Bone: an acute buffer of plasma sodium during exhaustive exercise?

Area of Science:

• Exercise Physiology
• Bone Metabolism
• Endocrinology

Background:

• Hyponatremia and osteopenia are common in endurance athletes.
• Bone may function as a sodium reservoir during plasma sodium fluctuations.

Purpose of the Study:

• To investigate the relationship between acute changes in bone mineral content and plasma sodium concentration in endurance runners.
• To explore the role of bone in sodium homeostasis during prolonged exercise.

Main Methods:

• 18 runners in a 161 km mountain race were assessed pre- and post-race.
• Measurements included bone mineral content (BMC), bone mineral density (BMD) via DEXA, plasma sodium ([Na+]p), plasma arginine vasopressin ([AVP]p), and serum aldosterone ([aldosterone]s).
• Total sodium intake was also recorded.

Main Results:

• A strong positive correlation was found between changes in total BMC and plasma sodium concentration (r=0.99, p<0.0001).
• Total sodium intake correlated positively with % change in lumbar spine BMD (r=0.94, p<0.001).
• Changes in aldosterone correlated with sodium intake, BMC changes, and plasma sodium changes.

Conclusions:

• Acute changes in bone mineral content are strongly associated with plasma sodium concentration in endurance runners.
• These findings suggest an inter-relationship between sodium status and bone density during endurance exercise.
• Further research is warranted to understand the implications for athletic osteopenia.