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15-08-2011 | Bone health | Article

Low BMD, impaired bone microarchitecture present in amenorrheic athletes

Abstract

Free abstract

MedWire News: Young amenorrheic athletes (AA) have low bone mineral density (BMD) and impaired bone microarchitecture, despite undertaking weight-bearing exercise, compared with eumenorrheic athletes (EA) and non-athletes, show US study findings.

The results are of importance, given that abnormal bone microarchitecture is an independent predictor of fracture risk, especially during a critical time of bone accrual, say the researchers.

"Our study demonstrates for the first time the differing impact of athletic weight-bearing activity versus amenorrhea (and associated estrogen deficiency) on bone microarchitecture in adolescent and young athletes," report Madhusmita Misra (Massachusetts General Hospital and Harvard Medical School, Boston) and co-authors.

For the study, the team compared BMD and bone microarchitecture in 16 AA, 18 EA, and 16 non-athletes using dual-energy X-ray absorptiometry and high-resolution peripheral quantitative computed tomography.

There were no significant differences between the groups in terms of bone age, body mass index, vitamin D levels, or age (15-21 years).

Compared with EA and non-athletes, AA had significantly lower BMD scores (0.82-0.95 g/cm2 vs 0.91-1.06 g/cm2 and 0.83-1.01 g/cm2, respectively) and BMD Z-scores (-1.66 vs -0.62 and -0.36, respectively).

However, EA had significantly higher femoral neck and hip BMD Z-scores compared with AA and non-athletes, at 0.21 versus -0.64 and -0.62, and 0.80 versus -0.36 and -0.41, respectively. These differences remained significant after controlling for bone age and height.

Bone microarchitecture analysis showed that at the weight-bearing tibia, both groups of athletes had greater total area, trabecular area, and cortical perimeter than non-athletes. Cortical area, total density, and thickness were lower among AA.

The researchers suggest that the higher tibial cortical area seen in EA versus AA and non-athletes may be due to the cortical perimeter expanding outward in weight-bearing bone secondary to exercise, whereas expansion of the endocortical circumference is prevented by estradiol.

In contrast, greater total area and cortical perimeter were not observed in athletes at the ultradistal radius, a non-weight bearing site. "This suggests that forces exerted on the tibia through weight-bearing exercise likely contribute to increased total cross-sectional area in athletes," say the researchers.

Furthermore, AA had lower trabecular numbers and higher trabecular separation compared with EA and non-athletes. After controlling for bone maturity, nutritional status, and lean mass, grouping accounted for 18-24% of the variability in tibial trabecular number and separation.

Regression analysis revealed that menarchal and bone age were significant predictors of total bone density, contributing to 44% and 40% of the variability at the radius and tibia, respectively. Indeed, later menarchal age was an important determinant of impaired microarchitecture.

"Independent of BMD, microarchitecture provides information about bone parameters in the amenorrheic athlete," write the authors in the Journal of Clinical Endocrinology and Metabolism.

MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Ingrid Grasmo

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