19y who have experienced at least two fractures of the forearm [40
]. Our data indicating that psychological distress from disordered-eating patterns may influence bone density in overweight adolescents, independent of body weight, may help explain these contradictory findings.
Strengths of this study include the use of both interview and questionnaire methods to assess eating-disordered psychopathology and the measurement of BMD by DXA, considered to be an excellent measure of BMD. Moreover, the studied sample was relatively large, racially diverse and included both males and females. A study limitation includes the usage of a questionnaire-measure of depressive symptoms as opposed to a diagnostic interview. Our findings are also limited in that they may only be generalizable to samples of weight-loss treatment-seeking overweight adolescents. Another limitation is that a number of models were tested (in order to avoid issues of multicollinearity), which increases the likelihood of Type 1 error. However, analyses were planned a priori and were similar to findings from previous data. Finally, a notable limitation is the cross-sectional nature of our study. Future longitudinal studies investigating the effects of eating pathology on bone health and markers of bone turnover are required.
In conclusion, our findings corroborate previous studies demonstrating that disordered-eating attitudes may be closely linked with an increase in endogenous cortisol production and a decrease in BMD. Our data suggest that underlying psychological distress, rather than merely dietary restraint, may be the primary contributor to these associations. However, the exact mechanism by which this distress may predispose individuals to decreased BMD remains unclear.
Adolescence is a crucial time during which to study bone health; the literature has shown that 90% of adult bone mass is acquired before the age of 20 [14
]. Furthermore, disordered-eating attitudes and restraint have been shown to emerge primarily during adolescence [15
]. Thus the relationship between eating pathology and bone health in adolescent samples seems to warrant extensive investigation.
Further study is required to determine the most relevant aspects of disordered-eating for bone health in adolescents, and whether such constructs are prospectively predictive of the physical outcome of overweight youth.