Energy balance and bone mineral density on male and female distance runners

Reports of lumbar spine (IS) skeletal deficits in female athletes with menstrual disorders are common, although it is not clear whether the deficits are confined to this group. The main factor presumed to be responsible is oestrogen deficiency characterised by amenorrhoea, however emerging evidence indicates that energy deficiency can also disturb bone turnover. This thesis aimed to determine
whether male distance runners are at a comparable risk for bone loss and whether there was a relationship between reported energy balance and BMD. Methods 109 distance runners (18-50 years) participated (65 females, 44 males). A questionnaire assessed menstrual status, performance level and training characteristics. 7-day dietary and exercise records were used to quantify energy balance. LS, dual femur (DF) and total body (TB) BMD were measured using dual-energy X-ray absorptiometry. Bone size was accounted for: bone mineral apparent density (BMAD =BMD / ...JBonearea. Results Male and female IS T-scores were similar (-0.8, -0.8). 41.6% of female and 36.4% of male runners were osteopenic (LS). Age, BMI and
body fat- adjusted LS T-scores were lower in male than female runners (p<0.05). Adjusted LS T-scores were lower in male compared to eumenorrhoeic runners (p<0.01). Female runners who used the oral contraceptive pill had similar BMD to amen/oligo-menorrhoeic runners, which were significantly lower than eumenorrhoeic runners (p<0.01). These runners were also more energy deficient (p<0.01). Elite runners had greater energy deficits, lower IS T-scores, BMAD and a smaller bone area than club runners (p<0.001). DF and TB T-scores were normal, did not correlate
with weekly mileage and after adjustment for calcium intake, did not correlate with energy balance. IS T-score negatively correlated with stress fracture incidence
(p<O.OOOI).Most runners were energy deficient and the severity of energy deficiency correlated with lower BMI and body fat. Energy balance was the strongest predictor
of LS BMD and T-scores, Conclusions Low LS BMD in distance runners is not gender-specific; the oral contraceptive pill may be insufficient to protect against bone loss in female runners and elite runners may be more at risk of bone fragility. Energy deficit was the underlying determinant of low BMD in male and female runners, emphasising the importance of energy balance for bone health.