Mild Hyponatremia Is Not Associated With Degradation of Trabecular Bone Microarchitecture Despite Bone Mass Loss

Context: Hyponatremia is associated with increased risk of osteoporosis and fractures. The impact of hyponatremia on noninvasive indices of bone quality, however, is unknown. Objective: To evaluate whether trabecular bone microarchitecture, assessed noninvasively by trabecular bone score (TBS), is altered in patients with hyponatremia. Methods: We conducted a cross-sectional analysis of the population-based 2005-2008 cycles of the National Health and Nutrition Examination Survey, in which TBS measurement was performed. The main outcome measures were TBS values and bone mineral density (BMD) T-scores at the lumbar spine, total hip and femoral neck. Results: A total of 4204 subjects aged 50 years or older were included (4041 normonatremic, 163 hyponatremic - 90.8% with mild hyponatremia). Univariate analyses did not show any difference in TBS between patients with and without hyponatremia (1.308 ± 0.145 vs 1.311 ± 0.141, P =. 806). Hyponatremic subjects had lower BMD T-score at total hip (-0.70 ± 1.46 vs -0.13 ± 1.32, P <. 001) and femoral neck (-1.11 ± 1.26 vs -0.72 ± 1.14, P =. 004), while no difference was observed at lumbar spine (-0.27 ± 1.63 vs -0.31 ± 1.51, P =. 772). After adjustment for relevant confounders, hyponatremia was confirmed as an independent predictor of lower BMD T-score at the total hip (β = -0.20, 95% confidence interval [CI]: [-0.39, -0.02], P =. 029), while the significance was lost at the femoral neck (P =. 308). Again, no association between hyponatremia and lumbar spine BMD (P =. 236) or TBS (P =. 346) was observed. Conclusion: Hyponatremia, at least in mild forms, is not associated with a degradation of trabecular microarchitecture, assessed noninvasively by TBS. An independent association between hyponatremia and loss of bone mass is confirmed, particularly at the total hip.