The effect of chronic mild hyponatremia on bone mineral loss evaluated by retrospective national Danish patient data

PURPOSE: To evaluate the effect of chronic mild hyponatremia ([Na+]=130-137mmol/L) on bone mineral content (BMC) and bone mineral density (BMD) loss through multiple, serial dual-energy X-ray absorptiometry (DXA) scans.

METHODS: Utilizing biochemical and DXA scan data from two Danish regions between 2004 and 2011, supplemented with national Danish patient diagnosis and prescription reimbursement databases, a retrospective cohort study was performed. All subjects with more than one DXA scan were included, then stratified into "normonatremia" ([Na(+)]=[137.00-147.00] mmol/L) and "mild hyponatremia" ([Na(+)]=[130.00-137.00[mmol/L) based on mean and confidence interval (CI) values calculated from all plasma sodium measurements between each subject's first and last DXA scan. Baseline, follow-up and delta values for hip and lumbar spine BMC and BMD were estimated between groups, then adjusted for comorbidity and medication use.

RESULTS: Hip and lumbar spine groups had 884 and 1069 patients with "normonatremia" versus 58 and 58 patients with "mild hyponatremia", respectively. Mild hyponatremia was associated with lower BMC and BMD in nearly all regions of the hip, and with worse losses in the trochanteric, femoral neck and total hip regions. Mild hyponatremia had limited effect on the lumbar spine.

CONCLUSIONS: Chronic mild hyponatremia seems to greatly affect bone in the hip, while the effect is limited in the lumbar spine. We suggest further retrospective study of patients with moderate (P-Na=120-130mmol/L) to severe hyponatremia (P-Na<120mmol/L) and prospective studies to further examine the association.