Journal Title (Medline/Pubmed accepted abbreviation): Int J Sport Nutr Exerc Metab
Page numbers: 418-426
doi (if applicable): N/A
Summary of Background and Research Design
Background:Studies have shown that physical activity can help maintain and actually increase bone-mineral density (BMD). However, low BMD has been recognized in female athletes who participate in sports that emphasize leanness, such as gymnastics and endurance training. Low BMD is associated with menstrual dysfunction and negative energy balance in the female athlete triad. There have been several longitudinal studies assessing BMD in non-elite athlete groups, but there have been no multi-year longitudinal studies in elite athletes.
Hypothesis/purpose of study: To compare the distribution of BMD in female UK elite endurance runners with the parameters established in healthy nonathletic woman, determine BMD, and assess the associations between BMD, menstrual status, disordered eating, and training hours.
Subjects:Forty-four elite endurance female runners (mean ± standard deviation: age 22.9 ± 6.0 years, weight 52.8 ± 4.8 kg, height 1.66 ± 0.1 m, body mass index 19.1 ± 1.5) participated in a cross-sectional study, and 7 (mean ± standard deviation: age 22.0 ± 4.8 years) provided longitudinal data.
Experimental design:Longitudinal, cross-sectional observational study
Treatments and protocol:BMD of the total body, anteroposterior L2-4 vertebrae, anteroposterior femoral neck, and dominant-arm distal radius were measured by dual-X-ray absorptiometry (DXA). BMD (g/cm2) and Z scores were collected for analysis. All athletes attending for DXA scan completed 2 questionnaires. The first measured training and menstrual history and the second (the Three-Factor Eating Questionnaire, TREQ-R18) was used to describe eating behavior, in particular cognitive restraint patterns. Training history was assessed by recording the number of hours spent training per day during a normal training week. Current menstrual status was obtained from the reported numbers of menses in the preceding 12 months according to 3 categories: eumenorrheic (> 10 cycles/year), oligomenorrheic (4 to 9 cycles/year), or amenorrheic (0 to 3 cycles/year). Current use of oral contraceptive pills was recorded. All questionnaires were completed in person at the time of DXA scanning.
Summary of research findings:
- Cross-sectional analysis (N = 44)
- Low BMD (Z = -1 to -2 SD) in the athletes was noted in 4.9% (n = 2) for the total body, 34.2% (n = 14) at the lumbar spine, 13.8% (n = 4) at the femoral neck, and 29.6% (n = 13) at the radius.
- Prevalence of osteoporosis (Z < -2 SD) was 7.3% (n = 3) at the lumbar spine and 33.3% (n = 9) at the radius, but was 0% for total body and femoral neck.
- There were no significant differences in Z score at each of the 4 assessment sites between the 3 menstrual status groups.
- There were no significant correlations between BMD Z scores at each of the 4 assessment sites and number of hours training per week.
- There were no significant correlations between cognitive restraint, uncontrolled eating, or emotional eating scale scores and BMD Z scores at the 4 assessment sites.
- Longitudinal analysis (n = 7)
- Menstrual status was shown to have no significant effect on the rate of loss of BMD. However, a trend was demonstrated between higher rates of BMD loss at both the total body (P = .064) and radius (P = .063) in the oligo-/amenorrheic group.
- There was a significant negative correlation between increased hours of training per week and a change in BMD at L2-4 (P = .026, r = -0.87, n = 6).
- A high emotional eating score was positively correlated with changes in lumbar-spine BMD (P = .038, r = 0.71, n = 7). There were no further significant correlations between cognitive restraint, uncontrolled eating, or emotional eating scale scores and regional BMD.
Interpretation of findings/Key practice applications:
The authors stated that, to their knowledge, this is the first longitudinal study to examine the relationship between BMD, menstrual status, disordered eating and training volume in elite female athletes. Low BMD was observed in 34.2% of the athletes at the lumbar spine and osteoporosis in 33% at the radius. In cross-sectional analysis, there were no significant relationships between BMD and the possible associations. Menstrual dysfunction, disordered eating, and low BMD were, however, coexistent in 15.9% of athletes. This study verifies the presence of aspects of the female athlete triad in elite female endurance athletes and notes a substantial prevalence of low BMD and osteoporosis. Although the evidence offered by this study provides important insights, the study has some limitations. The use of self-report questionnaires for collecting data on training status, menstrual status, and eating patterns may be a source of bias. In addition, the sample sizes for both the cross-sectional study (n = 44, 23 of whom were oligo- or amenorrheic) and the longitudinal study (n = 7) are probably too small to permit definitive conclusions on the effects of menstrual status on BMD loss. It is interesting, however, that even with this small sample size in the longitudinal study, there were trends toward increased BMD loss for both the whole body and radius in the oligo-/amenorrheic group. This study also aimed to compare the distribution of BMD in elite endurance runners with the parameters established in healthy nonathletic women, but no such comparison was done. This should be considered pilot work that suggests that further longitudinal studies are needed in this field.