Serum Sodium, Potassium, Magnesium, Calcium, and Phosphorus Levels and Risk of Fracture in the Community.

Context: Electrolytes are essential for mineral and bone metabolism. However, their associations with fracture risk among older adults have not been extensively studied.

Objective: To examine the associations of serum sodium, potassium, magnesium, calcium, and phosphorus levels with the risk of fracture.

Design: Prospective cohort study.

Setting: US community.

Participants: 5,499 older adults from the Atherosclerosis Risk in Communities Study who completed visit 5 in 2011-2013. The analysis was replicated in 11,708 middle-aged adults who completed visit 2 in 1990-1992.

Exposure: Serum levels of sodium, potassium, magnesium, calcium, and phosphorus.

Main Outcome Measure: Hospitalization with fracture ascertained through diagnostic codes on hospital discharge records.

Results: In the visit 5 cohort (mean age, 75.4 years), multivariable Cox models with restricted cubic spline terms showed significant associations of lower sodium, magnesium, and calcium levels, and higher phosphorus levels with an increased risk of fracture. In clinical categories, this association remained significant for hyponatremia (≤135 vs 135-145mEq/L) but not for hyperphosphatemia (≥4.5 vs 2.5-4.5 mg/dL) (HRs, 1.85 [95%CI, 1.22-2.81] and 2.18 [95%CI, 0.99-4.78], respectively). In the visit 2 cohort (mean age, 56.9 years), a significant association was observed for higher phosphorus levels, but not for other electrolytes, although findings were overall consistent.

Conclusions: In this community-based cohort, lower sodium, magnesium, and calcium levels, as well as higher phosphorus levels, were associated with greater fracture risk. These findings support the etiological link of serum electrolyte levels with the risk of fracture.