OR32-05 Lower Oxytocin Levels Are Associated with Lower Bone Mineral Density and Less Favorable Hip Geometry in Hypopituitary Men

Introduction: Hypopituitary patients are at risk for bone loss. Oxytocin (OT) and vasopressin (VP) are hypothalamic-posterior pituitary hormones with opposing actions on bone (anabolic and catabolic, respectively). Whether OT and/or VP contribute to impaired bone homeostasis in hypopituitarism is unknown. Hypothesis: We hypothesized that lower plasma OT and higher VP levels would be associated with lower bone mineral density (BMD) and less favorable hip geometry and estimated strength in men with hypopituitarism. Design: We performed a cross-sectional study of 37 men with hypopituitarism ages 20–60 (mean±SEM 45.8±1.9) years: 20 with anterior pituitary deficiencies only (APD) and 17 with central diabetes insipidus (CDI; marker of posterior pituitary dysfunction), of similar age, body mass index and number of adenohypophyseal deficiencies, on stable hormone replacement. Main outcome measures were fasting plasma OT and VP levels, and dual X-ray absorptiometry-derived BMD (lumbar spine, total hip, femoral neck, distal radius and subtotal body) and hip structural analysis (HSA; cortical thickness, section modulus, and buckling ratio at narrow neck, intertrochanteric region and femoral shaft). All analyses were adjusted for multiple comparisons using Holm-Bonferroni correction. Results: Mean BMD Z-scores were lower at all sites and all HSA parameters at the intertrochanteric region as well as cortical thickness at the femoral shaft were less favorable in those participants who had fasting OT levels below the median than in those with higher levels (P≤0.022). There were no differences in any bone variables at any skeletal site in those with fasting VP levels below vs. above the median (P≥0.232). Lower fasting OT levels were positively associated with (1) lower BMD Z-scores at the lumbar spine, femoral neck, total hip and subtotal body (P≤0.02) and (2) less favorable hip geometry and strength variables (lower cortical thickness, lower section modulus and higher buckling ratio) at the intertrochanteric region in CDI (P≤0.018), but not APD participants (P≥0.458 and P≥0.429, respectively). The associations between OT and bone variables remained significant after adjusting for key determinants of BMD including lean body mass and IGF-1 levels. There were no relationships between plasma VP levels and bone variables in CDI or ADP groups (P≥0.173). Conclusions: OT, but not VP levels, are positively associated with BMD at multiple sites as well as favorable hip geometry and estimated strength in men with hypopituitarism and CDI. Future studies will be important to determine whether OT could be used therapeutically to optimize bone health in patients with hypopituitarism.

Structural Strength Benefits Observed at the Hip of Premenarcheal Gymnasts Are Maintained Into Young Adulthood 10 Years After Retirement From the Sport

Purpose: Premenarcheal female gymnasts have been consistently found to have greater bone mass and structural advantages. However, little is known about whether these structural advantages are maintained after the loading stimulus is removed. Therefore, the purpose of this study was to investigate the structural properties at the hip after long-term retirement from gymnastics. Methods: Structural properties were derived from dual-energy X-ray absorptiometry scans using the hip structural analysis program for the same 24 gymnasts and 21 nongymnasts both in adolescence (8–15 y) and adulthood (22–30 y). Structural measures were obtained at the narrow neck, intertrochanter, and femoral shaft and included cross-sectional area, section modulus, and buckling ratio. Multivariate analysis of covariance was used to assess differences between groups in bone measures while controlling for size, age, maturity, and physical activity. Results: Gymnasts were found to have structural advantages at the narrow neck in adolescence (16% greater cross-sectional area, 17% greater section modulus, and 25% lower buckling ratio) and 14 years later (13% greater cross-sectional area and 26% lower buckling ratio). Benefits were also found at the intertrochanter and femoral shaft sites in adolescence and adulthood. Conclusion: Ten years after retirement from gymnastics, former gymnasts’ maintained significantly better hip bone structure than females who did not participate in gymnastics during growth.

The Influence of Serum Uric Acid on Bone Mineral Density, Hip Geometry, and Fracture Risk: The Rotterdam Study

Context: The role of uric acid (UA) in skeletal metabolism remains to be unraveled. Objective: We prospectively investigated the association between UA, bone mineral density at the femoral neck (FN-BMD), hip bone geometry parameters, and incident fracture risk and examined whether the associations were modified by age and vitamin C intake. Participants and Setting: Data of 5074 participants of The Rotterdam Study, a prospective population-based cohort. Exposure: Serum UA was assessed at baseline. Main Outcomes and Measures: FN-BMD was measured at baseline, and at second, third, and fourth visits of the Rotterdam Study. Hip bone geometry parameters were measured at baseline and at the second and third visits. Results: Serum UA levels (per SD increase) were positively associated with FN-BMD (β = 0.007 g/cm2; 95% confidence interval [CI] = 0.002–0.01), thicker cortices (β = 0.002 cm; 95% CI = 0.0003–0.002), lower bone width (β = −0.013 cm; 95% CI = −0.23 to −0.003), and lower cortical buckling ratio (β = −0.19; 95% CI = −0.33 to −0.06). The effects of UA on FN-BMD and cortical buckling ratio tended to become stronger over time. Hazard ratios and 95% CIs per SD increase of baseline UA levels for the development of any type of incident fractures, nonvertebral fractures, and osteoporotic fractures were 0.932 (0.86–0.995), 0.924 (0.856–0.998), and 0.905 (0.849–0.982), respectively. These associations were more prominent in older individuals (age, >65 y) and in participants with high intakes of vitamin C (> median). Conclusions: Higher levels of serum UA are associated with higher BMD (at the expense of thicker cortices and narrower bone diameters) and may be a protective factor in bone metabolism. However, interactions with age and vitamin C may be present.

The Influence of Organized Physical Activity (Including Gymnastics) on Young Adult Skeletal Traits: Is Maturity Phase Important?

We prospectively evaluated adolescent organized physical activity (PA) as a factor in adult female bone traits. Annual DXA scans accompanied semiannual records of anthropometry, maturity, and PA for 42 participants in this preliminary analysis (criteria: appropriately timed DXA scans at ~1 year premenarche [predictor] and ~5 years postmenarche [dependent variable]). Regression analysis evaluated total adolescent interscan PA and PA over 3 maturity subphases as predictors of young adult bone outcomes: 1) bone mineral content (BMC), geometry, and strength indices at nondominant distal radius and femoral neck; 2) subhead BMC; 3) lumbar spine BMC. Analyses accounted for baseline gynecological age (years pre- or postmenarche), baseline bone status, adult body size and interscan body size change. Gymnastics training was evaluated as a potentially independent predictor, but did not improve models for any outcomes (p < .07). Premenarcheal bone traits were strong predictors of most adult outcomes (semipartial r2 = .21-0.59, p < .001). Adult 1/3 radius and subhead BMC were predicted by both total PA and PA 1-3 years postmenarche (p < .03). PA 3-5 years postmenarche predicted femoral narrow neck width, endosteal diameter, and buckling ratio (p < .05). Thus, participation in organized physical activity programs throughout middle and high school may reduce lifetime fracture risk in females.