Abstract
Both hyponatremia and osteopenia separately have been well documented in endurance
athletes. Although bone has been shown to act as a “sodium reservoir” to buffer severe
plasma sodium derangements in animals, recent data have suggested a similar function
in humans. We aimed to explore if acute changes in bone mineral content were associated
with changes in plasma sodium concentration in runners participating in a 161 km mountain
footrace. Eighteen runners were recruited. Runners were tested immediately pre- and
post-race for the following main outcome measures: bone mineral content (BMC) and
density (BMD) via dual-energy X-ray absorptiometry (DEXA); plasma sodium concentration
([Na+]p), plasma arginine vasopressin ([AVP]p), serum aldosterone concentration ([aldosterone]s), and total sodium intake. Six subjects finished the race in a mean time of 27.0±2.3 h.
All subjects started and finished the race with [Na+]p within the normal range (137.7±2.3 and 136.7±1.6 mEq/l, pre- and post-race, respectively).
Positive correlations were noted between change (Δ; post-race minus pre-race) in total
BMC (grams) and [Na+]p (mEq/l) (r=0.99; p<0.0001), and between total sodium intake (mEq/kg) and %Δ lumbar
spine BMD (r=0.94; p<0.001). Change in [aldosterone]s was positively correlated with: rate of total sodium intake (r=0.84; p<0.05); Δ total
BMC (r=0.82; p<0.05); and Δ [Na+]p (r=0.88; p<0.05). No significant pre- to post-race mean differences were noted in
BMC or BMD. Robust associations between Δ BMC and Δ [Na+]p suggest that sodium status and bone density may be inter-related during endurance
exercise and should be considered in future investigations of athletic osteopenia.
Key words
hyponatremia - osteopenia - endurance athlete
